[bug libm] bug cos/sin de la librairie math (libc6)

sin(2*pi*0.27*7390843)   =  -0.63742399  OK
sin(2*pi*2.27*7390843)   =   0.63742398  KO

cos(2*pi*0.27*7390879)   =  -0.48175367  OK
cos(2*pi*2.27*7390879)   =   0.48175367  KO

/*
 * Bug cos() & sin() dans libc6 (libm) ubuntu 14.04
 * C'est un bug de la version 2.19 de eglibc (qui contient libc6 et libm)
 */

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

#define PRECISION   1e-5

void bug_cos(void)
{
  int        n;
  double     c1,c2,s1,s2;
  int        nerr  = 0;

  for (n = 0; n < 10000000; n++)
  {

    /* si pas d'erreur c1 = c2 et s1 = s2 */
    c1 = cos(2. * M_PI * 0.27 * (double) n);
    c2 = cos(2. * M_PI * 2.27 * (double) n);
    s1 = sin(2. * M_PI * 0.27 * (double) n);
    s2 = sin(2. * M_PI * 2.27 * (double) n);

    /* si |c2 - c1| > PRECISION */
    if (fabs(c2-c1) > PRECISION)
    {
      fprintf(stdout,
          "ERR:\n"
          "      cos(2*pi*0.27*%d)         = %12.8f  OK\n"
          "      cos(2*pi*2.27*%d)         = %12.8f  KO\n",
          n,c1,n,c2);

      nerr++;
    }

    /* si |s2 - s1| > PRECISION */
    if (fabs(s2-s1) > PRECISION)
    {
      fprintf(stdout,
          "ERR:\n"
          "      sin(2*pi*0.27*%d)         = %12.8f  OK\n"
          "      sin(2*pi*2.27*%d)         = %12.8f  KO\n",
          n,s1,n,s2);

      nerr++;
    }

    /* n'affiche que les premieres erreurs ... */
    if (nerr > 4)
    {
      fprintf(stdout,"ERR : ...\n\n");
      break;
    }

  }
}

int main(int na, char *arg[])
{
  bug_cos();

  return 0;
}