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  }