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d8cd06db | 1 | /* Compute a product of X, X+1, ..., with an error estimate. |
04277e02 | 2 | Copyright (C) 2013-2019 Free Software Foundation, Inc. |
d8cd06db JM |
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 | |
5a82c748 | 17 | <https://www.gnu.org/licenses/>. */ |
d8cd06db JM |
18 | |
19 | #include <math.h> | |
20 | #include <math_private.h> | |
70e2ba33 | 21 | #include <fenv_private.h> |
4482ff22 | 22 | #include <mul_splitl.h> |
d8cd06db JM |
23 | |
24 | /* Compute the product of X + X_EPS, X + X_EPS + 1, ..., X + X_EPS + N | |
25 | - 1, in the form R * (1 + *EPS) where the return value R is an | |
26 | approximation to the product and *EPS is set to indicate the | |
27 | approximate error in the return value. X is such that all the | |
28 | values X + 1, ..., X + N - 1 are exactly representable, and X_EPS / | |
29 | X is small enough that factors quadratic in it can be | |
30 | neglected. */ | |
31 | ||
15089e04 PM |
32 | _Float128 |
33 | __gamma_productl (_Float128 x, _Float128 x_eps, int n, _Float128 *eps) | |
d8cd06db JM |
34 | { |
35 | SET_RESTORE_ROUNDL (FE_TONEAREST); | |
15089e04 | 36 | _Float128 ret = x; |
d8cd06db JM |
37 | *eps = x_eps / x; |
38 | for (int i = 1; i < n; i++) | |
39 | { | |
40 | *eps += x_eps / (x + i); | |
15089e04 | 41 | _Float128 lo; |
4482ff22 | 42 | mul_splitl (&ret, &lo, ret, x + i); |
d8cd06db JM |
43 | *eps += lo / ret; |
44 | } | |
45 | return ret; | |
46 | } |