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-rw-r--r--math/s_cacoshf.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/math/s_cacoshf.c b/math/s_cacoshf.c
index aa4696f10b..fe046929e8 100644
--- a/math/s_cacoshf.c
+++ b/math/s_cacoshf.c
@@ -65,6 +65,12 @@ __cacoshf (__complex__ float x)
__real__ res = 0.0;
__imag__ res = __copysignf (M_PI_2, __imag__ x);
}
+ /* The factor 16 is just a guess. */
+ else if (16.0 * fabsf (__imag__ x) < fabsf (__real__ x))
+ /* Kahan's formula which avoid cancellation through subtraction in
+ some cases. */
+ res = 2.0 * __clogf (__csqrtf ((x + 1.0) / 2.0)
+ + __csqrtf ((x - 1.0) / 2.0));
else
{
__complex__ float y;