From d8cd06db62d92f86cc8cc3c0d6a489bd207bb834 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Wed, 8 May 2013 11:58:18 +0000 Subject: Improve tgamma accuracy (bugs 2546, 2560, 5159, 15426). --- sysdeps/ieee754/dbl-64/gamma_productf.c | 46 +++++++++++++++++++++++++++++++++ 1 file changed, 46 insertions(+) create mode 100644 sysdeps/ieee754/dbl-64/gamma_productf.c (limited to 'sysdeps/ieee754/dbl-64/gamma_productf.c') diff --git a/sysdeps/ieee754/dbl-64/gamma_productf.c b/sysdeps/ieee754/dbl-64/gamma_productf.c new file mode 100644 index 0000000000..46072f16ea --- /dev/null +++ b/sysdeps/ieee754/dbl-64/gamma_productf.c @@ -0,0 +1,46 @@ +/* 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 + . */ + +#include +#include +#include + +/* 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. */ + +float +__gamma_productf (float x, float x_eps, int n, float *eps) +{ + double x_full = (double) x + (double) x_eps; + double ret = x_full; + for (int i = 1; i < n; i++) + ret *= x_full + i; + +#if FLT_EVAL_METHOD != 0 + volatile +#endif + float fret = ret; + *eps = (ret - fret) / fret; + + return fret; +} -- cgit 1.4.1