source:
asp3_tinet_ecnl_rx/trunk/musl-1.1.18/src/math/atanhf.c
Last change on this file was 337, checked in by , 6 years ago | |
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File size: 578 bytes |
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1 | #include "libm.h" |
2 | |
3 | /* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */ |
4 | float atanhf(float x) |
5 | { |
6 | union {float f; uint32_t i;} u = {.f = x}; |
7 | unsigned s = u.i >> 31; |
8 | float_t y; |
9 | |
10 | /* |x| */ |
11 | u.i &= 0x7fffffff; |
12 | y = u.f; |
13 | |
14 | if (u.i < 0x3f800000 - (1<<23)) { |
15 | if (u.i < 0x3f800000 - (32<<23)) { |
16 | /* handle underflow */ |
17 | if (u.i < (1<<23)) |
18 | FORCE_EVAL((float)(y*y)); |
19 | } else { |
20 | /* |x| < 0.5, up to 1.7ulp error */ |
21 | y = 0.5f*log1pf(2*y + 2*y*y/(1-y)); |
22 | } |
23 | } else { |
24 | /* avoid overflow */ |
25 | y = 0.5f*log1pf(2*(y/(1-y))); |
26 | } |
27 | return s ? -y : y; |
28 | } |
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