[Bug math/16708] New: sin () gets wrong answer on Sempron 145

["warshall at 99main dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16708

            Bug ID: 16708
           Summary: sin () gets wrong answer on Sempron 145
           Product: glibc
           Version: 2.19
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: warshall at 99main dot com

The sin() call gives wrong results for some (fortunately rare) input values.
To replicate:

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

int main (int argc, char **argv) {
  double x = atof (argv[1]);
  printf ("x = %.30g aka %a\n", x, x);
  printf ("sin (x) = %g\n", sin (x));
  printf ("sin (x-2pi) = %g\n", sin (x-2*M_PI));
  return 0;
}

Compile with:
gcc -Wall -O2 -march=amdfam10 <name of file> -lm

 ./a.out 24985672148.49707

Output is:

x = 24985672148.4970703125 aka 0x1.7450c6751fdp+34
sin (x) = 0.552665
sin (x-2pi) = -0.552664

which is obviously wrong, since the two answers should be the same (mod
roundoff error from the finite precision of computing x-2*M_PI)

I don't think this is a duplicate of
https://sourceware.org/bugzilla/show_bug.cgi?id=16625, since

./a.out 12.3

behaves sensibly on my system. However, my glibc was compiled with gcc 4.8.2.

This bug gives rise to https://bugzilla.gnome.org/show_bug.cgi?id=726250 on
gnumeric.

                                -Andrew Warshall

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