WG14/N818 J11/98-017 Creating complex numbers. How to build a complex number in C9X (or what happens if an implementation supports NaNs and has I be of type float complex)? Note: in the following, treat as an italic i, meaning the mathematical i for the sqrt(-1). Currently, the draft suggests (page 257, footnote 188) that a complex number z should compare equal to creal(z) + cimag(z)*I; but this is not the same as saying a complex number can be built up from two reals, say x and y, by doing the expression: (x+y*I). For example, if I is defined to be of type complex (instead of type imaginary) and y is a NaN, (x+y*I) need not be the same as x+y*. If I is of type complex (instead of imaginary), there is a problem. The problem is: I*NaN is NaN+NaN*, instead of the expected 0+NaN*, so, the sum x+I*y ends up being NaN+NaN*, instead of the expected x+NaN*. The draft states (6.1.2.5 Types, page 40) that the first element of complex is the real part and that the second element is the imaginary part and that complex have the alignment and representation as an array of two real elements. Some proposed solutions: 1) Allow access to the components of a complex variable (as if it were a structure with members re and im). That is, allow one to write: z.re = x; z.im = y; 2) Allow access to the components of a complex variable (as if it were an array of two elements). That is, allow one to write: z[0] = x; or maybe z.[0] = x; z[1] = y; z.[1] = y; 3) Create a macro of the form: z = CMPLX( x, y ); to create a complex number from two real numbers and where it is understood that the first argument to the macro is the real component and the second argument is the imaginary component. 4) Define, by fiat, I*y to treat the real part as if it were (negative) zero, even if I is of type complex. We believe that this only matters if y is a NaN. The negative zero is required if directed rounding is supported and is the value required to have -0 + -0 be -0 in any rounding mode in IEC 559. 5) Allow compound literals of the form: z = (double complex){ x, y }; where it is understood that the first element of the compound literal is the real component and the second element is the imaginary component. The current C9X draft may already allow this in section (6.2.3.5 Compound Literals, pages 76-79). 6) Allow in initialization lists, pairs of numbers: double complex z = {x, y}; to be used, as if a two element array (or a structure with two elements) were being initialized, with the first number being the real and the second number being the imaginary. 7) Do nothing. Any others?