Issue 0EMB.02: Order in which overflow handling and rounding is done

This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.

Authors: WG14
Date: 2004-09-23
Reference document: Embedded-c email list 208
Submitted against: Embedded C TR 18037:2004
Status: Fixed
Fixed in: Embedded C TR 18037:2008
Converted from: n1071.pdf, n1087.pdf, n1180.pdf

Description: the current text requires that overflow handling is done before rounding; this is counter intuitive, and not what is done for floating-point overflow/rounding. As it happens, the order in which overflow and rounding are done has no effect on the result when saturation is used for overflow handling.

Hence, if we change the order, the result remains the same for saturation. However, with the current required order, mod_wrap as overflow handling (which is allowed but not required) cannot (reasonably) be implemented. It is therefore proposed to change the order.

Proposed solution: change the required order of overflow handling and rounding.

Comment from WG14 on 2004-11-15:

Problem: TR 18037 requires that overflow handling be done before rounding, which causes problems for alternative overflow modes such as modular wraparound. (When the overflow mode is saturation, the order in which rounding and overflow handling are performed has no effect on the end-result.)

Solution: Specify that rounding should be done before overflow handling.

Changes:

• Clause 4.1.3, para 3: strike '(after any overflow handling)'.
• Replacement text for 5.2.4.2.3:
  • Replace in para 6 (staring with 'If the result type of an arithmetic operation') the text 'and then overflow handling and rounding' by 'and then rounding and overflow handling'
  • Strike from para 9 (starting with 'If (after any overflow handling)') the text '(after any overflow handling)'