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/**
* This file has no copyright assigned and is placed in the Public Domain.
* This file is part of the mingw-w64 runtime package.
* No warranty is given; refer to the file DISCLAIMER.PD within this package.
*/
#include <math.h>
#include <errno.h>
#include "fastmath.h"
/* atanh (x) = 0.5 * log ((1.0 + x)/(1.0 - x)) */
long double atanhl (long double x)
{
long double z;
if (isnan (x))
return x;
z = fabsl (x);
if (z == 1.0L)
{
errno = ERANGE;
return (x > 0 ? INFINITY : -INFINITY);
}
if ( z > 1.0L)
{
errno = EDOM;
return nanl("");
}
/* Rearrange formula to avoid precision loss for small x.
atanh(x) = 0.5 * log ((1.0 + x)/(1.0 - x))
= 0.5 * log1p ((1.0 + x)/(1.0 - x) - 1.0)
= 0.5 * log1p ((1.0 + x - 1.0 + x) /(1.0 - x))
= 0.5 * log1p ((2.0 * x ) / (1.0 - x)) */
z = 0.5L * __fast_log1pl ((z + z) / (1.0L - z));
return x >= 0 ? z : -z;
}
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