20200605.check-x87-fsin.c

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

int
main (void)
{
  long double x = 2646693125139304345;
  printf("input:\n\t%La = %.19Le\n", x, x);
  long double t = 1.188488579586842482197671275325e-20L;
  printf("mathematically correct value:\n\t%La = %.19Le\n", t, t);
  long double y = sinl(x);
  printf("computed by sinl:\n\t%La = %.19Le\n", y, y);
  long double z;
  asm("fsin" : "=t" (z) : "0" (x));
  printf("computed by x87 fsin:\n\t%La = %.19Le\n", z, z);
  return 0;
}

20200605.check-x87-fsin.out

input:
	0x9.2ebc57f85963e64p+58 = 2.6466931251393043450e+18
mathematically correct value:
	0xe.07fc7fd31b3447ap-70 = 1.1884885795868424822e-20
computed by sinl:
	0xe.07fc7fd31b3447ap-70 = 1.1884885795868424822e-20
computed by x87 fsin:
	-0xd.f4e6f150a65fdf3p-12 = -3.4073849865677573455e-03