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author | Joseph Myers <joseph@codesourcery.com> | 2013-05-08 11:58:18 +0000 |
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committer | Joseph Myers <joseph@codesourcery.com> | 2013-05-08 11:58:18 +0000 |
commit | d8cd06db62d92f86cc8cc3c0d6a489bd207bb834 (patch) | |
tree | 3906235135ce8e0b4ea11d5dadc076699be07738 /sysdeps/ieee754/ldbl-96/gamma_productl.c | |
parent | bb7cf681e90d5aa2d867aeff4948ac605447de7d (diff) | |
download | glibc-d8cd06db62d92f86cc8cc3c0d6a489bd207bb834.tar.gz |
Improve tgamma accuracy (bugs 2546, 2560, 5159, 15426).
Diffstat (limited to 'sysdeps/ieee754/ldbl-96/gamma_productl.c')
-rw-r--r-- | sysdeps/ieee754/ldbl-96/gamma_productl.c | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/sysdeps/ieee754/ldbl-96/gamma_productl.c b/sysdeps/ieee754/ldbl-96/gamma_productl.c new file mode 100644 index 0000000000..157dbab9fb --- /dev/null +++ b/sysdeps/ieee754/ldbl-96/gamma_productl.c @@ -0,0 +1,75 @@ +/* Compute a product of X, X+1, ..., with an error estimate. + Copyright (C) 2013 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <http://www.gnu.org/licenses/>. */ + +#include <math.h> +#include <math_private.h> +#include <float.h> + +/* Calculate X * Y exactly and store the result in *HI + *LO. It is + given that the values are small enough that no overflow occurs and + large enough (or zero) that no underflow occurs. */ + +static inline void +mul_split (long double *hi, long double *lo, long double x, long double y) +{ +#ifdef __FP_FAST_FMAL + /* Fast built-in fused multiply-add. */ + *hi = x * y; + *lo = __builtin_fmal (x, y, -*hi); +#elif defined FP_FAST_FMAL + /* Fast library fused multiply-add, compiler before GCC 4.6. */ + *hi = x * y; + *lo = __fmal (x, y, -*hi); +#else + /* Apply Dekker's algorithm. */ + *hi = x * y; +# define C ((1LL << (LDBL_MANT_DIG + 1) / 2) + 1) + long double x1 = x * C; + long double y1 = y * C; +# undef C + x1 = (x - x1) + x1; + y1 = (y - y1) + y1; + long double x2 = x - x1; + long double y2 = y - y1; + *lo = (((x1 * y1 - *hi) + x1 * y2) + x2 * y1) + x2 * y2; +#endif +} + +/* Compute the product of X + X_EPS, X + X_EPS + 1, ..., X + X_EPS + N + - 1, in the form R * (1 + *EPS) where the return value R is an + approximation to the product and *EPS is set to indicate the + approximate error in the return value. X is such that all the + values X + 1, ..., X + N - 1 are exactly representable, and X_EPS / + X is small enough that factors quadratic in it can be + neglected. */ + +long double +__gamma_productl (long double x, long double x_eps, int n, long double *eps) +{ + SET_RESTORE_ROUNDL (FE_TONEAREST); + long double ret = x; + *eps = x_eps / x; + for (int i = 1; i < n; i++) + { + *eps += x_eps / (x + i); + long double lo; + mul_split (&ret, &lo, ret, x + i); + *eps += lo / ret; + } + return ret; +} |