Request | Summary | Date | Status |
---|---|---|---|
DR 1 | P1: Typos | 10/2018 | C2x |
DR 2 | P1: Functions that round result to narrower type don't always | 10/2018 | C2x |
DR 3 | P1: feature macros and header file inclusions | 10/2018 | C2x |
DR 4 | P3: Error in function name | 10/2018 | C2x |
DR 5 | P1: Is return of same type convertFormat or copy? | 10/2018 | C2x |
DR 6 | P1: fetestexceptflag and exceptions passed to fegetexceptflag | 10/2018 | C2x |
DR 7 | P1: Editorial changes | 10/2018 | C2x |
DR 8 | P2: Editorial clarification about number digits in the coefficient | 10/2018 | C2x |
DR 9 | P2,P3: Missing specification for usual arithmetic conversions, tgmath | 10/2018 | C2x |
DR 10 | P1: wrong type for fesetmode parameter | 10/2018 | C2x |
DR 11 | P2: a-style formatting not IEC 60559 conformant | 10/2018 | C2x |
DR 12 | P1: Zero payloads and set payload function | 10/2018 | C2x |
DR 13 | P3: Type-generic macros for functions that round result to narrower type | 10/2018 | Review |
DR 14 | P2: Effect of %a vs %A conversion specifiers | 10/2018 | C2x |
DR 15 | P3: Characteristic macros for non-arithmetic formats | 10/2018 | C2x |
DR 16 | P1: tgmath cbrt macro | 10/2018 | Review |
DR 17 | P3: incommensurate arguments for comparison macros | 10/2018 | C2x |
DR 18 | P4: missing specification of preferred quantum exponents | 10/2018 | Closed |
DR 19 | P1: updating underflow definition | 10/2018 | C2x |
DR 20 | P1: changes for obsolescing DECIMAL_DIG | 10/2018 | Review |
DR 21 | P1: printf of one-digit character string | 10/2018 | Review |
DR 22 | P3: changes for obsolescing DECIMAL_DIG | 10/2018 | Review |
DR 23 | P2: llquantexp invalid case | 10/2018 | Review |
DR 24 | P1 remainder NaN case | 10/2018 | Review |
DR 25 | P1 totalorder parameters | 10/2018 | Review |
DR 19 Prev <— C2x —> Next DR 2, or summary at top
Submitter: Jim Thomas et al.
Submission Date: 2016-03-19
Source: WG14
Reference Document: N2029
Subject: Part 1: Typos
Summary
Suggested Technical Corrigendum
Apr 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumProposed Technical Corrigendum
DR 19 Prev <— C2x —> Next DR 2, or summary at top
DR 1 Prev <— C2x —> Next DR 3, or summary at top
Submitter: Jim Thomas et al.
Submission Date: 2016-03-19
Source: WG14
Reference Document: N2029
Subject: Part 1: Functions that round result to narrower type don't always
Summary
Summary
Page 38: The C 7.12.13a subclause heading is “Functions that round result to narrower type” and this is the way the functions in the subclause are referred to throughout the TS. In some cases, the functions in the subclause round their result to a type that isn’t really narrower than the parameter types. For example, this is true for the functions daddl, dsubl, etc. if the long double and double types have the same width (as is allowed). (With the extended types introduced in TS 18661-3, the destination type might be wider, as it might for f32xaddf64.)The current way of referencing these functions reflects the usual situation, and is perhaps a helpful way of think about them generally. With a note about the uncharacteristic cases, it seems unlike to cause significant confusion. Also, changing all the references to these functions would be a large editorial undertaking, spanning multiple parts of the TS. Confusion could easily arise from having an inconsistent set of documents.
Suggested Technical Corrigendum
Page 38: After the C 7.12.13a subclause heading, insert the following paragraph:[1] The functions in this subclause round their results to a type typically narrower than the parameter types.
In 7.12.13a #1, attach a footnote to the wording:typically narrowerwhere the footnote is:*) In some cases the destination type might not be narrower than the parameter types. For example, double might not be narrower than long double.
Apr 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumProposed Technical Corrigendum
Page 38: After the C 7.12.13a subclause heading, insert the following paragraph:
[1] The functions in this subclause round their results to a type typically narrower than the parameter types.
In 7.12.13a #1, attach a footnote to the wording:typically narrowerwhere the footnote is:*) In some cases the destination type might not be narrower than the parameter types. For example, double might not be narrower than long double.
DR 1 Prev <— C2x —> Next DR 3, or summary at top
DR 2 Prev <— C2x —> Next DR 4, or summary at top
Submitter: Jim Thomas et al.
Submission Date: 2016-03-19
Source: WG14
Reference Document: N2029
Subject: Part 1: feature macros and header file inclusions/p>
Summary
ISO/IEC TS 18661-1 subclause 5.3 specifies interfaces that are defined or declared “only if __STDC_WANT_IEC_60559_BFP_EXT__ is defined as a macro at the point in the source file where the header for the interface is first included.” C 7.12#1 says <tgmath.h> includes <math.h> and <complex.h>.So for
#include <math.h>
#define __STDC_WANT_IEC_60559_BFP_EXT__
#include <tgmath.h>
float f(float x) { return nextup(x); }
the nextup functions in <math.h> are not declared and the nextup macro in <tgmath.h> is defined. Since x has type float, the function determined by the nextup macro in <tgmath.h> is nextupf. But is this function available to be called?
Another example. For
#include <limits.h>
#define __STDC_WANT_IEC_60559_BFP_EXT__
#include <math.h>
...
the fromfp functions in <math.h> are declared, but the WIDTH macros in <limits.h>, which are needed for portable use of the fromfp functions, are not defined.
In these examples, interfaces provided by one header are related to interfaces that are not provided by another header, because of the placement of the WANT macros. This leads to ambiguous cases (as in the first example above) and incomplete feature sets. Later parts of the TS have their own WANT macros, which compounds the problem. See also Joseph Myers’s The suggested corrigendum below specifies that the same set of WANT macros must be defined at the points in the code where the relevant headers are first included. This results in fewer combinations of interfaces and provides one sets of interfaces that is consistent and complete with respect to a given set of WANT macros.
Suggested Technical Corrigendum
Page 5: At the end of 5.3, insert:After 7.1.2#4, insert:[4a] Some standard headers define or declare identifiers contingent on whether certain macros whose names begin with _STDC_WANT_IEC_60559_ and end with _EXT_ are defined (by the user) at the point in the code where the header is first included. Within a preprocessing translation unit, the same set of such macros shall be defined for the first inclusion of all such headers.
Apr 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumProposed Technical Corrigendum
Page 5: At the end of 5.3, insert:
After 7.1.2#4, insert:[4a] Some standard headers define or declare identifiers contingent on whether certain macros whose names begin with _STDC_WANT_IEC_60559_ and end with _EXT_ are defined (by the user) at the point in the code where the header is first included. Within a preprocessing translation unit, the same set of such macros shall be defined for the first inclusion of all such headers.
DR 2 Prev <— C2x —> Next DR 4, or summary at top
DR 3 Prev <— C2x —> Next DR 5, or summary at top
Submitter: Jim Thomas et al.
Submission Date: 2016-03-19
Source: WG14
Reference Document: N2029
Subject: Part 3: Error in function name/p>
Summary
Page 32: In 12.3, the function name is written as “scoshdNx”, instead of “coshdNx” as intended. Although correcting the mistake could be seen as a substantive change, it is clear from the context that this function is in the family of cosh functions. It is extremely unlikely that any implementer would not have recognized the mistake and provided the function with the erroneous name.Suggested Technical Corrigendum
Page 32: In 12.3, change “scoshdNx” to “coshdNx”.Apr 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumProposed Technical Corrigendum
Page 32: In 12.3, change “scoshdNx” to “coshdNx”.
DR 3 Prev <— C2x —> Next DR 5, or summary at top
DR 4 Prev <— C2x —> Next DR 6, or summary at top
Submitter: Jim Thomas
Submission Date: 2016-09-10
Source: WG14
Reference Document: N2077
Subject: Part 1: Is return of same type convertFormat or copy?
Summary
Summary
This is about
the issue raised by Joseph Myers in email SC22WG14.14280:
TS 18661-1 says "Whether C assignment (6.5.16) (and conversion as if
by assignment) to the same format is an IEC 60559 convertFormat
or copy operation is implementation-defined, even if <fenv.h> defines the
macro
FE_SNANS_ALWAYS_SIGNAL (F.2.1).".
Does this
apply to function return, where the return type of the function is the same as
the type of the expression passed to the return statement and no wider
evaluation format is in use - that is, may this act as either convertFormat or copy? C11 F.6 clearly envisages that
such a return statement may do a conversion to the same type in the case of
wider evaluation formats. But 6.8.6.4#3 only refers to conversions
"If the expression has a type different from the return type of the
function in which it appears".
The specification, from F.3#3, quoted
above is incomplete in that it doesn’t cover function returns, which are not
assignments or conversions as if by assignment. As currently written, C11 +
TS18661-1 might be read to exclude the possibility of using convertFormat
in this case. A statement should be added to say that the implementation has
the option to apply convertFormat to the return value.
The change does not break existing implementations.
The effect of convertFormat
would be that signaling NaNs would signal and noncanonical representations would be canonicalized.
It is extremely unlikely that a program would depend on convertFormat
not being used.
Suggested
Technical Corrigendum
In Clause 8, to the text for C F.3#3:
[3] Whether C
assignment (6.5.16) (and conversion as if by assignment) to the same format is
an IEC 60559 convertFormat or copy operation is
implementation-defined, even if <fenv.h> defines the macro FE_SNANS_ALWAYS_SIGNAL (F.2.1).
append the sentence:
If the return
expression of a return statement is evaluated to the
floating-point format of the return type, it is implementation-defined whether
a convertFormat operation is applied to the result of
the return expression.”
At the end of Clause 8, add:
In F.3#3,
attach a footnote to the wording:
Whether C
assignment (6.5.16) (and conversion as if by assignment) to the same format is
an IEC 60559 convertFormat or copy operation
where the
footnote is:
*) Where the
source and destination formats are the same, convertFormat
operations differ from copy operations in that convertFormat
operations raise the “invalid” floating-point exception on signaling NaN inputs and do not propagate non-canonical encodings.
Oct 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumProposed Technical Corrigendum
In Clause 8, to the text for C F.3#3:
[3] Whether C
assignment (6.5.16) (and conversion as if by assignment) to the same format is
an IEC 60559 convertFormat or copy operation is
implementation-defined, even if <fenv.h> defines the macro FE_SNANS_ALWAYS_SIGNAL (F.2.1).
append the sentence:
If the return
expression of a return statement is evaluated to the
floating-point format of the return type, it is implementation-defined whether
a convertFormat operation is applied to the result of
the return expression.”
At the end of Clause 8, add:
In F.3#3,
attach a footnote to the wording:
Whether C
assignment (6.5.16) (and conversion as if by assignment) to the same format is
an IEC 60559 convertFormat or copy operation
where the
footnote is:
*) Where the
source and destination formats are the same, convertFormat
operations differ from copy operations in that convertFormat
operations raise the “invalid” floating-point exception on signaling NaN inputs and do not propagate non-canonical encodings.
