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Diffstat (limited to 'libquadmath/math/tgammaq_product.c')
-rw-r--r-- | libquadmath/math/tgammaq_product.c | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/libquadmath/math/tgammaq_product.c b/libquadmath/math/tgammaq_product.c new file mode 100644 index 00000000000..8f9e56dbac2 --- /dev/null +++ b/libquadmath/math/tgammaq_product.c @@ -0,0 +1,43 @@ +/* Compute a product of X, X+1, ..., with an error estimate. + Copyright (C) 2013-2018 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 "quadmath-imp.h" + +/* 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. */ + +__float128 +__quadmath_gamma_productq (__float128 x, __float128 x_eps, int n, __float128 *eps) +{ + SET_RESTORE_ROUNDF128 (FE_TONEAREST); + __float128 ret = x; + *eps = x_eps / x; + for (int i = 1; i < n; i++) + { + *eps += x_eps / (x + i); + __float128 lo; + mul_splitq (&ret, &lo, ret, x + i); + *eps += lo / ret; + } + return ret; +} |