source:
asp3_tinet_ecnl_rx/trunk/musl-1.1.18/src/math/cosh.c
Last change on this file was 337, checked in by , 6 years ago | |
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File size: 764 bytes |
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[337] | 1 | #include "libm.h" |
2 | ||
3 | /* cosh(x) = (exp(x) + 1/exp(x))/2 | |
4 | * = 1 + 0.5*(exp(x)-1)*(exp(x)-1)/exp(x) | |
5 | * = 1 + x*x/2 + o(x^4) | |
6 | */ | |
7 | double cosh(double x) | |
8 | { | |
9 | union {double f; uint64_t i;} u = {.f = x}; | |
10 | uint32_t w; | |
11 | double t; | |
12 | ||
13 | /* |x| */ | |
14 | u.i &= (uint64_t)-1/2; | |
15 | x = u.f; | |
16 | w = u.i >> 32; | |
17 | ||
18 | /* |x| < log(2) */ | |
19 | if (w < 0x3fe62e42) { | |
20 | if (w < 0x3ff00000 - (26<<20)) { | |
21 | /* raise inexact if x!=0 */ | |
22 | FORCE_EVAL(x + 0x1p120f); | |
23 | return 1; | |
24 | } | |
25 | t = expm1(x); | |
26 | return 1 + t*t/(2*(1+t)); | |
27 | } | |
28 | ||
29 | /* |x| < log(DBL_MAX) */ | |
30 | if (w < 0x40862e42) { | |
31 | t = exp(x); | |
32 | /* note: if x>log(0x1p26) then the 1/t is not needed */ | |
33 | return 0.5*(t + 1/t); | |
34 | } | |
35 | ||
36 | /* |x| > log(DBL_MAX) or nan */ | |
37 | /* note: the result is stored to handle overflow */ | |
38 | t = __expo2(x); | |
39 | return t; | |
40 | } |
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