src/math/ilogb.c

   1 #include <limits.h>
   2 #include "libm.h"
   3
   4 int ilogb(double x)
   5 {
   6         #pragma STDC FENV_ACCESS ON
   7         union {double f; uint64_t i;} u = {x};
   8         uint64_t i = u.i;
   9         int e = i>>52 & 0x7ff;
  10
  11         if (!e) {
  12                 i <<= 12;
  13                 if (i == 0) {
  14                         FORCE_EVAL(0/0.0f);
  15                         return FP_ILOGB0;
  16                 }
  17                 /* subnormal x */
  18                 for (e = -0x3ff; i>>63 == 0; e--, i<<=1);
  19                 return e;
  20         }
  21         if (e == 0x7ff) {
  22                 FORCE_EVAL(0/0.0f);
  23                 return i<<12 ? FP_ILOGBNAN : INT_MAX;
  24         }
  25         return e - 0x3ff;
  26 }