text: /* Compute a product of 1 + (T/X), 1 + (T/(X+1)), ....
     Copyright (C) 2015-2020 Free Software Foundation, Inc.
     This file is part of the GNU C Library.
  
     The GNU C Library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Lesser General Public
     License as published by the Free Software Foundation; either
     version 2.1 of the License, or (at your option) any later version.
  
     The GNU C Library is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Lesser General Public License for more details.
  
     You should have received a copy of the GNU Lesser General Public
     License along with the GNU C Library; if not, see
     <https://www.gnu.org/licenses/>.  */
  
  #include <math.h>
  #include <math_private.h>
  #include <float.h>
  
  /* Compute the product of 1 + (T / (X + X_EPS)), 1 + (T / (X + X_EPS +
     1)), ..., 1 + (T / (X + X_EPS + N - 1)), minus 1.  X is such that
     all the values X + 1, ..., X + N - 1 are exactly representable, and
     X_EPS / X is small enough that factors quadratic in it can be
     neglected.  */
  
  double
  __lgamma_product (double t, double x, double x_eps, int n)
  {
    long double x_full = (long double) x + (long double) x_eps;
    long double ret = 0;
    for (int i = 0; i < n; i++)
      ret += (t / (x_full + i)) * (1 + ret);
    return ret;
  }
  