DR 4 Prev <— C2x —> Next DR 6, or summary at top
DR 5 Prev <— C2x —> Next DR 7, or summary at top
Submitter: Jim Thomas
Submission Date: 2016-09-10
Source: WG14
Reference Document: N2077
Subject: Part 1: fetestexceptflag and exceptions passed to fegetexceptflag
Summary
This is about the issue raised by Joseph
Myers in email SC22WG14.14328:
TS 18661-1
says, for fetestexceptflag, "The value of *flagp shall have been set by a previous call to fegetexceptflag.".
This
contrasts with the C11 wording for fesetexceptflag, "The value of *flagp shall have been set by a previous call to fegetexceptflag whose second argument represented at least those floating-point
exceptions represented by the argument excepts.". So what happens if more exceptions are specified in the
call to fetestexceptflag than were specified in the call to fegetexceptflag? Then fegetexceptflag may or may not have stored any meaningful representation of the state of
the extra exceptions being tested.
I think fetestexceptflag should have
the same wording for this issue as fesetexceptflag: "whose second argument represented at least those floating-point
exceptions represented by the argument excepts".
fesetexceptflag sets global state, typically a hardware register, whereas fetestexceptflag just reads a
variable. It seems more important to avoid spurious data in the former.
Still, there’s no utility in testing
spurious flag settings, and placing the same restrictions on fetestexceptflag as on fesetexceptflag might be
less error prone.
Suggested
Technical Corrigendum
In 15.2, in the new text for C 7.6.2.4a#2,
change:
The value of *flagp shall have
been set by a previous call to fegetexceptflag.
to:
The value of *flagp shall have been set by a previous
call to fegetexceptflag whose second argument represented at least those floating-point
exceptions represented by the argument excepts.
Oct 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumProposed Technical Corrigendum
In 15.2, in the new text for C 7.6.2.4a#2,
change:
The value of *flagp shall have
been set by a previous call to fegetexceptflag.
to:
The value of *flagp shall have been set by a previous
call to fegetexceptflag whose second argument represented at least those floating-point
exceptions represented by the argument excepts.
DR 5 Prev <— C2x —> Next DR 7, or summary at top
DR 6 Prev <— C2x —> Next DR 8, or summary at top
Submitter: Jim Thomas
Submission Date: 2016-09-10
Source: WG14
Reference Document: N2077
Subject: Part 1: Editorial changes
Summary
Summary
In CFP email, Fred Tydeman
noted:
Searching for
"infinite precision" in part 1, most of them have "(as if)
to" before it. Except, ffma, ffmal, dfmal which is missing the "(as
if)".
Right. In particular, all the functions
that round result to narrower type have “(as if)”, except for the fma family.
Suggested
Technical Corrigendum
In 14.5, in the new text for C
7.12.13a.5#2, insert “(as if)” before “to infinite precision”.
Oct 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumProposed Technical Corrigendum
In 14.5, in the new text for C
7.12.13a.5#2, insert “(as if)” before “to infinite precision”.
DR 6 Prev <— C2x —> Next DR 8, or summary at top
DR 7 Prev <— C2x —> Next DR 9, or summary at top
Submitter: Jim Thomas
Submission Date: 2016-09-10
Source: WG14
Reference Document: N2077
Subject: Part 2: Editorial clarification about number digits in the coefficient
Summary
Summary
In
12.5, n is defined to be “the number of digits in the coefficient c”, where the decimal floating-point
argument is represented by the triple (s,
c, q). The intention is that n
is the number of digits in the coefficient of the particular argument, i.e.,
the number of significant digits, not the maximum number of digits in the
coefficient for the type. This might be misread, particularly since 5.2.4.2.2a says
¾
number of digits in the coefficient
DEC32_MANT_DIG 7
DEC64_MANT_DIG 16
DEC128_MANT_DIG 34
This part of 5.2.4.2.2a is in the context of
characterizing the type, so clearly refers to the type and not any particular
representation.
Suggested
Technical Corrigendum
In 12.5, change:
where n is the number of digits in the
coefficient c
to:
where
n is the number of significant digits
in the coefficient c
Oct 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumProposed Technical Corrigendum
In 12.5, change:
where n is the number of digits in the
coefficient c
to:
where
n is the number of significant digits
in the coefficient c
DR 7 Prev <— C2x —> Next DR 9, or summary at top
DR 8 Prev <— C2x —> Next DR 10, or summary at top
Submitter: Jim Thomas
Submission Date: 2016-09-10
Source: WG14
Reference Document: N2077
Subject: Part 2,3: Missing specification for usual arithmetic conversions, tgmath
Summary
This is about
the issue raised by Joseph Myers in email SC22WG14.14282:
C11 specifies that the usual arithmetic conversions on the pair of types
(long
double, double)
produces a result of type long double.
Suppose long double and double have the same set of values.
TS 18661-3 rewrites the rules for usual arithmetic conversions so that
the case "if both operands are floating types and the sets of values of
their corresponding real types are equivalent" prefers interchange types
to standard types to extended types. But this leaves the case of (long double, double) unspecified as to which type is
chosen, unlike in C11, as those are both standard types.
I think this
is a defect in TS 18661-3, and it should say that if both are standard types
with the same set of values then long double is preferred to double which is
preferred to float, as in C11.
A similar
issue could arise if two of the extended types have equivalent sets of values.
I'm not aware of anything to prohibit that, although it seems less likely
in practice. I think the natural fix would be to say that _Float128x is preferred to _Float64x which is
preferred to _Float32x.
I think such
an issue would also arise for <tgmath.h> (if _Float64x and _Float128x have the same set of values, the choice doesn't seem to be specified).
It also seems possible for the <tgmath.h> rules for purely floating-point arguments to produce a different result
from the usual arithmetic conversions (consider the case where _Float32x is wider than long double, and <tgmath.h> chooses long double), and since rules that are the same in most cases but subtly different
in obscure cases tend to be confusing, I wonder if it might be better to
specify much simpler rules for <tgmath.h>: take the type resulting from the usual arithmetic conversions[*], where
integer arguments are replaced by _Decimal64 if there are any decimal arguments and double otherwise. (That's different from the present rules for e.g. (_Float32x, int), but it's a
lot simpler, and seems unlikely in practice to choose a type with a different
set of values from the present choice.)
[*]
Meaningful for more than two arguments as long as the usual arithmetic
conversions are commutative and associative as an operation on pairs of types.
Though substantive, the suggested change
to the usual arithmetic conversions is consistent with the intention in TS
18661-3 to specify all the cases (except where neither format is a subset of
the other and the formats are not the same). The missing cases were an
oversight. The suggested preferences of long double over double over float and _Float128x over _Float64x over _Float32x are the obvious choices.
Joseph Myers notes that the <tgmath.h>
specification is incomplete in the same way as the usual arithmetic conversions.
He argues for simplifying the specification by referring to the usual
arithmetic conversions specification, rather than mostly repeating it, as the
current specification does. The suggested Technical Corrigendum below follows
this new approach. Though a substantive change to TS 18661-3, the effects on
implementations and users are expected to be minimal – worth the
simplification.
The suggested Technical Corrigendum
below also restores footnote number 62, which is lost in the current TS
18661-3.
Suggested
Technical Corrigendum
In clause 8, change the replacement text
for 6.3.1.8#1:
If one
operand has decimal floating type, the other operand shall not have standard
floating type, binary floating type, complex type, or imaginary type.
If both
operands have floating types and neither of the sets of values of their
corresponding real types is a subset of (or equivalent to) the other, the
behavior is undefined.
Otherwise, if
both operands are floating types and the sets of values of their corresponding
real types are equivalent, then the following rules are applied:
If both
operands have the same corresponding real type, no further conversion is
needed.
Otherwise, if
the corresponding real type of either operand is an interchange floating type,
the other operand is converted, without change of type domain, to a type
whose corresponding real type is that same interchange floating type.
Otherwise, if
the corresponding real type of either operand is a standard floating type, the
other operand is converted, without change of type domain, to a type
whose corresponding real type is that same standard floating type.
Otherwise, if
both operands have floating types, the operand, whose set of values of its
corresponding real type is a (proper) subset of the set of values of the
corresponding real type of the other operand, is converted, without change of
type domain, to a type with the corresponding real type of that other operand.
Otherwise, if
one operand has a floating type, the other operand is converted to the
corresponding real type of the operand of floating type.
Otherwise,
the integer promotions are performed on both operands. Then the following rules
are applied to the promoted operands:
. . .
to:
If one
operand has decimal floating type, the other operand shall not have standard
floating type, binary floating type, complex type, or imaginary type.
If both
operands have floating types and neither of the sets of values of their
corresponding real types is a subset of (or equivalent to) the other, the
behavior is undefined.
If both
operands have the same corresponding real type, no further conversion is
needed.
Otherwise, if
both operands are floating types and the sets of values of their corresponding
real types are equivalent, then the following rules are applied:
If the
corresponding real type of either operand is an interchange floating type, the
other operand is converted, without change of type domain, to a type
whose corresponding real type is that same interchange floating type.
Otherwise, if
the corresponding real type of either operand is long double, the other operand is converted, without change of
type domain, to a type whose corresponding real type is long double.
Otherwise, if
the corresponding real type of either operand is double, the other operand is converted, without change of
type domain, to a type whose corresponding real type is double.
(All cases
where float might have the same format as
another type are covered above.)
Otherwise, if
the corresponding real type of either operand is _Float128x or _Decimal128x, the other operand is
converted, without change of type domain, to a type whose corresponding
real type is _Float128x or _Decimal128x, respectively.
Otherwise, if
the corresponding real type of either operand is _Float64x or _Decimal64x, the other operand is
converted, without change of type domain, to a type whose corresponding
real type is _Float64x or _Decimal64x, respectively.
Otherwise, if
both operands have floating types, the operand, whose set of values of its
corresponding real type is a (proper) subset of the set of values of the
corresponding real type of the other operand, is converted, without change of
type domain62), to a type with the corresponding real type of that other
operand.
Otherwise, if
one operand has a floating type, the other operand is converted to the
corresponding real type of the operand of floating type.
Otherwise,
the integer promotions are performed on both operands. Then the following rules
are applied to the promoted operands:
. . .
In clause 15, replace:
In 7.25#3c, replace the bullets:
… bullets …
with:
— If two arguments have floating types and neither of the
sets of values of their corresponding real types is a subset of (or equivalent
to) the other, the behavior is undefined.
— If any arguments for generic parameters have type _DecimalM where M
≥ 64 or _DecimalNx where N ≥ 32, the type determined is the widest of the types of these
arguments. If _DecimalM and _DecimalNx are both widest types (with equivalent sets
of values) of these arguments, the type determined is _DecimalM.
— Otherwise, if any argument for generic parameters is of
integer type and another argument for generic parameters has type _Decimal32, the type determined is _Decimal64.
— Otherwise, if any argument for generic parameters has type _Decimal32, the type determined is _Decimal32.
