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Here's some minimal failing code.
// Compile with:
// gcc-4.4 -m64 -fno-inline -g -O3 copysign_bug.c -o copysign_bug
#include <math.h>
#include <stdio.h>
int copysign_bug(double x)
{
 if (x && (x * 0.5 == x))
 return 1;
 if (copysign(1.0, x) < 0.0)
 return 2;
 else
 return 3;
}
int main(void) {
 double x;
 x = -0.0;
 printf("copysign_bug(%.17g) = %d\n", x, copysign_bug(x));
 x = 0.0;
 printf("copysign_bug(%.17g) = %d\n", x, copysign_bug(x));
 return 0;
}
This produces the output:
copysign_bug(-0) = 3
copysign_bug(0) = 3
I would expecting to see:
copysign_bug(-0) = 2
copysign_bug(0) = 3
I've reported this at:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44683