src/math/scalbn.c

   1 #include <math.h>
   2 #include <stdint.h>
   3
   4 double scalbn(double x, int n)
   5 {
   6         union {double f; uint64_t i;} u;
   7         double_t y = x;
   8
   9         if (n > 1023) {
  10                 y *= 0x1p1023;
  11                 n -= 1023;
  12                 if (n > 1023) {
  13                         y *= 0x1p1023;
  14                         n -= 1023;
  15                         if (n > 1023)
  16                                 n = 1023;
  17                 }
  18         } else if (n < -1022) {
  19                 /* make sure final n < -53 to avoid double
  20                    rounding in the subnormal range */
  21                 y *= 0x1p-1022 * 0x1p53;
  22                 n += 1022 - 53;
  23                 if (n < -1022) {
  24                         y *= 0x1p-1022 * 0x1p53;
  25                         n += 1022 - 53;
  26                         if (n < -1022)
  27                                 n = -1022;
  28                 }
  29         }
  30         u.i = (uint64_t)(0x3ff+n)<<52;
  31         x = y * u.f;
  32         return x;
  33 }