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1 /* Compute a product of X, X+1, ..., with an error estimate.
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2 Copyright (C) 2013-2018 Free Software Foundation, Inc.
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3 This file is part of the GNU C Library.
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4
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5 The GNU C Library is free software; you can redistribute it and/or
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6 modify it under the terms of the GNU Lesser General Public
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7 License as published by the Free Software Foundation; either
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8 version 2.1 of the License, or (at your option) any later version.
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9
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10 The GNU C Library is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 Lesser General Public License for more details.
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14
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15 You should have received a copy of the GNU Lesser General Public
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16 License along with the GNU C Library; if not, see
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17 <http://www.gnu.org/licenses/>. */
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18
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19 #include "quadmath-imp.h"
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20
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21 /* Compute the product of X + X_EPS, X + X_EPS + 1, ..., X + X_EPS + N
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22 - 1, in the form R * (1 + *EPS) where the return value R is an
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23 approximation to the product and *EPS is set to indicate the
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24 approximate error in the return value. X is such that all the
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25 values X + 1, ..., X + N - 1 are exactly representable, and X_EPS /
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26 X is small enough that factors quadratic in it can be
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27 neglected. */
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28
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29 __float128
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30 __quadmath_gamma_productq (__float128 x, __float128 x_eps, int n, __float128 *eps)
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31 {
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32 SET_RESTORE_ROUNDF128 (FE_TONEAREST);
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33 __float128 ret = x;
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34 *eps = x_eps / x;
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35 for (int i = 1; i < n; i++)
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36 {
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37 *eps += x_eps / (x + i);
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38 __float128 lo;
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39 mul_splitq (&ret, &lo, ret, x + i);
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40 *eps += lo / ret;
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41 }
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42 return ret;
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43 }
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