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| author | Ulrich Drepper <drepper@gmail.com> | 2011-12-21 22:08:12 -0500 |
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| committer | Ulrich Drepper <drepper@gmail.com> | 2011-12-21 22:08:12 -0500 |
| commit | e3a851a21bb69a4b18065dd859a724cfd984d8b3 (patch) | |
| tree | 684234898c2ac6b0d426658503315e9e4855a9d5 | |
| parent | b27e24b8746b20d9ded426f202b79c3b7aeb953e (diff) | |
| download | glibc-e3a851a21bb69a4b18065dd859a724cfd984d8b3.tar.gz glibc-e3a851a21bb69a4b18065dd859a724cfd984d8b3.tar.xz glibc-e3a851a21bb69a4b18065dd859a724cfd984d8b3.zip | |
Use Kahan's formula in cacosh
| -rw-r--r-- | ChangeLog | 7 | ||||
| -rw-r--r-- | math/s_cacosh.c | 5 | ||||
| -rw-r--r-- | math/s_cacoshf.c | 6 | ||||
| -rw-r--r-- | math/s_cacoshl.c | 6 |
4 files changed, 24 insertions, 0 deletions
diff --git a/ChangeLog b/ChangeLog index 1ccc3ddab0..4d2b1fcc98 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,10 @@ +2011-12-21 Ulrich Drepper <drepper@gmail.com> + + * math/s_cacosh.c: Use Kahan's formula if the subtraction could lead + to large cancellation. + * math/s_cacoshf.c: Likewise. + * math/s_cacoshl.c: Likewise. + 2011-11-18 Richard B. Kreckel <kreckel@ginac.de> [BZ #13305] diff --git a/math/s_cacosh.c b/math/s_cacosh.c index df5ce6945d..cb01ca87c5 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; 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; diff --git a/math/s_cacoshl.c b/math/s_cacoshl.c index b90b196959..84c2715d22 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; |