| #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 |
