libc-top-half/musl/src/math/modf.c

   1 #include "libm.h"
   2
   3 double modf(double x, double *iptr)
   4 {
   5         union {double f; uint64_t i;} u = {x};
   6         uint64_t mask;
   7         int e = (int)(u.i>>52 & 0x7ff) - 0x3ff;
   8
   9         /* no fractional part */
  10         if (e >= 52) {
  11                 *iptr = x;
  12                 if (e == 0x400 && u.i<<12 != 0) /* nan */
  13                         return x;
  14                 u.i &= 1ULL<<63;
  15                 return u.f;
  16         }
  17
  18         /* no integral part*/
  19         if (e < 0) {
  20                 u.i &= 1ULL<<63;
  21                 *iptr = u.f;
  22                 return x;
  23         }
  24
  25         mask = -1ULL>>12>>e;
  26         if ((u.i & mask) == 0) {
  27                 *iptr = x;
  28                 u.i &= 1ULL<<63;
  29                 return u.f;
  30         }
  31         u.i &= ~mask;
  32         *iptr = u.f;
  33         return x - u.f;
  34 }