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/* from: FreeBSD: head/lib/msun/src/e_atanh.c 176451 2008-02-22 02:30:36Z das */
/* @(#)e_atanh.c 1.3 95/01/18 */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunSoft, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
/*
* See e_atanh.c for complete comments.
*
* Converted to long double by David Schultz <das@FreeBSD.ORG> and
* Bruce D. Evans.
*/
#include <float.h>
#ifdef __i386__
#include <ieeefp.h>
#endif
#include "fpmath.h"
#include "math.h"
#include "math_private.h"
/* EXP_TINY is the threshold below which we use atanh(x) ~= x. */
#if LDBL_MANT_DIG == 64
#define EXP_TINY -34
#elif LDBL_MANT_DIG == 113
#define EXP_TINY -58
#else
#error "Unsupported long double format"
#endif
#if LDBL_MAX_EXP != 0x4000
/* We also require the usual expsign encoding. */
#error "Unsupported long double format"
#endif
#define BIAS (LDBL_MAX_EXP - 1)
static const double one = 1.0, huge = 1e300;
static const double zero = 0.0;
long double
atanhl(long double x)
{
long double t;
uint16_t hx, ix;
ENTERI();
GET_LDBL_EXPSIGN(hx, x);
ix = hx & 0x7fff;
if (ix >= 0x3fff) /* |x| >= 1, or NaN or misnormal */
RETURNI(fabsl(x) == 1 ? x / zero : (x - x) / (x - x));
if (ix < BIAS + EXP_TINY && (huge + x) > zero)
RETURNI(x); /* x is tiny */
SET_LDBL_EXPSIGN(x, ix);
if (ix < 0x3ffe) { /* |x| < 0.5, or misnormal */
t = x+x;
t = 0.5*log1pl(t+t*x/(one-x));
} else
t = 0.5*log1pl((x+x)/(one-x));
RETURNI((hx & 0x8000) == 0 ? t : -t);
}
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