| |
| /* |
| * Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* __ieee754_acosh(x) |
| * Method : |
| * Based on |
| * acosh(x) = log [ x + sqrt(x*x-1) ] |
| * we have |
| * acosh(x) := log(x)+ln2, if x is large; else |
| * acosh(x) := log(2x-1/(sqrt(x*x-1)+x)) if x>2; else |
| * acosh(x) := log1p(t+sqrt(2.0*t+t*t)); where t=x-1. |
| * |
| * Special cases: |
| * acosh(x) is NaN with signal if x<1. |
| * acosh(NaN) is NaN without signal. |
| */ |
| |
| #include "fdlibm.h" |
| |
| #ifdef __STDC__ |
| static const double |
| #else |
| static double |
| #endif |
| one = 1.0, |
| ln2 = 6.93147180559945286227e-01; /* 0x3FE62E42, 0xFEFA39EF */ |
| |
| #ifdef __STDC__ |
| double __ieee754_acosh(double x) |
| #else |
| double __ieee754_acosh(x) |
| double x; |
| #endif |
| { |
| double t; |
| int hx; |
| hx = __HI(x); |
| if(hx<0x3ff00000) { /* x < 1 */ |
| return (x-x)/(x-x); |
| } else if(hx >=0x41b00000) { /* x > 2**28 */ |
| if(hx >=0x7ff00000) { /* x is inf of NaN */ |
| return x+x; |
| } else |
| return __ieee754_log(x)+ln2; /* acosh(huge)=log(2x) */ |
| } else if(((hx-0x3ff00000)|__LO(x))==0) { |
| return 0.0; /* acosh(1) = 0 */ |
| } else if (hx > 0x40000000) { /* 2**28 > x > 2 */ |
| t=x*x; |
| return __ieee754_log(2.0*x-one/(x+sqrt(t-one))); |
| } else { /* 1<x<2 */ |
| t = x-one; |
| return log1p(t+sqrt(2.0*t+t*t)); |
| } |
| } |
