[Bug math/18238] New: quality of implementation: fmin and fmax should handle signed zeros

["nszabolcs at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=18238

            Bug ID: 18238
           Summary: quality of implementation: fmin and fmax should handle
                    signed zeros
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: nszabolcs at gmail dot com

ISO C with Annex F seems to allow the result of fmax and fmin to have arbitrary
sign when the arguments are zeros, but ideally the sign should be handled
because these functions are supposed to have exact result.

http://port70.net/~nsz/c/c11/n1570.html#F.10.9.2

the code below outputs:

fmax(0, -0.0) signbit is not 0
fmaxf(0, -0.0f) signbit is not 0
fmaxl(-0.0L, 0) signbit is not 0
fmin(-0.0, 0) signbit is not 1
fminf(-0.0f, 0) signbit is not 1
fminl(0, -0.0L) signbit is not 1


#include <math.h>
#include <stdio.h>

#define T(f,s) if (signbit(f) != s) printf(#f " signbit is not " #s "\n");

int main()
{
T(fmax(0, -0.0), 0)
T(fmaxf(0, -0.0f), 0)
T(fmaxl(-0.0L, 0), 0)
T(fmin(-0.0, 0), 1)
T(fminf(-0.0f, 0), 1)
T(fminl(0, -0.0L), 1)
}

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