1#include "libm.h"
2
3#if FLT_EVAL_METHOD == 2
4#undef sqrtf
5#define sqrtf sqrtl
6#elif FLT_EVAL_METHOD == 1
7#undef sqrtf
8#define sqrtf sqrt
9#endif
10
11/* acosh(x) = log(x + sqrt(x*x-1)) */
12float acoshf(float x) {
13    union {
14        float f;
15        uint32_t i;
16    } u = {x};
17    uint32_t a = u.i & 0x7fffffff;
18
19    if (a < 0x3f800000 + (1 << 23)) /* |x| < 2, invalid if x < 1 or nan */
20        /* up to 2ulp error in [1,1.125] */
21        return log1pf(x - 1 + sqrtf((x - 1) * (x - 1) + 2 * (x - 1)));
22    if (a < 0x3f800000 + (12 << 23)) /* |x| < 0x1p12 */
23        return logf(2 * x - 1 / (x + sqrtf(x * x - 1)));
24    /* x >= 0x1p12 */
25    return logf(x) + 0.693147180559945309417232121458176568f;
26}
27