— Otherwise, if the corresponding real type of any argument
for generic parameters has type long double, _FloatM where M
≥ 128, or _FloatNx where N ≥ 64, the type determined is the widest of the corresponding real
types of these arguments. If _FloatM and either long double or _FloatNx are both widest corresponding real types (with equivalent sets of
values) of these arguments, the type determined is _FloatM. Otherwise, if long double and _FloatNx are both widest corresponding real types
(with equivalent sets of values) of these arguments, the type determined is long double.
— Otherwise, if the corresponding real type of any argument
for generic parameters has type double, _Float64, or _Float32x, the type determined is the
widest of the corresponding real types of these arguments. If _Float64 and either double or _Float32x are both widest
corresponding real types (with equivalent sets of values) of these arguments,
the type determined is _Float64. Otherwise, if double and _Float32x are both widest
corresponding real types (with equivalent sets of values) of these arguments,
the type determined is double.
— Otherwise, if any argument for generic parameters is of
integer type, the type determined is double.
— Otherwise, if the corresponding real type of any argument
for generic parameters has type _Float32, the type determined is _Float32.
— Otherwise, the type determined is float.
In the
second bullet 7.25#3c, attach a footnote to the wording:
the type
determined is the widest
where the
footnote is:
*) The
term widest here refers to a type whose set of values is a superset of (or
equivalent to) the sets of values of the other types.
with:
In 7.25#3c, replace the first sentence and bullets:
[3c] Except for the macros for functions that round result to a narrower type
(7.12.13a), use of a
type-generic macro invokes a function whose generic parameters have the
corresponding real type determined by the corresponding real types of the
arguments as follows:
— First, if
any argument for generic parameters has type _Decimal128, the type determined is _Decimal128.
— Otherwise,
if any argument for generic parameters has type _Decimal64, or if any argument for generic parameters is of integer type and
another argument for generic parameters has type _Decimal32, the type determined is _Decimal64.
— Otherwise,
if any argument for generic parameters has type _Decimal32, the type determined is _Decimal32.
— Otherwise,
if the corresponding real type of any argument for generic parameters is long double, the type determined is long double.
— Otherwise,
if the corresponding real type of any argument for generic parameters is double or is of integer type, the type determined is double.
— Otherwise,
if any argument for generic parameters is of integer type, the type determined
is double.
— Otherwise,
the type determined is float.
with:
[3c] Except
for the macros for functions that round result to a narrower type (7.12.13a), use of a type-generic macro invokes a function
whose generic parameters have the corresponding real
type determined by the types of the arguments for the generic
parameters as follows:
— Arguments
of integer type are regarded as having type _Decimal64 if any argument has decimal floating type,
and as having type double otherwise.
— If
the function has exactly one generic parameter, the type determined is
the corresponding real type of the argument for the generic
parameter.
— If
the function has exactly two generic parameters, the type determined is
the corresponding real type determined by the usual arithmetic
conversions (6.3.1.8) applied to the arguments for the
generic parameters.
— If
the function has more than two generic parameters, the type determined is
the corresponding real type determined by repeatedly applying the usual
arithmetic conversions, first to the first two arguments for generic
parameters, then to that result type and the next argument for a generic
parameter, and so forth until the usual arithmetic conversions have been
applied to the last argument for a generic parameter.
Oct 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumApr 2017 meeting
Committee Discussion
A new paper N2127 was presented which offers a simplified Technical Corrigendum. From that paper:The committee accepts the proposed modification as reflected below.The TC in DR 501 includes two changes to TS 18661-3, one for the usual arithmetic conversions, the other for type-generic math. The first change fills in missing conversions for new types in TS 18661-3. The second change simplifies type-generic math by referencing the usual arithmetic conversions, and thereby also fills in missing type-generic math rules for arguments of the new types.
This is a proposal for an alternative change to type-generic math. The original change was proposed for TS 18661-3, where the new types where introduced. However, the change can be made in TS 18661-2, where it is easier to understand and leads to a simplification in TS 18661-3.
Proposed Technical Corrigendum
In TS 18662-3
In clause 8, change the replacement text
for 6.3.1.8#1:
If one
operand has decimal floating type, the other operand shall not have standard
floating type, binary floating type, complex type, or imaginary type.
If both
operands have floating types and neither of the sets of values of their
corresponding real types is a subset of (or equivalent to) the other, the
behavior is undefined.
Otherwise, if
both operands are floating types and the sets of values of their corresponding
real types are equivalent, then the following rules are applied:
If both
operands have the same corresponding real type, no further conversion is
needed.
Otherwise, if
the corresponding real type of either operand is an interchange floating type,
the other operand is converted, without change of type domain, to a type
whose corresponding real type is that same interchange floating type.
Otherwise, if
the corresponding real type of either operand is a standard floating type, the
other operand is converted, without change of type domain, to a type
whose corresponding real type is that same standard floating type.
Otherwise, if
both operands have floating types, the operand, whose set of values of its
corresponding real type is a (proper) subset of the set of values of the
corresponding real type of the other operand, is converted, without change of
type domain, to a type with the corresponding real type of that other operand.
Otherwise, if
one operand has a floating type, the other operand is converted to the
corresponding real type of the operand of floating type.
Otherwise,
the integer promotions are performed on both operands. Then the following rules
are applied to the promoted operands:
. . .
to:
If one
operand has decimal floating type, the other operand shall not have standard
floating type, binary floating type, complex type, or imaginary type.
If both
operands have floating types and neither of the sets of values of their
corresponding real types is a subset of (or equivalent to) the other, the
behavior is undefined.
If both
operands have the same corresponding real type, no further conversion is
needed.
Otherwise, if
both operands are floating types and the sets of values of their corresponding
real types are equivalent, then the following rules are applied:
If the
corresponding real type of either operand is an interchange floating type, the
other operand is converted, without change of type domain, to a type
whose corresponding real type is that same interchange floating type.
Otherwise, if
the corresponding real type of either operand is long double, the other operand is converted, without change of
type domain, to a type whose corresponding real type is long double.
Otherwise, if
the corresponding real type of either operand is double, the other operand is converted, without change of
type domain, to a type whose corresponding real type is double.
(All cases
where float might have the same format as
another type are covered above.)
Otherwise, if
the corresponding real type of either operand is _Float128x or _Decimal128x, the other operand is
converted, without change of type domain, to a type whose corresponding
real type is _Float128x or _Decimal128x, respectively.
Otherwise, if
the corresponding real type of either operand is _Float64x or _Decimal64x, the other operand is
converted, without change of type domain, to a type whose corresponding
real type is _Float64x or _Decimal64x, respectively.
Otherwise, if
both operands have floating types, the operand, whose set of values of its
corresponding real type is a (proper) subset of the set of values of the
corresponding real type of the other operand, is converted, without change of
type domain62), to a type with the corresponding real type of that other
operand.
Otherwise, if
one operand has a floating type, the other operand is converted to the
corresponding real type of the operand of floating type.
Otherwise,
the integer promotions are performed on both operands. Then the following rules
are applied to the promoted operands:
. . .
In TS 18661-2
In 12.9, change the introduced [3c] from:
[3c] Except for the macros for functions that round result to a narrower type
(7.12.13a), use of a
type-generic macro invokes a function whose generic parameters have the
corresponding real type determined by the corresponding real types of the
arguments as follows:
— First, if any argument for
generic parameters has type _Decimal128, the type determined is _Decimal128.
— Otherwise, if any argument for
generic parameters has type _Decimal64, or if any argument for generic
parameters is of integer type and another argument for generic parameters has
type _Decimal32, the type determined is _Decimal64.
— Otherwise, if any argument for
generic parameters has type _Decimal32, the type determined is _Decimal32.
— Otherwise, if the corresponding
real type of any argument for generic parameters is long double, the type determined is long double.
— Otherwise, if the corresponding
real type of any argument for generic parameters is double or is of integer type, the type determined
is double.
— Otherwise, if any argument for
generic parameters is of integer type, the type determined is double.
— Otherwise, the type determined is
float.
to:
[3c] Except for the macros for functions
that round result to a narrower type (7.12.13a), use of a
type-generic macro invokes a function whose generic parameters have
the corresponding real type determined by the types of the arguments for
the generic parameters as follows:
— Arguments of
integer type are regarded as having type _Decimal64 if any
argument has decimal floating type, and as having type double otherwise.
— If the
function has exactly one generic parameter, the type determined
is the corresponding real type of the argument for
the generic parameter.
— If the
function has exactly two generic parameters, the type determined
is the corresponding real type determined by the
usual arithmetic conversions (6.3.1.8) applied to the arguments for
the generic parameters.
— If the
function has more than two generic parameters, the type determined
is the corresponding real type determined by repeatedly applying
the usual arithmetic conversions, first to the first two arguments
for generic parameters, then to that result type and the next
argument for a generic parameter, and so forth until the usual arithmetic
conversions have been applied to the last argument for a generic
parameter.
DR 8 Prev <— C2x —> Next DR 10, or summary at top
DR 9 Prev <— C2x —> Next DR 11, or summary at top
Submitter: Jim Thomas
Submission Date: 2016-09-10
Source: WG14
Reference Document: N2077
Subject: Part 1: wrong type for fesetmode parameter
Summary
This is about the issue raised by Joseph
Myers in email SC22WG14.14358:
TS 18661-1
gives the declaration of fesetmode as:
int fesetmode(const fenv_t *modep);
The argument
should be of type const femode_t *, not const fenv_t *.
--
This was an editorial cut-and-past
error. The Description says the argument modep shall point to an objet set by a call to fegetmode, which sets objects of type femode_t. It’s unlikely the function would be implemented with the erroneous
type.
Suggested
Technical Corrigendum
In 15.3, in the new text for C
7.6.3.1a#1, change:
int fesetmode(const
fenv_t *modep);
to:
int fesetmode(const
femode_t *modep);
Oct 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumProposed Technical Corrigendum
In 15.3, in the new text for C
7.6.3.1a#1, change:
int fesetmode(const
fenv_t *modep);
to:
int fesetmode(const
femode_t *modep);
DR 9 Prev <— C2x —> Next DR 11, or summary at top
DR 10 Prev <— C2x —> Next DR 12, or summary at top
Submitter: Jim Thomas
Submission Date: 2016-09-10
Source: WG14
Reference Document: N2077
Subject: Part 2: a-style formatting not IEC 60559 conformant
Summary
The a-style
formatting specified in subclause 12.5 of TS 18661-2
is not an IEC 60559 conversion for cases where the formatting precision is less
than the length of the coefficient of the input. The specification entails an
intermediate rounding to the floating type of the input, which might overflow resulting
in a character sequence representation of infinity. IEC 60559 conversions to
character sequences do not overflow, unless the language over-restricts the
exponent range for character sequence output, which C does not.
Another undesirable aspect of the
current specification is that in certain cases it produces results with more
precision than given by a width modifier.
Here are some examples, showing the
result of the intermediate conversion, with different behaviors for the current
spec (“old”) and the spec in the suggested Technical Corrigendum below (“new”):
For _Decimal32 input x with representation
(1, 9512345, 90) and specifier ...
