36 lines
757 B
C
36 lines
757 B
C
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#include "libc/math/libm.h"
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#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
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long double atanhl(long double x)
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{
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return atanh(x);
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}
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#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
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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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long double atanhl(long double x)
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{
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union ldshape u = {x};
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unsigned e = u.i.se & 0x7fff;
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unsigned s = u.i.se >> 15;
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/* |x| */
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u.i.se = e;
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x = u.f;
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if (e < 0x3ff - 1) {
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if (e < 0x3ff - LDBL_MANT_DIG/2) {
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/* handle underflow */
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if (e == 0)
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FORCE_EVAL((float)x);
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} else {
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/* |x| < 0.5, up to 1.7ulp error */
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x = 0.5*log1pl(2*x + 2*x*x/(1-x));
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}
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} else {
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/* avoid overflow */
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x = 0.5*log1pl(2*(x/(1-x)));
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}
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return s ? -x : x;
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}
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#endif
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