Last change
on this file since 446 was 444, checked in by coas-nagasima, 4 years ago |
muslのソースコードを追加
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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:
996 bytes
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Rev | Line | |
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[444] | 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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