### view libquadmath/math/acoshq.c @ 158:494b0b89df80defaulttip

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author Shinji KONO Mon, 25 May 2020 18:13:55 +0900 1830386684a0
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```
/* e_acoshl.c -- long double version of e_acosh.c.
* Conversion to long double by Jakub Jelinek, jj@ultra.linux.cz.
*/

/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/

/* acoshq(x)
* Method :
*	Based on
*		acoshl(x) = logq [ x + sqrtq(x*x-1) ]
*	we have
*		acoshl(x) := logq(x)+ln2,	if x is large; else
*		acoshl(x) := logq(2x-1/(sqrtq(x*x-1)+x)) if x>2; else
*		acoshl(x) := log1pq(t+sqrtq(2.0*t+t*t)); where t=x-1.
*
* Special cases:
*	acoshl(x) is NaN with signal if x<1.
*	acoshl(NaN) is NaN without signal.
*/

#include "quadmath-imp.h"

static const __float128
one	= 1.0,
ln2	= 0.6931471805599453094172321214581766Q;

__float128
acoshq(__float128 x)
{
__float128 t;
uint64_t lx;
int64_t hx;
GET_FLT128_WORDS64(hx,lx,x);
if(hx<0x3fff000000000000LL) {		/* x < 1 */
return (x-x)/(x-x);
} else if(hx >=0x4035000000000000LL) {	/* x > 2**54 */
if(hx >=0x7fff000000000000LL) {	/* x is inf of NaN */
return x+x;
} else
return logq(x)+ln2;	/* acoshl(huge)=logq(2x) */
} else if(((hx-0x3fff000000000000LL)|lx)==0) {
return 0;			/* acosh(1) = 0 */
} else if (hx > 0x4000000000000000LL) {	/* 2**28 > x > 2 */
t=x*x;
return logq(2*x-one/(x+sqrtq(t-one)));
} else {			/* 1<x<2 */
t = x-one;
return log1pq(t+sqrtq(2*t+t*t));
}
}
```