29 lines
697 B
C
29 lines
697 B
C
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#include "libm.h"
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/* asinh(x) = sign(x)*log(|x|+sqrt(x*x+1)) ~= x - x^3/6 + o(x^5) */
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double asinh(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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/* |x| */
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u.i &= (uint64_t)-1/2;
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x = u.f;
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if (e >= 0x3ff + 26) {
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/* |x| >= 0x1p26 or inf or nan */
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x = log(x) + 0.693147180559945309417232121458176568;
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} else if (e >= 0x3ff + 1) {
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/* |x| >= 2 */
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x = log(2*x + 1/(sqrt(x*x+1)+x));
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} else if (e >= 0x3ff - 26) {
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/* |x| >= 0x1p-26, up to 1.6ulp error in [0.125,0.5] */
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x = log1p(x + x*x/(sqrt(x*x+1)+1));
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} else {
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/* |x| < 0x1p-26, raise inexact if x != 0 */
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FORCE_EVAL(x + 0x1p120f);
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}
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return s ? -x : x;
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}
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