1 2 /* @(#)e_acosh.c 1.3 95/01/18 */ 3 /* 4 * ==================================================== 5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 6 * 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 10 * is preserved. 11 * ==================================================== 12 * 13 */ 14 15 #include "cdefs-compat.h" 16 //__FBSDID("$FreeBSD: src/lib/msun/src/e_acosh.c,v 1.9 2008/02/22 02:30:34 das Exp $"); 17 18 /* __ieee754_acosh(x) 19 * Method : 20 * Based on 21 * acosh(x) = log [ x + sqrt(x*x-1) ] 22 * we have 23 * acosh(x) := log(x)+ln2, if x is large; else 24 * acosh(x) := log(2x-1/(sqrt(x*x-1)+x)) if x>2; else 25 * acosh(x) := log1p(t+sqrt(2.0*t+t*t)); where t=x-1. 26 * 27 * Special cases: 28 * acosh(x) is NaN with signal if x<1. 29 * acosh(NaN) is NaN without signal. 30 */ 31 32 #include "openlibm.h" 33 #include "math_private.h" 34 35 static const double 36 one = 1.0, 37 ln2 = 6.93147180559945286227e-01; /* 0x3FE62E42, 0xFEFA39EF */ 38 39 DLLEXPORT double 40 __ieee754_acosh(double x) 41 { 42 double t; 43 int32_t hx; 44 u_int32_t lx; 45 EXTRACT_WORDS(hx,lx,x); 46 if(hx<0x3ff00000) { /* x < 1 */ 47 return (x-x)/(x-x); 48 } else if(hx >=0x41b00000) { /* x > 2**28 */ 49 if(hx >=0x7ff00000) { /* x is inf of NaN */ 50 return x+x; 51 } else 52 return __ieee754_log(x)+ln2; /* acosh(huge)=log(2x) */ 53 } else if(((hx-0x3ff00000)|lx)==0) { 54 return 0.0; /* acosh(1) = 0 */ 55 } else if (hx > 0x40000000) { /* 2**28 > x > 2 */ 56 t=x*x; 57 return __ieee754_log(2.0*x-one/(x+sqrt(t-one))); 58 } else { /* 1<x<2 */ 59 t = x-one; 60 return log1p(t+sqrt(2.0*t+t*t)); 61 } 62 } 63