third_party/ulib/musl/src/math/tanhf.c

#include "libm.h"

float tanhf(float x) {
    union {
        float f;
        uint32_t i;
    } u = {.f = x};
    uint32_t w;
    int sign;
    float t;

    /* x = |x| */
    sign = u.i >> 31;
    u.i &= 0x7fffffff;
    x = u.f;
    w = u.i;

    if (w > 0x3f0c9f54) {
        /* |x| > log(3)/2 ~= 0.5493 or nan */
        if (w > 0x41200000) {
            /* |x| > 10 */
            t = 1 + 0 / x;
        } else {
            t = expm1f(2 * x);
            t = 1 - 2 / (t + 2);
        }
    } else if (w > 0x3e82c578) {
        /* |x| > log(5/3)/2 ~= 0.2554 */
        t = expm1f(2 * x);
        t = t / (t + 2);
    } else if (w >= 0x00800000) {
        /* |x| >= 0x1p-126 */
        t = expm1f(-2 * x);
        t = -t / (t + 2);
    } else {
        /* |x| is subnormal */
        FORCE_EVAL(x * x);
        t = x;
    }
    return sign ? -t : t;
}