text: /* Compute a product of X, X+1, ..., with an error estimate.
     Copyright (C) 2013-2020 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-narrow-eval.h>
  #include <math_private.h>
  #include <float.h>
  
  /* Compute the product of X + X_EPS, X + X_EPS + 1, ..., X + X_EPS + N
     - 1, in the form R * (1 + *EPS) where the return value R is an
     approximation to the product and *EPS is set to indicate the
     approximate error in the return value.  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.  */
  
  float
  __gamma_productf (float x, float x_eps, int n, float *eps)
  {
    double x_full = (double) x + (double) x_eps;
    double ret = x_full;
    for (int i = 1; i < n; i++)
      ret *= x_full + i;
  
    float fret = math_narrow_eval ((float) ret);
    *eps = (ret - fret) / fret;
  
    return fret;
  }
  