| /* Compute a product of 1 + (T/X), 1 + (T/(X+1)), .... |
| Copyright (C) 2015-2018 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 <math.h> |
| #include <math_private.h> |
| #include <float.h> |
| |
| /* Compute the product of 1 + (T / (X + X_EPS)), 1 + (T / (X + X_EPS + |
| 1)), ..., 1 + (T / (X + X_EPS + N - 1)), minus 1. 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. */ |
| |
| double |
| __lgamma_product (double t, double x, double x_eps, int n) |
| { |
| long double x_full = (long double) x + (long double) x_eps; |
| long double ret = 0; |
| for (int i = 0; i < n; i++) |
| ret += (t / (x_full + i)) * (1 + ret); |
| return ret; |
| } |
