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| author | Ulrich Drepper <drepper@gmail.com> | 2011-12-21 22:08:12 -0500 |
|---|---|---|
| committer | Ulrich Drepper <drepper@gmail.com> | 2011-12-21 22:08:12 -0500 |
| commit | e3a851a21bb69a4b18065dd859a724cfd984d8b3 (patch) | |
| tree | 684234898c2ac6b0d426658503315e9e4855a9d5 /math/s_cacosh.c | |
| parent | b27e24b8746b20d9ded426f202b79c3b7aeb953e (diff) | |
| download | glibc-e3a851a21bb69a4b18065dd859a724cfd984d8b3.zip glibc-e3a851a21bb69a4b18065dd859a724cfd984d8b3.tar.gz glibc-e3a851a21bb69a4b18065dd859a724cfd984d8b3.tar.bz2 | |
Use Kahan's formula in cacosh
Diffstat (limited to 'math/s_cacosh.c')
| -rw-r--r-- | math/s_cacosh.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/math/s_cacosh.c b/math/s_cacosh.c index df5ce69..cb01ca8 100644 --- a/math/s_cacosh.c +++ b/math/s_cacosh.c @@ -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; |