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Justine Tunney 2020-06-15 07:18:57 -07:00
commit c91b3c5006
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35
libc/math/atanhl.c Normal file
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#include "libc/math/libm.h"
#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
long double atanhl(long double x)
{
return atanh(x);
}
#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */
long double atanhl(long double x)
{
union ldshape u = {x};
unsigned e = u.i.se & 0x7fff;
unsigned s = u.i.se >> 15;
/* |x| */
u.i.se = e;
x = u.f;
if (e < 0x3ff - 1) {
if (e < 0x3ff - LDBL_MANT_DIG/2) {
/* handle underflow */
if (e == 0)
FORCE_EVAL((float)x);
} else {
/* |x| < 0.5, up to 1.7ulp error */
x = 0.5*log1pl(2*x + 2*x*x/(1-x));
}
} else {
/* avoid overflow */
x = 0.5*log1pl(2*(x/(1-x)));
}
return s ? -x : x;
}
#endif