[Cfp-interest 3328] i suffix warning

[Jim Thomas]

I suggest that CFP propose adding a note such as the following to accompany the new specification for an imaginary suffix. Here bold indicates code typeface.

NOTE Since i suffixed constants are of complex type and have a +0 real part, their use is problematic where signed zeros and infinities are involved. For example, with ISO/IEC 60559 arithmetic,

-0.0 + 1.0i		yields	-0 + (+0 + i) =  +0 + I
-1.0i 			yields 	-(+0 + i) = -0 - I
INFINITY * 1.0i 	yields 	inf * (+0 + i) = NaN + inf i. 

The CMPLX macros in <complex.h> can be used to straightforwardly obtain particular values involving signed zeros and infinities. For example, corresponding to the cases above,

CMPLX(-0.0, 1.0) 		yields	-0 + I
CMPLX(0.0, -1.0) 		yields 	+0 - I
CMPLX(0.0, INFINITY) 	yields 	+0 + inf i


- Jim Thomas
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