2 /* @(#)e_acosh.c 1.3 95/01/18 */
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
11 * ====================================================
18 * acosh(x) = log [ x + sqrt(x*x-1) ]
20 * acosh(x) := log(x)+ln2, if x is large; else
21 * acosh(x) := log(2x-1/(sqrt(x*x-1)+x)) if x>2; else
22 * acosh(x) := log1p(t+sqrt(2.0*t+t*t)); where t=x-1.
25 * acosh(x) is NaN with signal if x<1.
26 * acosh(NaN) is NaN without signal.
30 #include "math_private.h"
34 ln2 = 6.93147180559945286227e-01; /* 0x3FE62E42, 0xFEFA39EF */
42 EXTRACT_WORDS(hx,lx,x);
43 if(hx<0x3ff00000) { /* x < 1 */
45 } else if(hx >=0x41b00000) { /* x > 2**28 */
46 if(hx >=0x7ff00000) { /* x is inf of NaN */
49 return log(x)+ln2; /* acosh(huge)=log(2x) */
50 } else if(((hx-0x3ff00000)|lx)==0) {
51 return 0.0; /* acosh(1) = 0 */
52 } else if (hx > 0x40000000) { /* 2**28 > x > 2 */
54 return log(2.0*x-one/(x+sqrt(t-one)));
57 return log1p(t+sqrt(2.0*t+t*t));