35 lines
926 B
C
35 lines
926 B
C
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/*****************************************************************************/
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/*****************************************************************************/
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// atanhf from musl-0.9.15
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/*****************************************************************************/
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/*****************************************************************************/
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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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float atanhf(float x)
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{
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union {float f; uint32_t i;} u = {.f = x};
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unsigned s = u.i >> 31;
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float_t y;
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/* |x| */
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u.i &= 0x7fffffff;
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y = u.f;
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if (u.i < 0x3f800000 - (1<<23)) {
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if (u.i < 0x3f800000 - (32<<23)) {
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/* handle underflow */
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if (u.i < (1<<23))
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FORCE_EVAL((float)(y*y));
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} else {
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/* |x| < 0.5, up to 1.7ulp error */
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y = 0.5f*log1pf(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 = 0.5f*log1pf(2*(y/(1-y)));
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}
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return s ? -y : y;
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}
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