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Use Kahan's formula in cacosh

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This commit is contained in:
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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6
math/s_cacoshl.c
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@ -65,6 +65,12 @@ __cacoshl (__complex__ long double x)
__real__ res = 0.0;
__imag__ res = __copysignl (M_PI_2l, __imag__ x);
}
/* The factor 16 is just a guess. */
else if (16.0L * fabsl (__imag__ x) < fabsl (__real__ x))
/* Kahan's formula which avoid cancellation through subtraction in
some cases. */
res = 2.0L * __clogl (__csqrtl ((x + 1.0L) / 2.0L)
+ __csqrtl ((x - 1.0L) / 2.0L));
else
{
__complex__ long double y;