newlib/libc/stdlib/__exp10.c

   1 /*
   2  * compute 10**x by successive squaring.
   3  */
   4
   5 #include <_ansi.h>
   6 #include "std.h"
   7
   8 double
   9 __exp10 (unsigned x)
  10 {
  11   static const double powtab[] =
  12   {1.0,
  13    10.0,
  14    100.0,
  15    1000.0,
  16    10000.0};
  17
  18   if (x < (sizeof (powtab) / sizeof (double)))
  19       return powtab[x];
  20   else if (x & 1)
  21     {
  22       return 10.0 * __exp10 (x - 1);
  23     }
  24   else
  25     {
  26       double n = __exp10 (x / 2);
  27       return n * n;
  28     }
  29 }