%.3Ha
old: x -> (1,
9510000, 90) -> 9.510000e96
new: x -> (1,
951, 94) -> 9.51e96
%.2Ha
old: x -> (1,
9500000, 90) -> 9.500000e96
new: x -> (1,
95, 95) -> 9.5e96
%.1Ha
old: x -> Inf -> inf
new: x -> (1,
1, 97) -> 1e97
Here’s another example:
For _Decimal32 input x with representation (1, 9512345, 86) and specifier
...
%.2Ha
old: x -> (1,
950, 90) -> 9.50e92
new: x -> (1,
95, 91) -> 9.5e92
The examples use a to-nearest rounding.
As the examples illustrate, the problematic
cases for the current “old” spec occur because of the exponent range limitation
of the format used for the intermediate conversion.
The suggested Technical Corrigendum
below specifies formatting that is IEC 60559 conformant and which honors a
width modifier. It does not change the numerical value of the result, except in
overflow cases.
Suggested
Technical Corrigendum
In 12.5, in the addition to 7.21.6.1#8 and 7.29.2.1#8,
under a,A
conversion specifiers, change:
If the precision is present (in the conversion
specification) and is zero or at least as large as the precision p (5.2.4.2.2) of the decimal floating
type, the conversion is as if the precision were missing. If the precision is
present (and nonzero) and less than the precision p of the decimal floating type, the conversion first obtains an
intermediate result by rounding the input in the type, according to the current
rounding direction for decimal floating-point operations, to the number of
digits specified by the precision, then converts the intermediate result as if
the precision were missing. The length of the coefficient of the intermediate
result is the smallest number, at least as large as the formatting precision,
for which the quantum exponent is within the quantum exponent range of the type
(see 5.2.4.2.2a). The intermediate rounding may overflow.
to:
If the
precision P is present (in the
conversion specification) and is zero or at least as large as the precision p (5.2.4.2.2) of the decimal floating
type, the conversion is as if the precision were missing. If the precision
P is present (and nonzero) and less
than the precision p of the decimal
floating type, the conversion first obtains an intermediate result as follows,
where n is the number of significant
digits in the coefficient:
If n <= P, set the intermediate result to the input.
If n > P, round the input value, according to the current rounding
direction for decimal floating-point operations, to P decimal digits, with unbounded exponent range, representing the
result with a P-digit integer
coefficient when in the form (s, c, q).
Convert the
intermediate result in the manner described above for the case where the
precision is missing.
In 12.5, in the addition to 7.21.6.1#8 and 7.29.2.1#8, in
EXAMPLE 3, change the results:
9.54321e+93
9.5432e+93
9.543e+93
9.540e+93
9.500e+93
1.0000e+94
inf
to:
9.54321e+93
9.5432e+93
9.543e+93
9.54e+93
9.5e+93
1e+94
1e+97
Oct 2016 meeting
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical CorrigendumApr 2017 meeting
Committee Discussion
The paper N2126 provides an example that illustrates this change, and the committee agreed to accept this as an addendum to the Proposed Technical Corrigendum.However, the committee is concerned that %a behavior differs from binary floating point and more review is needed. In particular, there were concerns that for the decimal floating point types now the %a format specifier given with a precision is the total number of significant digits, not the number of digits after the decimal point as it has been for other data types.
Proposed Technical Corrigendum
In 12.5, in the addition to 7.21.6.1#8 and 7.29.2.1#8,
under a,A
conversion specifiers, change:
If the precision is present (in the conversion
specification) and is zero or at least as large as the precision p (5.2.4.2.2) of the decimal floating
type, the conversion is as if the precision were missing. If the precision is
present (and nonzero) and less than the precision p of the decimal floating type, the conversion first obtains an
intermediate result by rounding the input in the type, according to the current
rounding direction for decimal floating-point operations, to the number of
digits specified by the precision, then converts the intermediate result as if
the precision were missing. The length of the coefficient of the intermediate
result is the smallest number, at least as large as the formatting precision,
for which the quantum exponent is within the quantum exponent range of the type
(see 5.2.4.2.2a). The intermediate rounding may overflow.
to:
If the
precision P is present (in the
conversion specification) and is zero or at least as large as the precision p (5.2.4.2.2) of the decimal floating
type, the conversion is as if the precision were missing. If the precision
P is present (and nonzero) and less
than the precision p of the decimal
floating type, the conversion first obtains an intermediate result as follows,
where n is the number of significant
digits in the coefficient:
If n <= P, set the intermediate result to the input.
If n > P, round the input value, according to the current rounding
direction for decimal floating-point operations, to P decimal digits, with unbounded exponent range, representing the
result with a P-digit integer
coefficient when in the form (s, c, q).
Convert the
intermediate result in the manner described above for the case where the
precision is missing.
In 12.5, in the addition to 7.21.6.1#8 and 7.29.2.1#8, in
EXAMPLE 3, change the results:
9.54321e+93
9.5432e+93
9.543e+93
9.540e+93
9.500e+93
1.0000e+94
inf
to:
9.54321e+93
9.5432e+93
9.543e+93
9.54e+93
9.5e+93
1e+94
1e+97
Add, as a new EXAMPLE,
#include <stdio.h> int main(void) { _Decimal32 x = 9512345e90df; _Decimal32 x2 = 9512345e86df; printf("%.3Ha\n", x); // New expected output: 9.51e96 printf("%.2Ha\n", x); // New expected output: 9.5e96 printf("%.1Ha\n", x); // New expected output: 1e97 printf("%.2Ha\n", x2); // New expected output: 9.5e92 return 0; }
DR 10 Prev <— C2x —> Next DR 12, or summary at top
DR 11 Prev <— C2x —> Next DR 14, or summary at top
Submitter: Jim Thomas
Submission Date: 2017-03-04
Source: WG14
Reference Document: N2125
Subject: P1: Zero payloads and set payload function
Summary
This is about an issue raised
by Joseph Myers in SC22WG14.14450:
The
specification for setpayload (and likewise setpayloadsig)
says "If pl is not a positive floating-point integer representing
a valid payload, *res is set to positive zero."
Does
"positive" as applied to "floating-point integer" here mean
"with sign bit 0" (the list of definitions in IEEE 754 doesn't
include "positive")? In the preferred encodings for binary
interchange formats, 0 is a valid payload for quiet NaNs.
So should +0.0 as an argument to setpayload
result in a quiet NaN with payload 0, while -0.0
results in *res being set to +0.0 because -0.0 isn't positive (and
for setpayloadsig, both result in *res set to +0.0 because a payload for a signaling NaN has to be nonzero to avoid all mantissa bits being
zero)?
A “positive floating-point integer” is a positive
integer in the floating-point format, hence it is
greater than zero. So, the current specification for setpayload and setpayloadsig is flawed in that it doesn’t
allow setting the payload to zero.
A more basic problem is that TS 18661-1 assumes IEC
60559 interprets payloads as integers. This is true for decimal formats. IEC
60559 says:
The
payload corresponds to the significand of finite
numbers, interpreted as an integer with a maximum value of 10^(3×J)−1, …
The significand c
interpreted as an integer is assumed throughout to be non-negative, while the s field in (s, q, c) provides the sign. For decimal,
interpreting the bits in the encodings allows the two encoding schemes to have
the same payloads and the payloads to fit conceptually with their encoding
schemes.
However, for binary formats, IEC 60559 says:
For
binary formats, the payload is encoded in the p−2 least significant bits of the trailing significand field.
Nowhere does it actually interpret the payload for
binary formats as an integer.
However, the payload for binary formats has a natural
interpretation as an unsigned integer, so it is reasonable for TS 1866-1 to
interpret payloads (for binary and decimal formats) as such.
The suggested Technical Corrigendum below addresses
these problems.
Suggested Technical Corrigendum
In 14.10, replace the first
sentence:
IEC 60559 defines the payload of a NaN to be a certain part of the NaN’s
significand interpreted as an integer.
with:
IEC 60559 defines the payload of a NaN to be a certain part of the NaN’s
significand. The payload can be interpreted as an
unsigned integer.
In 14.10, in the new C subclause F.10.13, replace:
IEC 60559 defines the payload of a quiet or signaling NaN as an integer value encoded in the significand.
with:
IEC 60559 defines the payload of a quiet or signaling NaN as information encoded in part of the NaN significand. The payload can
be interpreted as an unsigned integer.
In 14.10, in the new C subclauses F.10.13.2#2 and F.10.13.3#2, change:
If pl is not a positive
floating-point integer representing a valid payload, *res is set to positive
zero.
to:
If pl is not a floating-point
integer representing a valid payload, *res is set to positive zero.
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical Corrigendum
Proposed Change
In 14.10, replace the first
sentence:
IEC 60559 defines the payload of a NaN to be a certain part of the NaN’s
significand interpreted as an integer.
with:
IEC 60559 defines the payload of a NaN to be a certain part of the NaN’s
significand. The payload can be interpreted as an
unsigned integer.
In 14.10, in the new C subclause F.10.13, replace:
IEC 60559 defines the payload of a quiet or signaling NaN as an integer value encoded in the significand.
with:
IEC 60559 defines the payload of a quiet or signaling NaN as information encoded in part of the NaN significand. The payload can
be interpreted as an unsigned integer.
In 14.10, in the new C subclauses F.10.13.2#2 and F.10.13.3#2, change:
If pl is not a positive
floating-point integer representing a valid payload, *res is set to positive
zero.
to:
If pl is not a floating-point
integer representing a valid payload, *res is set to positive zero.
DR 11 Prev <— C2x —> Next DR 14, or summary at top
DR 25 Prev <— Review —> Next DR 16, or summary at top
Submitter: Jim Thomas
Submission Date: 2017-03-04
Source: WG14
Reference Document: N2125
Subject: P3: Type-generic macros for functions that round result to narrower type
Summary
This
is about an issue raised by Joseph Myers in SC22WG14.14561:
TS 18661-1 and -2 define type-generic macros for the
functions that round
result to a narrower type. In part 1 these are, for
example, fadd and
dadd for addition; in part 2, for example, d32add and
d64add.
Part
3 does not seem to make any changes or additions to those macros, and
consequences
of that seem nonobvious. It defines new functions for the
new
types: fMaddfN, fMaddfNx, fMxaddfN, fMxaddfNx (where M <
N, or M <= N
in the fMaddfNx case), and likewise for decimal types. But
the
type-generic
macros remain as defined in 7.25#6a after the changes from
parts 1
and 2 are applied (part 3 does not contain the string "6a").
That
is, it's valid to pass the _FloatN and _FloatNx types to the fadd and
dadd macros, and valid to pass the new _DecimalN and _DecimalNx types
from
part 3 to
the d32add and d64add types.
(a)
7.25#6a says "If the macro prefix is d32 or d64,
use of an argument of
standard
floating type results in undefined behavior.". Other places get
amended
in part 3 to say "floating type of radix 2" in addition to
"standard floating type". But it appears it fails
to make it undefined to
pass _FloatN or _FloatNx arguments to
d32add, d64add etc. type-generic
macros -
although clearly it should be undefined.
(b)
Passing _Decimal128 to d32add would result in the d32addd128 function
being
called, as expected. But say you pass a _Decimal128x argument. A
function
d32addd128x exists but the specification would seem to result in
d32addd64
being called, which seems unintuitive. Similar issues apply
with _FloatN and _FloatNx types -
calling fadd on them would always call
the fadd function not faddl.
