#include "libm.h"

#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
long double atanhl(long double x) {
    return atanh(x);
}
#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */
long double atanhl(long double x) {
    union ldshape u = {x};
    unsigned e = u.i.se & 0x7fff;
    unsigned s = u.i.se >> 15;

    /* |x| */
    u.i.se = e;
    x = u.f;

    if (e < 0x3ff - 1) {
        if (e < 0x3ff - LDBL_MANT_DIG / 2) {
            /* handle underflow */
            if (e == 0)
                FORCE_EVAL((float)x);
        } else {
            /* |x| < 0.5, up to 1.7ulp error */
            x = 0.5 * log1pl(2 * x + 2 * x * x / (1 - x));
        }
    } else {
        /* avoid overflow */
        x = 0.5 * log1pl(2 * (x / (1 - x)));
    }
    return s ? -x : x;
}
#endif