[Bug math/27986] New: remquo does not always set quo to a value with a negative sign when x/y has a negative sign

[Bug math/27986] New: remquo does not always set quo to a value with a negative sign when x/y has a negative sign

[vincent-srcware at vinc17 dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=27986

            Bug ID: 27986
           Summary: remquo does not always set quo to a value with a
                    negative sign when x/y has a negative sign
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: vincent-srcware at vinc17 dot net
  Target Milestone: ---

The ISO C standard says about remquo: "In the object pointed to by quo they
store a value whose sign is the sign of x/y and whose magnitude is congruent
modulo 2^n to the magnitude of the integral quotient of x/y, where n is an
implementation-defined integer greater than or equal to 3."

But when x/y has a negative sign, in some cases (at least when the mathematical
quotient is 0?), quo is not set to a value with a negative sign.

Testcase:

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

int main (void)
{
  int quo = -1;
  volatile double x = -1.0, y = 3.0;

  remquo (x, y, &quo);
  printf ("quo = %d\n", quo);
  return 0;
}

Here, x/y < 0, so that one would expect quo < 0 (as in two's complement, 0 has
a positive sign). But on my x86_64 Debian machine with GNU libc 2.31, I get:

quo = 0

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[Bug math/27986] remquo does not always set quo to a value with a negative sign when x/y has a negative sign

[vincent-srcware at vinc17 dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=27986

Vincent Lefèvre <vincent-srcware at vinc17 dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|unspecified                 |2.31

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