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authorUlrich Drepper <drepper@gmail.com>2011-12-21 22:08:12 -0500
committerUlrich Drepper <drepper@gmail.com>2011-12-21 22:08:12 -0500
commite3a851a21bb69a4b18065dd859a724cfd984d8b3 (patch)
tree684234898c2ac6b0d426658503315e9e4855a9d5 /math/s_cacoshl.c
parentb27e24b8746b20d9ded426f202b79c3b7aeb953e (diff)
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Use Kahan's formula in cacosh
Diffstat (limited to 'math/s_cacoshl.c')
-rw-r--r--math/s_cacoshl.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/math/s_cacoshl.c b/math/s_cacoshl.c
index b90b196..84c2715 100644
--- a/math/s_cacoshl.c
+++ b/math/s_cacoshl.c
@@ -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;