Last change
on this file was 337, checked in by coas-nagasima, 6 years ago |
ASP3版ECNLを追加
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Property svn:eol-style
set to
native
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Property svn:mime-type
set to
text/x-csrc;charset=UTF-8
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File size:
577 bytes
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[337] | 1 | #include "libm.h"
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| 2 |
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| 3 | /* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */
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| 4 | double atanh(double x)
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| 5 | {
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| 6 | union {double f; uint64_t i;} u = {.f = x};
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| 7 | unsigned e = u.i >> 52 & 0x7ff;
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| 8 | unsigned s = u.i >> 63;
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| 9 | double_t y;
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| 10 |
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| 11 | /* |x| */
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| 12 | u.i &= (uint64_t)-1/2;
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| 13 | y = u.f;
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| 14 |
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| 15 | if (e < 0x3ff - 1) {
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| 16 | if (e < 0x3ff - 32) {
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| 17 | /* handle underflow */
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| 18 | if (e == 0)
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| 19 | FORCE_EVAL((float)y);
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| 20 | } else {
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| 21 | /* |x| < 0.5, up to 1.7ulp error */
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| 22 | y = 0.5*log1p(2*y + 2*y*y/(1-y));
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| 23 | }
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| 24 | } else {
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| 25 | /* avoid overflow */
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| 26 | y = 0.5*log1p(2*(y/(1-y)));
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| 27 | }
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| 28 | return s ? -y : y;
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| 29 | }
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