1 /* @(#)e_acosh.c 5.1 93/09/24 */
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
10 * ====================================================
13 #if defined(LIBM_SCCS) && !defined(lint)
14 static char rcsid
[] = "$NetBSD: e_acosh.c,v 1.9 1995/05/12 04:57:18 jtc Exp $";
20 * acosh(x) = log [ x + sqrt(x*x-1) ]
22 * acosh(x) := log(x)+ln2, if x is large; else
23 * acosh(x) := log(2x-1/(sqrt(x*x-1)+x)) if x>2; else
24 * acosh(x) := log1p(t+sqrt(2.0*t+t*t)); where t=x-1.
27 * acosh(x) is NaN with signal if x<1.
28 * acosh(NaN) is NaN without signal.
32 #include "math_private.h"
35 static const long double
40 ln2
= 6.93147180559945286227e-01L; /* 0x3FE62E42, 0xFEFA39EF */
43 long double __ieee754_acoshl(long double x
)
45 long double __ieee754_acoshl(x
)
52 GET_LDOUBLE_WORDS64(hx
,lx
,x
);
53 if(hx
<0x3ff0000000000000LL
) { /* x < 1 */
55 } else if(hx
>=0x41b0000000000000LL
) { /* x > 2**28 */
56 if(hx
>=0x7ff0000000000000LL
) { /* x is inf of NaN */
59 return __ieee754_logl(x
)+ln2
; /* acosh(huge)=log(2x) */
60 } else if (((hx
-0x3ff0000000000000LL
)|(lx
&0x7fffffffffffffffLL
))==0) {
61 return 0.0; /* acosh(1) = 0 */
62 } else if (hx
> 0x4000000000000000LL
) { /* 2**28 > x > 2 */
64 return __ieee754_logl(2.0*x
-one
/(x
+__ieee754_sqrtl(t
-one
)));
67 return __log1p(t
+__sqrtl(2.0*t
+t
*t
));