blob: 73091a8281e09d11b42cc71cf9ad52874169a8e6 [file] [log] [blame]
 /* 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 . */ #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; }