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      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 }
     44