src/math/exp10.c

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