(But in that case there *are* no functions
defined
that take _FloatN / _FloatNx
arguments and return float or double.
So
the right thing to do is less obvious.)
The following addresses these
issues by filling in the missing specification in part 3.
Suggested
Technical Corrigendum
In clause 15, after the change
to 7.25#6, add:
Change 7.25#6a
from:
[6a] The
functions that round result to a narrower type have type-generic macros whose
names are obtained by omitting any suffix from the function names. Thus, the
macros with f or d prefix are:
fadd
fmul
ffma
dadd
dmul
dfma
fsub
fdiv
fsqrt
dsub
ddiv
dsqrt
and the macros
with d32 or d64 prefix are:
d32add
d32mul
d32fma
d64add
d64mul
d64fma
d32sub
d32div
d32sqrt
d64sub
d64div
d64sqrt
All arguments are generic. If
any argument is not real, use of the macro results in undefined behavior. If
the macro prefix is f or d, use of an argument of decimal
floating type results in undefined behavior. If the macro prefix is d32 or d64, use of an
argument of standard floating type results in undefined behavior. The function
invoked is determined as follows:
—
If any argument has type _Decimal128, or if the
macro prefix is d64, the function
invoked has the name of the macro, with a d128 suffix.
—
Otherwise, if the macro prefix is d32, the function
invoked has the name of the macro, with a d64 suffix.
—
Otherwise, if any argument has type long double, or if the macro prefix is d, the function invoked has the name of
the macro, with an l suffix.
—
Otherwise, the function invoked has the name of the macro
(with no suffix).
to:
[6a] The functions that round
result to a narrower type have type-generic macros whose names are obtained by
omitting any suffix from the function names. Thus, the macros with f
or
d prefix are:
fadd
fmul
ffma
dadd
dmul
dfma
fsub
fdiv
fsqrt
dsub
ddiv
dsqrt
and the macros
with fM, fMx, dM, or dMx prefix are:
fMadd
fMxmul
dMfma
fMsub
fMxdiv
dMsqrt
fMmul
fMxfma dMxadd
fMdiv
fMxsqrt dMxsub
fMfma
dMadd
dMxmul
fMsqrt
dMsub
dMxdiv
fMxadd
dMmul
dMxfma
fMxsub
dMdiv
dMxsqrt
All arguments are generic. If
any argument is not real, use of the macro results in undefined behavior. If
the macro prefix is f, d, fM, or fMx, use of an argument of decimal
floating type results in undefined behavior. If the macro prefix is dM or dMx, use of an argument of standard or
binary floating type results in undefined behavior. The function invoked is
determined as follows:
— Arguments that have integer
type are regarded as having type _Decimal64 if any
argument has decimal floating type, and as having type double otherwise.
— The unsuffixed
name of the function is the name of the macro, and its suffix, if any,
corresponds to the parameter type which may be any type with at least the range
and precision of the argument types.
In clause 15, at the end of the text appended to the table
in 7.25#7, further append:
f32xadd(d, f32x) any
f32xaddfN or f32xaddfNx such that N > 32 and the suffix type, _FloatN or _FloatNx, is at least
as wide as double and _Float32x
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical Corrigendum
Apr 2018 meeting
Committee Discussion
After extensive discussion on the mailing list several documents were proposed with new and revised change suggestions. The following revised proposed change is largely drawn from N2213 with further changes reviewed at the meeting.
Proposed Change
In clause 15, after the change
to 7.25#6, add:
Change 7.25#6a
from:
[6a] The
functions that round result to a narrower type have type-generic macros whose
names are obtained by omitting any suffix from the function names. Thus, the
macros with f or d prefix are:
fadd
fmul
ffma
dadd
dmul
dfma
fsub
fdiv
fsqrt
dsub
ddiv
dsqrt
and the macros with d32 or d64 prefix are:
d32add
d32mul
d32fma
d64add
d64mul
d64fma
d32sub
d32div
d32sqrt
d64sub
d64div
d64sqrt
All arguments are generic. If
any argument is not real, use of the macro results in undefined behavior. If
the macro prefix is f or d, use of an argument of decimal
floating type results in undefined behavior. If the macro prefix is d32 or d64, use of an
argument of standard floating type results in undefined behavior. The function
invoked is determined as follows:
—
If any argument has type _Decimal128, or if the
macro prefix is d64, the function
invoked has the name of the macro, with a d128 suffix.
—
Otherwise, if the macro prefix is d32, the function
invoked has the name of the macro, with a d64 suffix.
—
Otherwise, if any argument has type long double, or if the macro prefix is d, the function invoked has the name of
the macro, with an l suffix.
—
Otherwise, the function invoked has the name of the macro
(with no suffix).
to:
[6a] The
functions that round result to a narrower type have type-generic macros whose
names are obtained by omitting any suffix from the function names. Thus, the
macros with f or d prefix are:
fadd
fmul
ffma
dadd
dmul
dfma
fsub
fdiv
fsqrt
dsub
ddiv
dsqrt
and the macros with fM, fMx, dM, or dMx prefix are:
fMadd
fMxmul
dMfma
fMsub
fMxdiv
dMsqrt
fMmul
fMxfma
dMxadd
fMdiv
fMxsqrt
dMxsub
fMfma
dMadd dMxmul
fMsqrt
dMsub dMxdiv
fMxadd dMmul dMxfma
fMxsub dMdiv dMxsqrt
All arguments are generic. If
any argument is not real, use of the macro results in undefined behavior. If
the macro prefix is f or d, use of an argument of interchange or
extended floating type results in undefined behavior. If the macro prefix is fM, or fMx, use of an argument of standard or
decimal floating type results in undefined behavior. If the macro prefix is dM or dMx, use of an argument of standard or
binary floating type results in undefined behavior. The function invoked is determined as
follows:
— Arguments that have integer type are regarded
as having type double if the macro
prefix is f or d, as having type _Float64 if the macro prefix is fM or fMx, and as having type _Decimal64 if the macro prefix is dM or dMx.
— If the function has exactly one generic
parameter, the type determined is the type of the argument.
— If the function has exactly two generic
parameters, the type determined is the type determined by the
usual arithmetic conversions (6.3.1.8) applied to the arguments.
— If the function has three generic parameters,
the type determined is the type determined by applying the usual
arithmetic conversions twice, first to the first two arguments, then to
that result type and the third argument.
— If no function with the
given prefix has the parameter type determined above, the parameter type is
determined from the prefix as follows:
f |
double |
d |
long
double |
fM |
_FloatN for minimum N > M if supported,
else _FloatMx |
fMx |
_FloatNx for minimum N > M if supported, else _FloatN for minimum N > M |
dM |
_DecimalN for minimum N > M if supported,
else _DecimalMx |
dMx |
_DecimalNx for minimum N > M if supported, else _DecimalN for minimum N > M |
In clause 15, at the end of the
text appended to the table in 7.25#7, further append:
fsub(d,
ld) fsubl
f32add(f64x, f64) f32addf64x
d32xsqrt(n) d32xsqrtd64
f32mul(f128, f32x) f32mulf128 if _Float128 is at least as wide as _Float32x, or f32mulf32x if _Float32x is
wider than _Float128
f32fma(f32x, n, f32x) f32fmaf64 if _Float64 is at least as wide as _Float32x, or f32fmaf32x if _Float32x is wider than _Float64
ddiv(ld,
f128) undefined
f32fma(f64, d, f64) undefined
fmul(dc,
d) undefined
f32add(f32, f32) f32addf64(f32, f32)
f32xsqrt(f32) f32xsqrtf64x(f32) if _Float64x is
supported,
else f32xsqrtf64
f64div(f32x, f32x) f64divf128(f32x,
f32x)
DR 25 Prev <— Review —> Next DR 16, or summary at top
DR 12 Prev <— C2x —> Next DR 15, or summary at top
Submitter: Jim Thomas
Submission Date: 2017-03-04
Source: WG14
Reference Document: N2125
Subject: P2: Effect of %a vs %A conversion specifiers
Summary
The
specification in TS 18661-2 for a,A conversion specifiers for
decimal describes the behavior in terms of
f
and e
formatting. The intention was that the A conversion specifier would
have the effects of F and E formatting. The following Technical Corrigendum
corrects this oversight, using wording similar to that in C11 for the g,G conversion specifiers.
Suggested Technical Corrigendum
In 12.5, in the text added to 7.21.6.1#8 and
7.29.2.1#8, under a,A
conversion specifiers, replace the bullets:
— if −(n+5) ≤ q ≤ 0, use style f formatting with formatting precision equal to −q,
— otherwise, use style e formatting with …
with:
— if −(n+5) ≤ q ≤ 0, use style f (or style F in the case of an A conversion specifier) with formatting precision equal to −q,
— otherwise, use style e (or style E in the case of an A conversion specifier) with …
Committee Discussion
The committee agrees that this is a defect and accepts the Suggested Technical Corrigendum
Proposed Technical Corrigendum
In 12.5, in the text added to 7.21.6.1#8 and
7.29.2.1#8, under a,A
conversion specifiers, replace the bullets:
— if −(n+5) ≤ q ≤ 0, use style f formatting with formatting precision equal to −q,
— otherwise, use style e formatting with …
with:
— if −(n+5) ≤ q ≤ 0, use style f (or style F in the case of an A conversion specifier) with formatting precision equal to −q,
— otherwise, use style e (or style E in the case of an A conversion specifier) with …
DR 12 Prev <— C2x —> Next DR 15, or summary at top
DR 14 Prev <— C2x —> Next DR 17, or summary at top
Submitter: Jim Thomas
Submission Date: 2017-10-25
Source: WG14
Reference Document: N2171
Subject: P3: Characteristic macros for non-arithmetic formats
Summary
This DR addresses an issue
related to DR 501 and IEC 60559 non-arithmetic interchange formats.
TS 18661-3 attempted to
change the definition of DECIMAL_DIG so that it would apply to all supported IEC 60559
formats. DR 501 shows that this change is problematic. After several
unsuccessful attempts at a suitable TC, WG 14 and the CFP group have agreed to
obsolesce DECIMAL_DIG in favor of the type_DECIMAL_DIG
macros.
The type_DECIMAL_DIG macros are
helpful in using conversions between binary floating-point formats and decimal
character sequences. TS 18661-3 specifies such
conversions for non-arithmetic binary interchange formats, but neglects to
include the macros for such formats.
Likewise, the type_DIG macros too are helpful in using conversions between binary floating-point formats and decimal character sequences, though TS 18661-3 does not specify them for non-arithmetic formats.
The suggested TC below extends the set of FLTN_DECIMAL_DIG and FLTN_DIG macros to include ones for IEC 60559 non-arithmetic binary interchange
formats.
Suggested Technical Corrigendum
In TS 18661-3 5.3, in the
text for 5.2.4.2.2#6c, after the list for supported types _FloatN, insert:
for IEC 60559 non-arithmetic binary interchange formats of width N:
FLTN_DECIMAL_DIG FLTN_DIG
In TS 18661-3 clause 7, in
the text for 5.2.4.2.2a#1, change:
The
prefix FLTN_ indicates a binary interchange floating type of width
N.
to:
The
prefix FLTN_ indicates a binary interchange floating type or a
non-arithmetic binary interchange format of width N.
