Last change
on this file since 403 was 337, checked in by coas-nagasima, 6 years ago |
ASP3版ECNLを追加
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Property svn:eol-style
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native
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Property svn:mime-type
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text/x-csrc;charset=UTF-8
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File size:
577 bytes
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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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