kopia lustrzana https://github.com/micropython/micropython
30 wiersze
577 B
C
30 wiersze
577 B
C
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#include "libm.h"
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/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */
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double atanh(double x)
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{
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union {double f; uint64_t i;} u = {.f = x};
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unsigned e = u.i >> 52 & 0x7ff;
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unsigned s = u.i >> 63;
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double_t y;
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/* |x| */
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u.i &= (uint64_t)-1/2;
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y = u.f;
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if (e < 0x3ff - 1) {
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if (e < 0x3ff - 32) {
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/* handle underflow */
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if (e == 0)
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FORCE_EVAL((float)y);
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} else {
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/* |x| < 0.5, up to 1.7ulp error */
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y = 0.5*log1p(2*y + 2*y*y/(1-y));
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}
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} else {
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/* avoid overflow */
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y = 0.5*log1p(2*(y/(1-y)));
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}
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return s ? -y : y;
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}
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