Change the last sentence of 5.2.4.2.2a#1
from:
Conversely,
for each such type that the implementation does not provide, <float.h> shall not
define the associated macros in the following lists.
to:
Conversely,
for each such type that the implementation does not provide, <float.h> shall not
define the associated macros in the following list, except, the implementation
shall define the macros FLTN_DECIMAL_DIG and FLTN_DIG if it supports IEC 60559 non-arithmetic binary
interchange formats of width N by
providing the encoding-to-encoding conversion functions in <math.h> and the string-to-encoding and string-from-encoding
functions in <stdlib.h>.
Committee Discussion
The committee agreed with this issue and its proposed clarification.Proposed Technical Clarification
In TS 18661-3 5.3, in the
text for 5.2.4.2.2#6c, after the list for supported types _FloatN, insert:
for IEC 60559 non-arithmetic binary interchange formats of width N:
FLTN_DECIMAL_DIG FLTN_DIG
In TS 18661-3 clause 7, in
the text for 5.2.4.2.2a#1, change:
The
prefix FLTN_ indicates a binary interchange floating type of width
N.
to:
The
prefix FLTN_ indicates a binary interchange floating type or a
non-arithmetic binary interchange format of width N.
Change the last sentence of 5.2.4.2.2a#1
from:
Conversely,
for each such type that the implementation does not provide, <float.h> shall not
define the associated macros in the following lists.
to:
Conversely,
for each such type that the implementation does not provide, <float.h> shall not
define the associated macros in the following list, except, the implementation
shall define the macros FLTN_DECIMAL_DIG and FLTN_DIG if it supports IEC 60559 non-arithmetic binary
interchange formats of width N by
providing the encoding-to-encoding conversion functions in <math.h> and the string-to-encoding and string-from-encoding
functions in <stdlib.h>.
DR 14 Prev <— C2x —> Next DR 17, or summary at top
DR 13 Prev <— Review —> Next DR 20, or summary at top
Submitter: Jim Thomas
Submission Date: 2017-10-25
Source: WG14
Reference Document: N2178
Subject: P1: tgmath cbrt macro
Summary
This DR addresses a problem
noted by Joseph Myers in emails SC22WG14.14743 and 14744:
… the example [in TS 18661-1 clause 16, for 7.25#6b –
see below] implies that "#undef cbrtl" before calling the cbrt
type-generic macro would mean it's not affected by constant rounding
modes, but the actual normative text says "is affected by constant
rounding modes" with no such caveat.
and
… neither example definition [in C11 or TS 18661-1] is
valid because they might call a block-scope cbrtf
/ cbrtl; they need to avoid such a block-scope
identifier, or a macro defined by the user, while still depending on
whether expansion of the
standard header cbrtf / cbrtl
macros has been suppressed at that point.
The text in question is:
[6b] A type-generic macro corresponding to a function indicated in the table in 7.6.1a is affected by constant rounding modes (7.6.2). Note that the type-generic macro definition in the example in 6.5.1.1 does not conform to this specification. A conforming macro could be implemented as follows:
#define cbrt(X) _Generic((X), \
long double: cbrtl(X), \
default: _Roundwise_cbrt(X), \
float: cbrtf(X) \
)
where _Roundwise_cbrt() is equivalent to cbrt() invoked without macro-replacement suppression.
The cause of the problems is
the use of cbrtl and cbrtf in the macro definition. The suggested TC below
replaces these uses with _Roundwise_ prefixed identifiers
similar to _Roundwise_cbrt.
Suggested
Technical Corrigendum
In
TS 18661-1, clause 16, replace:
#define cbrt(X) _Generic((X), \
long double: cbrtl(X), \
default: _Roundwise_cbrt(X), \
float: cbrtf(X) \
)
where _Roundwise_cbrt() is equivalent to cbrt() invoked without macro-replacement suppression.
with
#define cbrt(X) _Generic((X), \
long double: _Roundwise_cbrtl(X), \
default: _Roundwise_cbrt(X), \
float: _Roundwise_cbrtf(X) \
)
where _Roundwise_cbrtl(), _Roundwise_cbrt(), and _Roundwise_cbrtf() are equivalent to cbrtl(), cbrt(), and cbrtf(),
respectively, invoked without macro-replacement suppression.
Committee Discussion
There was considerable discussion on this issue. The first point is that the _Generic example cited that is proposed to be fixed was not intended to impose requirements, yet has elicited two fixes so far, this being a third. The second point is that the fix offered would likely elicit numerous compiler errors as stated and no longer serves its original intention of illustrating _Generic best practice usage. Lastly, lacking a clear simple example, is there a problem here that needs clarification becomes uncertain.
Apr 2018 meeting
Committee Discussion
A new document N2212 was presented with a much simpler proposed change. It was accepted by the committee.
Proposed Change
In TS 18661-1, clause 16, replace:
#define cbrt(X) _Generic((X), \ long double: cbrtl(X), \ default: _Roundwise_cbrt(X), \ float: cbrtf(X) \ )
where _Roundwise_cbrt() is equivalent to cbrt() invoked without macro- replacement suppression.
with
#define cbrt(X) _Generic((X), \ long double: _Roundwise_cbrtl, \ default: _Roundwise_cbrt, \ float: _Roundwise_cbrtf \ )(X)
where _Roundwise_cbrtl(), _Roundwise_cbrt(), and _Roundwise_cbrtf() are equivalent to cbrtl(), cbrt(), and cbrtf(), respectively, invoked without macro- replacement suppression.
DR 13 Prev <— Review —> Next DR 20, or summary at top
DR 15 Prev <— C2x —> Next DR 19, or summary at top
Submitter: C Floating Point Group
Submission Date: 2018-02-11
Source: WG14
Reference Document: N2203
Subject: P3: incommensurate arguments for comparison macros
Summary
This DR addresses a problem
noted by Joseph Myers in email SC22WG14.14885:
The
usual arithmetic conversions in TS 18661-3 include "If both operands have
floating types and neither of the sets of values of their corresponding
real types is a subset of (or equivalent to) the other, the behavior is
undefined.".
Thus, for example, if neither of long double and _Float128 has a set of values
that is a subset of the other, given
long double a;
_Float128 b;
it's undefined to have the expression "a < b".
Now what about the expression "isless (a, b)"?
By analogy with the direct comparison, it would seem natural for it
to be undefined. But while 18661-2 explicitly disallows using those
macros with one decimal and one non-decimal argument, I see nothing
to disallow the case where neither set of values is a subset of the other,
and the definition of these macros doesn't actually include the usual
arithmetic conversions.
It was an oversight to not
disallow argument types neither of which is a subset (or equivalent to) the
other.
Suggested
Technical Corrigendum
In
TS 18661-3, at the end of clause 12 (just before 12.1), insert:
To 7.12.14#1, append:
If neither of the
sets of values of the argument formats is a subset of (or equivalent to)
the other, the behavior is undefined.
Apr 2018 meeting
Committee Discussion
The committee accepted the Suggested Technical Corrigendum as the Proposed Change (using our new terminology).
Proposed Change
In
TS 18661-3, at the end of clause 12 (just before 12.1), insert:
To 7.12.14#1, append:
If neither of the
sets of values of the argument formats is a subset of (or equivalent to)
the other, the behavior is undefined.
DR 15 Prev <— C2x —> Next DR 19, or summary at top
DR 18 Prev <— Closed —> Next DR 18, or summary at top
Submitter: C Floating Point Group
Submission Date: 2018-02-22
Source: WG14
Reference Document: N2204
Subject: P4: missing specification of preferred quantum exponents
Summary
TS 18661-4 neglected to
specify the preferred quantum exponent for its new functions. This was an
oversight. The following suggested TC adds the missing specification.
Suggested
Technical Corrigendum
In TS 18661-4, at the end of
clause 7, append:
In the Preferred Quantum
Exponents table in 5.2.4.2.2a#7, insert before the final row:
rsqrt |
−floor(Q(x)/2) |
compoundn |
floor(n × min(0, Q(x))) |
rootn |
floor(Q(x)/n) |
pown |
floor(n × Q(x)) |
powr |
floor(y × Q(x)) |
In TS 18661-4, at the end of
clause 8, append:
In the Preferred Exponents
Table in 5.2.4.2.2a#7, append:
reduction functions |
unspecified |
Apr 2018 meeting
Committee Discussion
The committee accepted the Suggested Technical Corrigendum as the Proposed Change (using our new terminology).
Proposed Change
In TS 18661-4, at the end of
clause 7, append:
In the Preferred Quantum
Exponents table in 5.2.4.2.2a#7, insert before the final row:
rsqrt |
−floor(Q(x)/2) |
compoundn |
floor(n × min(0, Q(x))) |
rootn |
floor(Q(x)/n) |
pown |
floor(n × Q(x)) |
powr |
floor(y × Q(x)) |
In TS 18661-4, at the end of
clause 8, append:
In the Preferred Exponents
Table in 5.2.4.2.2a#7, append:
reduction functions |
unspecified |
DR 18 Prev <— Closed —> Next DR 18, or summary at top
DR 17 Prev <— C2x —> Next DR 1, or summary at top
Submitter: C Floating Point Group
Submission Date: 2018-03-16
Source: WG14
Reference Document: N2210
Subject: P1: updating underflow definition
Summary
C11 7.12.1 says
The result underflows if the magnitude of the mathematical result is so small that the mathematical result cannot be represented, without extraordinary roundoff error, in an object of the specified type.232)232) The term underflow here is intended to encompass both ‘‘gradual underflow’’ as in IEC 60559 and also ‘‘flush-to-zero’’ underflow
The C definition of underflow doesn’t accomplish its intention as expressed in footnote 232. It’s too restrictive to encompass IEC 60559 gradual underflow, because IEC 60559 underflow can occur without extraordinary roundoff error.
In IEC 60559:2011, the underflow flag is raised (in C terminology, set) if and only if the result is tiny and inexact, even if the roundoff error is the same as it would have been if the full (normal) precision of the type were available, i.e., even if there is no extraordinary roundoff error.
IEC 60559:1989 offered the implementation the option to raise the underflow flag for tiny results with extraordinary roundoff error, though it also offered the option to raise the underflow flag for tiny inexact results, which is what most implementations did. IEC 60559:2011 dropped the option to raise the underflow flag based on extraordinary roundoff error.
The following suggested TC aims to loosens the C definition of underflow to encompass IEC 60559:2011 underflow behavior, which is based on tiny inexact results.
Suggested Technical Corrigendum
In TS 18661-1, before 14.1, insert:
14.0 C underflow
The following change to C11 loosens the C definition of underflow to encompass IEC 60559 gradual underflow, as is its stated intention (see C11 footnote 232).
Changes to C11:
Change the first sentence in 7.12.1#6 from:
[6] The result underflows if the magnitude of the mathematical result is so small that the mathematical result cannot be represented, without extraordinary roundoff error, in an object of the specified type.232) …
to:
[6] The result underflows if the magnitude of the mathematical result is nonzero and less than the minimum normal number in the type.232) …
Apr 2018 meeting
Committee Discussion
The committee accepted the Suggested Technical Corrigendum as the Proposed Change (using our new terminology).
