source:
EcnlProtoTool/trunk/musl-1.1.18/src/math/acoshf.c
Last change on this file was 444, checked in by , 4 years ago | |
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File size: 605 bytes |
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1 | #include "libm.h" |
2 | |
3 | #if FLT_EVAL_METHOD==2 |
4 | #undef sqrtf |
5 | #define sqrtf sqrtl |
6 | #elif FLT_EVAL_METHOD==1 |
7 | #undef sqrtf |
8 | #define sqrtf sqrt |
9 | #endif |
10 | |
11 | /* acosh(x) = log(x + sqrt(x*x-1)) */ |
12 | float acoshf(float x) |
13 | { |
14 | union {float f; uint32_t i;} u = {x}; |
15 | uint32_t a = u.i & 0x7fffffff; |
16 | |
17 | if (a < 0x3f800000+(1<<23)) |
18 | /* |x| < 2, invalid if x < 1 or nan */ |
19 | /* up to 2ulp error in [1,1.125] */ |
20 | return log1pf(x-1 + sqrtf((x-1)*(x-1)+2*(x-1))); |
21 | if (a < 0x3f800000+(12<<23)) |
22 | /* |x| < 0x1p12 */ |
23 | return logf(2*x - 1/(x+sqrtf(x*x-1))); |
24 | /* x >= 0x1p12 */ |
25 | return logf(x) + 0.693147180559945309417232121458176568f; |
26 | } |
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