#include "libm.h"

#if FLT_EVAL_METHOD == 2
#undef sqrtf
#define sqrtf sqrtl
#elif FLT_EVAL_METHOD == 1
#undef sqrtf
#define sqrtf sqrt
#endif

/* acosh(x) = log(x + sqrt(x*x-1)) */
float acoshf(float x) {
    union {
        float f;
        uint32_t i;
    } u = {x};
    uint32_t a = u.i & 0x7fffffff;

    if (a < 0x3f800000 + (1 << 23)) /* |x| < 2, invalid if x < 1 or nan */
        /* up to 2ulp error in [1,1.125] */
        return log1pf(x - 1 + sqrtf((x - 1) * (x - 1) + 2 * (x - 1)));
    if (a < 0x3f800000 + (12 << 23)) /* |x| < 0x1p12 */
        return logf(2 * x - 1 / (x + sqrtf(x * x - 1)));
    /* x >= 0x1p12 */
    return logf(x) + 0.693147180559945309417232121458176568f;
}