Proposed Change
In TS 18661-1, before 14.1, insert:
14.0 C underflow
The following change to C11 loosens the C definition of underflow to encompass IEC 60559 gradual underflow, as is its stated intention (see C11 footnote 232).
Changes to C11:
Change the first sentence in 7.12.1#6 from:
[6] The result underflows if the magnitude of the mathematical result is so small that the mathematical result cannot be represented, without extraordinary roundoff error, in an object of the specified type.232) …
to:
[6] The result underflows if the magnitude of the mathematical result is nonzero and less than the minimum normal number in the type.232) …
DR 17 Prev <— C2x —> Next DR 1, or summary at top
DR 16 Prev <— Review —> Next DR 21, or summary at top
Submitter: C Floating Point Group
Submission Date: 2018-03-16
Source: WG14
Reference Document: N2211
Subject: P1: changes for obsolescing DECIMAL_DIG
Summary
N2211 described changes in C11 and TS
18661 to remove references to DECIMAL_DIG, which CR501 is
expected to obsolesce. The changes that apply to C11 are collected in N2253 as
an update to the suggested TC in CR501. The changes that apply to TS 18661-1 compose
the CR in this document. The remaining change is for TS 18661-3, which will be
covered by a CR in a subsequent document.
Suggested Technical Corrigendum
In 7.1, omit:
Change footnote 361) from:
361) If the minimum-width IEC60559 extended format (64 bits
of precision) is supported, DECIMAL_DIG shall be at
least 21. If IEC 60559 double (53 bits of precision) is the widest IEC 60559
format supported, then DECIMAL_DIG shall be at
least 17. (By contrast, LDBL_DIG and DBL_DIG are 18
and 15, respectively, for these formats.)
to:
361) If the
minimum-width IEC 60559 binary64-extended format (64 bits of precision) is
supported, DECIMAL_DIG shall be at least 21. If IEC 60559 binary64 (53 bits
of precision) is the widest IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and DBL_DIG are 18
and 15, respectively, for these formats.)
In 10.1, change:
After
F.5#2, insert:
[2a] The <float.h> header defines the macro
CR_DECIMAL_DIG
if and only if __STDC_WANT_IEC_60559_BFP_EXT__ is defined as a macro at the point in the source file
where <float.h> is first included. If defined, CR_DECIMAL_DIG expands to an integral constant expression suitable
for use in #if preprocessing directives whose
value is a number such that conversions between all supported types with IEC
60559 binary formats and character sequences with at most CR_DECIMAL_DIG significant decimal digits are correctly rounded. The
value of CR_DECIMAL_DIG shall be at least DECIMAL_DIG + 3. If
the implementation correctly rounds for all numbers of significant decimal
digits, then CR_DECIMAL_DIG shall have the
value of the macro UINTMAX_MAX.
[2b]
Conversions of types with IEC 60559 binary formats to character sequences with
more than CR_DECIMAL_DIG
significant decimal digits shall correctly round to CR_DECIMAL_DIG
significant digits and pad zeros on the right.
[2c]
Conversions from character sequences with more than CR_DECIMAL_DIG
significant decimal digits to types with IEC 60559 binary formats shall
correctly round to an intermediate character sequence with CR_DECIMAL_DIG
significant decimal digits, according to the applicable rounding direction, and
correctly round the intermediate result (having CR_DECIMAL_DIG
significant decimal digits) to the destination type. The “inexact”
floating-point exception is raised (once) if either conversion is inexact. (The
second conversion may raise the “overflow” or “underflow” floating-point
exception.)
In F.5#2c, attach a footnote to the wording:
The
“inexact” floating-point exception is raised (once) if either conversion is
inexact.
where the footnote is:
*)
The intermediate conversion is exact only if all input digits after the first CR_DECIMAL_DIG digits
are 0.
to:
Replace the content of F.5 with:
[1] The <float.h> header defines the macro
CR_DECIMAL_DIG
if and only if __STDC_WANT_IEC_60559_BFP_EXT__ is defined as a macro at the point in the source file
where <float.h> is first included. If defined, CR_DECIMAL_DIG expands to an integral constant expression suitable
for use in #if preprocessing directives whose
value is a number such that conversions between all supported IEC 60559 binary
formats and character sequences with at most CR_DECIMAL_DIG significant
decimal digits are correctly rounded. The value of CR_DECIMAL_DIG shall be at
least M + 3, where M is the maximum value of the T_DECIMAL_DIG macros
for IEC 60559 binary formats. If the implementation correctly rounds for all
numbers of significant decimal digits, then CR_DECIMAL_DIG shall
have the value of the macro UINTMAX_MAX.
[2]
Conversions of types with IEC 60559 binary formats to character sequences with
more than CR_DECIMAL_DIG
significant decimal digits shall correctly round to CR_DECIMAL_DIG
significant digits and pad zeros on the right.
[3]
Conversions from character sequences with more than CR_DECIMAL_DIG
significant decimal digits to types with IEC 60559 binary formats shall
correctly round to an intermediate character sequence with CR_DECIMAL_DIG
significant decimal digits, according to the applicable rounding direction, and
correctly round the intermediate result (having CR_DECIMAL_DIG
significant decimal digits) to the destination type. The “inexact”
floating-point exception is raised (once) if either conversion is inexact. (The
second conversion may raise the “overflow” or “underflow” floating-point
exception.)
[4] The specification in this subclause assures
conversion between IEC 60559 binary format and decimal character sequence follows
all pertinent recommended practice. It also assures conversion from IEC
60559 format to decimal character sequence with at least T_DECIMAL_DIG digits
and back, using to-nearest rounding, is the identity function, where T is the macro prefix for the format.
[5] Functions such as strtod that convert character sequences to floating types honor the rounding direction. Hence, if the rounding direction might be upward or downward, the implementation cannot convert a minus-signed sequence by negating the converted unsigned sequence.
In F.5#3, attach a footnote to the wording:
The
“inexact” floating-point exception is raised (once) if either conversion is
inexact.
where the footnote is:
*)
The intermediate conversion is exact only if all input digits after the first CR_DECIMAL_DIG digits
are 0.
Apr 2018 meeting
Committee Discussion
The paper was only briefly discussed.This resolution is tied to the Floating Point CR 22 as well as to the C2x DR 501.
Oct 2018 meeting
Committee Discussion
A new paper N2254 was split out from N2211 that incorporates directly the Suggested Technical Corrigendum already extracted above.The committee accepts the Suggested Technical Corrigendum as the Proposed Change to resolve this issue.
Proposed Change
In 7.1, omit:
Change footnote 361) from:
361) If the minimum-width IEC60559 extended format (64 bits
of precision) is supported, DECIMAL_DIG shall be at
least 21. If IEC 60559 double (53 bits of precision) is the widest IEC 60559
format supported, then DECIMAL_DIG shall be at
least 17. (By contrast, LDBL_DIG and DBL_DIG are 18
and 15, respectively, for these formats.)
to:
361) If the
minimum-width IEC 60559 binary64-extended format (64 bits of precision) is
supported, DECIMAL_DIG shall be at least 21. If IEC 60559 binary64 (53 bits
of precision) is the widest IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and DBL_DIG are 18
and 15, respectively, for these formats.)
In 10.1, change:
After
F.5#2, insert:
[2a] The <float.h> header defines the macro
CR_DECIMAL_DIG
if and only if __STDC_WANT_IEC_60559_BFP_EXT__ is defined as a macro at the point in the source file
where <float.h> is first included. If defined, CR_DECIMAL_DIG expands to an integral constant expression suitable
for use in #if preprocessing directives whose
value is a number such that conversions between all supported types with IEC
60559 binary formats and character sequences with at most CR_DECIMAL_DIG significant decimal digits are correctly rounded. The
value of CR_DECIMAL_DIG shall be at least DECIMAL_DIG + 3. If
the implementation correctly rounds for all numbers of significant decimal
digits, then CR_DECIMAL_DIG shall have the
value of the macro UINTMAX_MAX.
[2b]
Conversions of types with IEC 60559 binary formats to character sequences with
more than CR_DECIMAL_DIG
significant decimal digits shall correctly round to CR_DECIMAL_DIG
significant digits and pad zeros on the right.
[2c]
Conversions from character sequences with more than CR_DECIMAL_DIG
significant decimal digits to types with IEC 60559 binary formats shall
correctly round to an intermediate character sequence with CR_DECIMAL_DIG
significant decimal digits, according to the applicable rounding direction, and
correctly round the intermediate result (having CR_DECIMAL_DIG
significant decimal digits) to the destination type. The “inexact”
floating-point exception is raised (once) if either conversion is inexact. (The
second conversion may raise the “overflow” or “underflow” floating-point
exception.)
In F.5#2c, attach a footnote to the wording:
The
“inexact” floating-point exception is raised (once) if either conversion is
inexact.
where the footnote is:
*)
The intermediate conversion is exact only if all input digits after the first CR_DECIMAL_DIG digits
are 0.
to:
Replace the content of F.5 with:
[1] The <float.h> header defines the macro
CR_DECIMAL_DIG
if and only if __STDC_WANT_IEC_60559_BFP_EXT__ is defined as a macro at the point in the source file
where <float.h> is first included. If defined, CR_DECIMAL_DIG expands to an integral constant expression suitable
for use in #if preprocessing directives whose
value is a number such that conversions between all supported IEC 60559 binary
formats and character sequences with at most CR_DECIMAL_DIG significant
decimal digits are correctly rounded. The value of CR_DECIMAL_DIG shall be at
least M + 3, where M is the maximum value of the T_DECIMAL_DIG macros
for IEC 60559 binary formats. If the implementation correctly rounds for all
numbers of significant decimal digits, then CR_DECIMAL_DIG shall
have the value of the macro UINTMAX_MAX.
[2]
Conversions of types with IEC 60559 binary formats to character sequences with
more than CR_DECIMAL_DIG
significant decimal digits shall correctly round to CR_DECIMAL_DIG
significant digits and pad zeros on the right.
[3]
Conversions from character sequences with more than CR_DECIMAL_DIG
significant decimal digits to types with IEC 60559 binary formats shall
correctly round to an intermediate character sequence with CR_DECIMAL_DIG
significant decimal digits, according to the applicable rounding direction, and
correctly round the intermediate result (having CR_DECIMAL_DIG
significant decimal digits) to the destination type. The “inexact”
floating-point exception is raised (once) if either conversion is inexact. (The
second conversion may raise the “overflow” or “underflow” floating-point
exception.)
[4] The specification in this subclause assures
conversion between IEC 60559 binary format and decimal character sequence follows
all pertinent recommended practice. It also assures conversion from IEC
60559 format to decimal character sequence with at least T_DECIMAL_DIG digits
and back, using to-nearest rounding, is the identity function, where T is the macro prefix for the format.
[5] Functions such as strtod that convert character sequences to floating types honor the rounding direction. Hence, if the rounding direction might be upward or downward, the implementation cannot convert a minus-signed sequence by negating the converted unsigned sequence.
