1#define _GNU_SOURCE
2#include "libc.h"
3#include <math.h>
4#include <stdint.h>
5
6double exp10(double x) {
7    static const double p10[] = {1e-15, 1e-14, 1e-13, 1e-12, 1e-11, 1e-10, 1e-9, 1e-8,
8                                 1e-7, 1e-6, 1e-5, 1e-4, 1e-3, 1e-2, 1e-1, 1,
9                                 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8,
10                                 1e9, 1e10, 1e11, 1e12, 1e13, 1e14, 1e15};
11    double n, y = modf(x, &n);
12    union {
13        double f;
14        uint64_t i;
15    } u = {n};
16    /* fabs(n) < 16 without raising invalid on nan */
17    if ((u.i >> 52 & 0x7ff) < 0x3ff + 4) {
18        if (!y)
19            return p10[(int)n + 15];
20        y = exp2(3.32192809488736234787031942948939 * y);
21        return y * p10[(int)n + 15];
22    }
23    return pow(10.0, x);
24}
25
26weak_alias(exp10, pow10);
27