64 lines
1.7 KiB
C
64 lines
1.7 KiB
C
/* @(#)e_acosh.c 5.1 93/09/24 */
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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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/* __ieee754_acosh(x)
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* Method :
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* Based on
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* acosh(x) = log [ x + sqrt(x*x-1) ]
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* we have
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* acosh(x) := log(x)+ln2, if x is large; else
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* acosh(x) := log(2x-1/(sqrt(x*x-1)+x)) if x>2; else
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* acosh(x) := log1p(t+sqrt(2.0*t+t*t)); where t=x-1.
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*
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* Special cases:
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* acosh(x) is NaN with signal if x<1.
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* acosh(NaN) is NaN without signal.
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*/
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#include <math.h>
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#include <math_private.h>
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#include <libm-alias-finite.h>
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static const long double
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one = 1.0L,
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ln2 = M_LN2l;
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long double
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__ieee754_acoshl(long double x)
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{
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long double t;
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int64_t hx;
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uint64_t lx;
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double xhi, xlo;
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ldbl_unpack (x, &xhi, &xlo);
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EXTRACT_WORDS64 (hx, xhi);
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EXTRACT_WORDS64 (lx, xlo);
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if(hx<0x3ff0000000000000LL) { /* x < 1 */
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return (x-x)/(x-x);
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} else if(hx >=0x4370000000000000LL) { /* x >= 2**56 */
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if(hx >=0x7ff0000000000000LL) { /* x is inf of NaN */
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return x+x;
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} else
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return __ieee754_logl(x)+ln2; /* acosh(huge)=log(2x) */
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} else if (((hx-0x3ff0000000000000LL)|(lx&0x7fffffffffffffffLL))==0) {
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return 0.0; /* acosh(1) = 0 */
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} else if (hx > 0x4000000000000000LL) { /* 2**56 > x > 2 */
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t=x*x;
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return __ieee754_logl(2.0*x-one/(x+sqrtl(t-one)));
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} else { /* 1<x<2 */
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t = x-one;
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return __log1pl(t+sqrtl(2.0*t+t*t));
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}
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}
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libm_alias_finite (__ieee754_acoshl, __acoshl)
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