[Bug c/24581] New: Complex arithmetic on special cases is incorrect.

["kargl at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

/*
 * The C99 standard intends x+I*y to be used for this, but x+I*y is
 * currently unusable because gcc introduces many overflow,
 * underflow, sign and efficiency bugs by rewriting I*y as
 * (0.0+I)*(y+0.0*I) and laboriously computing the full complex product.
 * In particular, I*Inf is corrupted to NaN+I*Inf, and I*-0 is corrupted
 * to -0.0+I*0.0.
 */
#include <complex.h>
#include <math.h>
#include <stdio.h>

int main(void) {

  double complex z;
  double x, y;

  x = 0.;
  y = 1. / x;
  x = copysign(x, -1.);

  /* z = 0 + i (-0) */
  z = I * x;
  printf("%e %e\n", creal(z), cimag(z));

  /* z = 0 + i Inf */
  z = I * y;
  printf("%e %e\n", creal(z), cimag(z));

}

kargl[223] gcc -o z a.c -lm
kargl[224] ./z
-0.000000e+00 0.000000e+00
nan inf

This bug is in 3.4.4 up to an including mainline.


-- 
           Summary: Complex arithmetic on special cases is incorrect.
           Product: gcc
           Version: 3.4.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kargl at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24581