exp10.c raw

   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);
  25