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1 | /* @(#)e_acosh.c 5.1 93/09/24 */ |
2 | /* | |
3 | * ==================================================== | |
4 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. | |
5 | * | |
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 | |
9 | * is preserved. | |
10 | * ==================================================== | |
11 | */ | |
12 | ||
f964490f RM |
13 | /* __ieee754_acosh(x) |
14 | * Method : | |
15 | * Based on | |
16 | * acosh(x) = log [ x + sqrt(x*x-1) ] | |
17 | * we have | |
18 | * acosh(x) := log(x)+ln2, if x is large; else | |
19 | * acosh(x) := log(2x-1/(sqrt(x*x-1)+x)) if x>2; else | |
20 | * acosh(x) := log1p(t+sqrt(2.0*t+t*t)); where t=x-1. | |
21 | * | |
22 | * Special cases: | |
23 | * acosh(x) is NaN with signal if x<1. | |
24 | * acosh(NaN) is NaN without signal. | |
25 | */ | |
26 | ||
1ed0291c RH |
27 | #include <math.h> |
28 | #include <math_private.h> | |
f964490f | 29 | |
f964490f | 30 | static const long double |
f964490f | 31 | one = 1.0L, |
396e3ecf | 32 | ln2 = M_LN2l; |
f964490f | 33 | |
0ac5ae23 UD |
34 | long double |
35 | __ieee754_acoshl(long double x) | |
f964490f RM |
36 | { |
37 | long double t; | |
38 | int64_t hx; | |
4ebd120c AM |
39 | uint64_t lx; |
40 | double xhi, xlo; | |
41 | ||
42 | ldbl_unpack (x, &xhi, &xlo); | |
43 | EXTRACT_WORDS64 (hx, xhi); | |
44 | EXTRACT_WORDS64 (lx, xlo); | |
f964490f RM |
45 | if(hx<0x3ff0000000000000LL) { /* x < 1 */ |
46 | return (x-x)/(x-x); | |
440169d6 | 47 | } else if(hx >=0x4370000000000000LL) { /* x >= 2**56 */ |
f964490f | 48 | if(hx >=0x7ff0000000000000LL) { /* x is inf of NaN */ |
0ac5ae23 | 49 | return x+x; |
f964490f RM |
50 | } else |
51 | return __ieee754_logl(x)+ln2; /* acosh(huge)=log(2x) */ | |
52 | } else if (((hx-0x3ff0000000000000LL)|(lx&0x7fffffffffffffffLL))==0) { | |
53 | return 0.0; /* acosh(1) = 0 */ | |
440169d6 | 54 | } else if (hx > 0x4000000000000000LL) { /* 2**56 > x > 2 */ |
f964490f RM |
55 | t=x*x; |
56 | return __ieee754_logl(2.0*x-one/(x+__ieee754_sqrtl(t-one))); | |
57 | } else { /* 1<x<2 */ | |
58 | t = x-one; | |
396e3ecf | 59 | return __log1pl(t+__ieee754_sqrtl(2.0*t+t*t)); |
f964490f RM |
60 | } |
61 | } | |
0ac5ae23 | 62 | strong_alias (__ieee754_acoshl, __acoshl_finite) |