| /* Compute a product of 1 + (T/X), 1 + (T/(X+1)), .... |

| Copyright (C) 2015-2018 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 |

| <http://www.gnu.org/licenses/>. */ |

| |

| #include "quadmath-imp.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. */ |

| |

| __float128 |

| __quadmath_lgamma_productq (__float128 t, __float128 x, __float128 x_eps, int n) |

| { |

| __float128 ret = 0, ret_eps = 0; |

| for (int i = 0; i < n; i++) |

| { |

| __float128 xi = x + i; |

| __float128 quot = t / xi; |

| __float128 mhi, mlo; |

| mul_splitq (&mhi, &mlo, quot, xi); |

| __float128 quot_lo = (t - mhi - mlo) / xi - t * x_eps / (xi * xi); |

| /* We want (1 + RET + RET_EPS) * (1 + QUOT + QUOT_LO) - 1. */ |

| __float128 rhi, rlo; |

| mul_splitq (&rhi, &rlo, ret, quot); |

| __float128 rpq = ret + quot; |

| __float128 rpq_eps = (ret - rpq) + quot; |

| __float128 nret = rpq + rhi; |

| __float128 nret_eps = (rpq - nret) + rhi; |

| ret_eps += (rpq_eps + nret_eps + rlo + ret_eps * quot |

| + quot_lo + quot_lo * (ret + ret_eps)); |

| ret = nret; |

| } |

| return ret + ret_eps; |

| } |