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Use Kahan's formula in cacosh

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Ulrich Drepper
2011-12-21 22:08:12 -05:00
parent b27e24b874
commit e3a851a21b
4 changed files with 24 additions and 0 deletions
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math/s_cacosh.c
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@ -65,6 +65,11 @@ __cacosh (__complex__ double x)
__real__ res = 0.0;
__imag__ res = __copysign (M_PI_2, __imag__ x);
}
/* The factor 16 is just a guess. */
else if (16.0 * fabs (__imag__ x) < fabs (__real__ x))
/* Kahan's formula which avoid cancellation through subtraction in
some cases. */
res = 2.0 * __clog (__csqrt ((x + 1.0) / 2.0) + __csqrt ((x - 1.0) / 2.0));
else
{
__complex__ double y;