In F.5#3, attach a footnote to the wording:
The
“inexact” floating-point exception is raised (once) if either conversion is
inexact.
where the footnote is:
*)
The intermediate conversion is exact only if all input digits after the first CR_DECIMAL_DIG digits
are 0.
DR 16 Prev <— Review —> Next DR 21, or summary at top
DR 20 Prev <— Review —> Next DR 22, or summary at top
Submitter: C Floating Point Group
Submission Date: 2018-03-24
Source: WG14
Reference Document: N2224
Subject: P1: printf of one-digit character string
Summary
It is possible that a floating-point value, when converted to a one-digit character string, results in odd numbers no matter which way rounding is done. For roundTiesToEven, IEC 60559 specifies that the larger magnitude value be used.
Suggested Technical Corrigendum:
Add the following to TS 18661-1 clause 10.2 Conversions to character sequences:
Add to F.5 Binary-decimal conversion:
NOTE: IEC 60559 specifies that conversion to one-digit character strings using roundTiesToEven when both choices are odd, shall produce the value with the larger magnitude. This can happen with 9.5 whose nearest neighbors are 9.e0 and 1.e1, both of which are odd.
Apr 2018 meeting
Committee Discussion
The committee, once it understood the three floating values supplied, agreed with the proposed change.Subsequently, the author supplied revised values making such an understanding easier. The committee as a whole has yet to see the tweaked values presented below as the Proposed Change.
Proposed Change
Add the following to TS 18661-1 clause 10.2 Conversions to character sequences:
Add to F.5 Binary-decimal conversion:
NOTE: IEC 60559 specifies that conversion to one-digit character strings using roundTiesToEven when both choices are odd, shall produce the value with the larger magnitude. This can happen with 9.5e2 whose nearest neighbors are 9.e2 and 1.e3, both of which are odd.
Oct 2018 meeting
Committee Discussion
A new paper N2283 was presented with revised words from those suggested above in private correspondence.The committee accepts the Suggested Technical Corrigendum from that paper as the Proposed Change to resolve this issue.
Proposed Change
Add the following to TS 18661-1 clause 10.2 Conversions to character sequences:
At the end of F.5 Binary-decimal conversion, add:
NOTE IEC 60559 specifies that conversion to one-digit character strings using roundTiesToEven when both choices have an odd least significant digit, shall produce the value with the larger magnitude. For example, this can happen with 9.5e2 whose nearest neighbors are 9.e2 and 1.e3, both of which have a single odd digit in the significand part.
DR 20 Prev <— Review —> Next DR 22, or summary at top
DR 21 Prev <— Review —> Next DR 23, or summary at top
Submitter: C Floating Point Group
Submission Date: 2018-03-16
Source: WG14
Reference Document: N2211
Subject: P2: changes for obsolescing DECIMAL_DIG
Summary
N2211 described changes in C11 and TS
18661 to remove references to DECIMAL_DIG, which CR501 is
expected to obsolesce. The changes that apply to C11 are collected in N2253 as
an update to the suggested TC in CR501. The changes that apply to TS 18661-1 are
in the CR in N2254. The remaining change is for TS 18661-3, which is covered by
the CR in this document.
Suggested Technical Corrigendum
At the end of clause 7, omit:
With the
following change, DECIMAL_DIG characterizes conversions of supported IEC 60559 encodings, which may
be wider than supported floating types.
Change to C11 + TS18661-1 + TS18661-2:
In 5.2.4.2.2#11, change the bullet
defining DECIMAL_DIG
from:
— number of
decimal digits, n, such that any floating-point number in the widest
supported floating type with …
to:
— number of
decimal digits, n, such that any floating-point number in the widest of
the supported floating types and the supported IEC 60559 encodings with …
Apr 2018 meeting
Committee Discussion
The paper was only briefly discussed.This resolution is tied to the Floating Point CR 20 as well as to the C2x DR 501.
Oct 2018 meeting
Committee Discussion
A new paper N2255 was split out from N2211 that incorporates directly the Suggested Technical Corrigendum already extracted above.The committee accepts the Suggested Technical Corrigendum as the Proposed Change to resolve this issue.
Proposed Change
At the end of clause 7, omit:
With the
following change, DECIMAL_DIG characterizes conversions of supported IEC 60559 encodings, which may
be wider than supported floating types.
Change to C11 + TS18661-1 + TS18661-2:
In 5.2.4.2.2#11, change the bullet
defining DECIMAL_DIG
from:
— number of
decimal digits, n, such that any floating-point number in the widest
supported floating type with …
to:
— number of
decimal digits, n, such that any floating-point number in the widest of
the supported floating types and the supported IEC 60559 encodings with …
DR 21 Prev <— Review —> Next DR 23, or summary at top
DR 22 Prev <— Review —> Next DR 24, or summary at top
Submitter: C Floating Point Group
Submission Date: 2018-05-26
Source: WG14
Reference Document: N2262
Subject: P2: llquantexp invalid case
Summary
The llquantexp functions in 12.4.1 of TS 18661-2
compute the quantum exponent of a finite argument (of decimal floating type).
Infinities and NaNs don’t have a quantum exponent, so the description in C
7.12.11a.4 says “If x is infinite or NaN, they compute LLONG_MIN and a domain error occurs.” In similar cases, of a function with
floating parameters and integer return type, where no return value is suitable,
the “invalid” floating-point exception is raised. Examples in current C include
ilogb, lrint, and lround. However, TS 18661-2 neglects to specify raising “invalid” for llquantexp, which was an
oversight.
For the C examples above, the specification of “invalid” is in annex F,
because the functions are not just for IEC 60559 implementations. The llquantexp functions are
only for decimal floating types, which C requires to be IEC 60559 conformant.
Therefore, the specification for “invalid” can be in the primary description in
7.12.
CFP has made a similar change for the quantize functions. This was done as an editorial change, because it matches
specification for the IEC 60559 quantize operation, whose specification TS
18661 adopts by reference.
Suggested Technical Corrigendum
In TS 18661-2 12.4.1, in C 7.12.11a.4#2,
change the second sentence from:
If x is infinite or NaN, they compute LLONG_MIN and a domain error occurs.
to:
If x is infinite or NaN, they compute LLONG_MIN, the “invalid” floating-point exception is raised, and
a domain error occurs.
Oct 2018 meeting
Committee Discussion
The committee accepts the Suggested Technical Corrigendum as the Proposed Change to resolve this issue.
Proposed Change
In TS 18661-2 12.4.1, in C 7.12.11a.4#2,
change the second sentence from:
If x is infinite or NaN, they compute LLONG_MIN and a domain error occurs.
to:
If x is infinite or NaN, they compute LLONG_MIN, the “invalid” floating-point exception is raised, and
a domain error occurs.
DR 22 Prev <— Review —> Next DR 24, or summary at top
DR 23 Prev <— Review —> Next DR 25, or summary at top
Submitter: C Floating Point Group
Submission Date: 2018-06-26
Source: WG14
Reference Document: N2272
Subject: P1 remainder NaN case
Summary
The TS 18661-1 specification for
remainder in F.10.7.2, says
— remainder(x,
±∞) returns x for x not
infinite.
For x
a (quiet) NaN, this specification appears to require that the same NaN be
returned. This unintentionally goes beyond IEC 60559 whose general
specification for NaNs requires only that some (quiet) NaN be returned. The
suggested TC below uses similar words to IEC 60559’s, which allows the general
specification for NaNs to apply.
Suggested Technical Corrigendum
In TS 18661-1 clause 12, for C F.10.7.2,
change the third bullet from:
— remainder(x,
±∞) returns x for x not
infinite.
to:
— remainder(x,
±∞) returns x for finite x.
Oct 2018 meeting
Committee Discussion
The committee accepts the Suggested Technical Corrigendum as the Proposed Change to resolve this issue.
Proposed Change
In TS 18661-1 clause 12, for C F.10.7.2,
change the third bullet from:
— remainder(x,
±∞) returns x for x not
infinite.
to:
— remainder(x,
±∞) returns x for finite x.
DR 23 Prev <— Review —> Next DR 25, or summary at top
DR 24 Prev <— Review —> Next DR 13, or summary at top
Submitter: C Floating Point Group
Submission Date: 2018-09-05
Source: WG14
Reference Document: N2292
Subject: P1 totalorder parameters
Summary
The IEC 60559 totalOrder
operation provides a total ordering of the canonical members of the format,
including signaling NaNs. Therefore
the binding C function totalorder, specified in TS 18661-1, must be able
to accept signaling NaN inputs. Currently the
parameters for totalorder have floating type, whose
argument passing may convert a signaling NaN argument
into a quiet NaN parameter value. The following
suggested changes use pointers to preserve signaling NaN
inputs.
Suggested Technical Corrigendum
In
F.10.12.1 (TS 18661-1), change:
int totalorder(double
x, double y);
to:
int totalorder(double
* x, double * y);
and similarly for the other prototypes in F.10.12.1 and
F.10.12.2.
In
F.10.12.1 (TS 18661-1), change:
Description
[2] The totalorder functions determine whether the total order relationship,
defined by IEC 60559, is true for the ordered pair of its arguments x, y.
These functions are fully specified in IEC 60559. These functions are
independent of the current rounding direction mode and raise no
floating-point exceptions, even if an argument is a signaling
NaN.
Returns
[3] The totalorder functions return nonzero if and only if the total order
relation is true for the ordered pair of its arguments x, y.
to:
Description
[2] The totalorder functions determine whether the total order relationship,
defined by IEC 60559, is true for the ordered pair *x, *y.
These functions are fully specified in IEC 60559. These functions are
independent of the current rounding direction mode and raise no floating-point
exceptions, even if *x or *y is a signalling NaN.
Returns
[3] The totalorder functions return nonzero if and only if the total order
relation is true for the ordered pair *x, *y.
and similarly for F.10.12.2.
Oct 2018 meeting
Committee Discussion
The committee accepts the Suggested Technical Corrigendum as the Proposed Change to resolve this issue.
Proposed Change
In
F.10.12.1 (TS 18661-1), change:
int totalorder(double
x, double y);
to:
int totalorder(double
* x, double * y);
and similarly for the other prototypes in F.10.12.1 and
F.10.12.2.
In
F.10.12.1 (TS 18661-1), change:
Description
[2] The totalorder functions determine whether the total order relationship,
defined by IEC 60559, is true for the ordered pair of its arguments x, y.
These functions are fully specified in IEC 60559. These functions are
independent of the current rounding direction mode and raise no
floating-point exceptions, even if an argument is a signaling
NaN.
Returns
[3] The totalorder functions return nonzero if and only if the total order
relation is true for the ordered pair of its arguments x, y.
to:
Description
[2] The totalorder functions determine whether the total order relationship,
defined by IEC 60559, is true for the ordered pair *x, *y.
These functions are fully specified in IEC 60559. These functions are
independent of the current rounding direction mode and raise no floating-point
exceptions, even if *x or *y is a signalling NaN.
Returns
[3] The totalorder functions return nonzero if and only if the total order
relation is true for the ordered pair *x, *y.
and similarly for F.10.12.2.
DR 24 Prev <— Review —> Next DR 13, or summary at top