1#include "libm.h"
2
3#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
4long double atanhl(long double x)
5{
6	return atanh(x);
7}
8#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
9/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */
10long double atanhl(long double x)
11{
12	union ldshape u = {x};
13	unsigned e = u.i.se & 0x7fff;
14	unsigned s = u.i.se >> 15;
15
16	/* |x| */
17	u.i.se = e;
18	x = u.f;
19
20	if (e < 0x3ff - 1) {
21		if (e < 0x3ff - LDBL_MANT_DIG/2) {
22			/* handle underflow */
23			if (e == 0)
24				FORCE_EVAL((float)x);
25		} else {
26			/* |x| < 0.5, up to 1.7ulp error */
27			x = 0.5*log1pl(2*x + 2*x*x/(1-x));
28		}
29	} else {
30		/* avoid overflow */
31		x = 0.5*log1pl(2*(x/(1-x)));
32	}
33	return s ? -x : x;
34}
35#endif
36