#include "libm.h"/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */double atanh(double x){union {double f; uint64_t i;} u = {.f = x};unsigned e = u.i >> 52 & 0x7ff;unsigned s = u.i >> 63;double_t y;/* |x| */u.i &= (uint64_t)-1/2;y = u.f;if (e < 0x3ff - 1) {if (e < 0x3ff - 32) {/* handle underflow */if (e == 0)FORCE_EVAL((float)y);} else {/* |x| < 0.5, up to 1.7ulp error */y = 0.5*log1p(2*y + 2*y*y/(1-y));}} else {/* avoid overflow */y = 0.5*log1p(2*(y/(1-y)));}return s ? -y : y;}