src/math/exp10.c

   1 #define _GNU_SOURCE
   2 #include <math.h>
   3 #include <stdint.h>
   4 #include "libc.h"
   5
   6 double exp10(double x)
   7 {
   8         static const double p10[] = {
   9                 1e-15, 1e-14, 1e-13, 1e-12, 1e-11, 1e-10,
  10                 1e-9, 1e-8, 1e-7, 1e-6, 1e-5, 1e-4, 1e-3, 1e-2, 1e-1,
  11                 1, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
  12                 1e10, 1e11, 1e12, 1e13, 1e14, 1e15
  13         };
  14         double n, y = modf(x, &n);
  15         union {double f; uint64_t i;} u = {n};
  16         /* fabs(n) < 16 without raising invalid on nan */
  17         if ((u.i>>52 & 0x7ff) < 0x3ff+4) {
  18                 if (!y) return p10[(int)n+15];
  19                 y = exp2(3.32192809488736234787031942948939 * y);
  20                 return y * p10[(int)n+15];
  21         }
  22         return pow(10.0, x);
  23 }
  24
  25 weak_alias(exp10, pow10);