github.com/afumu/libc@v0.0.6/musl/src/math/exp10.c (about)

     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);