Last change
on this file since 351 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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Property svn:mime-type
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File size:
996 bytes
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1 | #include "libm.h"
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2 |
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3 | /* tanh(x) = (exp(x) - exp(-x))/(exp(x) + exp(-x))
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4 | * = (exp(2*x) - 1)/(exp(2*x) - 1 + 2)
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5 | * = (1 - exp(-2*x))/(exp(-2*x) - 1 + 2)
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6 | */
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7 | double tanh(double x)
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8 | {
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9 | union {double f; uint64_t i;} u = {.f = x};
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10 | uint32_t w;
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11 | int sign;
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12 | double_t t;
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13 |
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14 | /* x = |x| */
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15 | sign = u.i >> 63;
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16 | u.i &= (uint64_t)-1/2;
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17 | x = u.f;
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18 | w = u.i >> 32;
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19 |
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20 | if (w > 0x3fe193ea) {
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21 | /* |x| > log(3)/2 ~= 0.5493 or nan */
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22 | if (w > 0x40340000) {
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23 | /* |x| > 20 or nan */
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24 | /* note: this branch avoids raising overflow */
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25 | t = 1 - 0/x;
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26 | } else {
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27 | t = expm1(2*x);
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28 | t = 1 - 2/(t+2);
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29 | }
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30 | } else if (w > 0x3fd058ae) {
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31 | /* |x| > log(5/3)/2 ~= 0.2554 */
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32 | t = expm1(2*x);
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33 | t = t/(t+2);
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34 | } else if (w >= 0x00100000) {
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35 | /* |x| >= 0x1p-1022, up to 2ulp error in [0.1,0.2554] */
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36 | t = expm1(-2*x);
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37 | t = -t/(t+2);
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38 | } else {
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39 | /* |x| is subnormal */
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40 | /* note: the branch above would not raise underflow in [0x1p-1023,0x1p-1022) */
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41 | FORCE_EVAL((float)x);
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42 | t = x;
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43 | }
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44 | return sign ? -t : t;
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45 | }
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