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67 lines
1.7 KiB
C
67 lines
1.7 KiB
C
/* s_atanhl.c -- __float128 version of s_atan.c.
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* Conversion to __float128 by Ulrich Drepper,
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* Cygnus Support, drepper@cygnus.com.
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*/
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/* atanhq(x)
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* Method :
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* 1.Reduced x to positive by atanh(-x) = -atanh(x)
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* 2.For x>=0.5
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* 1 2x x
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* atanhl(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
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* 2 1 - x 1 - x
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*
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* For x<0.5
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* atanhl(x) = 0.5*log1pl(2x+2x*x/(1-x))
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*
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* Special cases:
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* atanhl(x) is NaN if |x| > 1 with signal;
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* atanhl(NaN) is that NaN with no signal;
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* atanhl(+-1) is +-INF with signal.
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*
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*/
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#include "quadmath-imp.h"
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static const __float128 one = 1.0Q, huge = 1e4900Q;
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static const __float128 zero = 0.0Q;
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__float128
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atanhq (__float128 x)
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{
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__float128 t;
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uint32_t jx, ix;
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ieee854_float128 u;
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u.value = x;
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jx = u.words32.w0;
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ix = jx & 0x7fffffff;
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u.words32.w0 = ix;
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if (ix >= 0x3fff0000) /* |x| >= 1.0 or infinity or NaN */
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{
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if (u.value == one)
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return x/zero;
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else
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return (x-x)/(x-x);
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}
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if(ix<0x3fc60000 && (huge+x)>zero) return x; /* x < 2^-57 */
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if(ix<0x3ffe0000) { /* x < 0.5 */
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t = u.value+u.value;
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t = 0.5*log1pq(t+t*u.value/(one-u.value));
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} else
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t = 0.5*log1pq((u.value+u.value)/(one-u.value));
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if(jx & 0x80000000) return -t; else return t;
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}
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