1/* Compute a product of X, X+1, ..., with an error estimate.
2 Copyright (C) 2013-2017 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
18
19#include <math.h>
20#include <math_private.h>
21#include <mul_splitl.h>
22
23/* Compute the product of X + X_EPS, X + X_EPS + 1, ..., X + X_EPS + N
24 - 1, in the form R * (1 + *EPS) where the return value R is an
25 approximation to the product and *EPS is set to indicate the
26 approximate error in the return value. X is such that all the
27 values X + 1, ..., X + N - 1 are exactly representable, and X_EPS /
28 X is small enough that factors quadratic in it can be
29 neglected. */
30
31_Float128
32__gamma_productl (_Float128 x, _Float128 x_eps, int n, _Float128 *eps)
33{
34 SET_RESTORE_ROUNDL (FE_TONEAREST);
35 _Float128 ret = x;
36 *eps = x_eps / x;
37 for (int i = 1; i < n; i++)
38 {
39 *eps += x_eps / (x + i);
40 _Float128 lo;
41 mul_splitl (&ret, &lo, ret, x + i);
42 *eps += lo / ret;
43 }
44 return ret;
45}
46