1 /* Compute a product of 1 + (T/X), 1 + (T/(X+1)), .... 2 Copyright (C) 2015-2018 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 1 + (T / (X + X_EPS)), 1 + (T / (X + X_EPS + 22 1)), ..., 1 + (T / (X + X_EPS + N - 1)), minus 1. X is such that 23 all the values X + 1, ..., X + N - 1 are exactly representable, and 24 X_EPS / X is small enough that factors quadratic in it can be 25 neglected. */ 26 27 __float128 28 __quadmath_lgamma_productq (__float128 t, __float128 x, __float128 x_eps, int n) 29 { 30 __float128 ret = 0, ret_eps = 0; 31 for (int i = 0; i < n; i++) 32 { 33 __float128 xi = x + i; 34 __float128 quot = t / xi; 35 __float128 mhi, mlo; 36 mul_splitq (&mhi, &mlo, quot, xi); 37 __float128 quot_lo = (t - mhi - mlo) / xi - t * x_eps / (xi * xi); 38 /* We want (1 + RET + RET_EPS) * (1 + QUOT + QUOT_LO) - 1. */ 39 __float128 rhi, rlo; 40 mul_splitq (&rhi, &rlo, ret, quot); 41 __float128 rpq = ret + quot; 42 __float128 rpq_eps = (ret - rpq) + quot; 43 __float128 nret = rpq + rhi; 44 __float128 nret_eps = (rpq - nret) + rhi; 45 ret_eps += (rpq_eps + nret_eps + rlo + ret_eps * quot 46 + quot_lo + quot_lo * (ret + ret_eps)); 47 ret = nret; 48 } 49 return ret + ret_eps; 50 } 51
Indexes created Sun Mar 01 05:31:48 UTC 2026