145
|
1 /* Compute a product of X, X+1, ..., with an error estimate.
|
|
2 Copyright (C) 2013-2018 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 "quadmath-imp.h"
|
|
20
|
|
21 /* Compute the product of X + X_EPS, X + X_EPS + 1, ..., X + X_EPS + N
|
|
22 - 1, in the form R * (1 + *EPS) where the return value R is an
|
|
23 approximation to the product and *EPS is set to indicate the
|
|
24 approximate error in the return value. X is such that all the
|
|
25 values X + 1, ..., X + N - 1 are exactly representable, and X_EPS /
|
|
26 X is small enough that factors quadratic in it can be
|
|
27 neglected. */
|
|
28
|
|
29 __float128
|
|
30 __quadmath_gamma_productq (__float128 x, __float128 x_eps, int n, __float128 *eps)
|
|
31 {
|
|
32 SET_RESTORE_ROUNDF128 (FE_TONEAREST);
|
|
33 __float128 ret = x;
|
|
34 *eps = x_eps / x;
|
|
35 for (int i = 1; i < n; i++)
|
|
36 {
|
|
37 *eps += x_eps / (x + i);
|
|
38 __float128 lo;
|
|
39 mul_splitq (&ret, &lo, ret, x + i);
|
|
40 *eps += lo / ret;
|
|
41 }
|
|
42 return ret;
|
|
43 }
|