1 /* mpn_redc_n. Set cp[] <- up[]/R^n mod mp[]. Clobber up[]. 2 mp[] is n limbs; up[] is 2n limbs, the inverse ip[] is n limbs. 3 4 THIS IS AN INTERNAL FUNCTION WITH A MUTABLE INTERFACE. IT IS ONLY 5 SAFE TO REACH THIS FUNCTION THROUGH DOCUMENTED INTERFACES. 6 7 Copyright (C) 2009 Free Software Foundation, Inc. 8 9 This file is part of the GNU MP Library. 10 11 The GNU MP Library is free software; you can redistribute it and/or modify 12 it under the terms of the GNU Lesser General Public License as published by 13 the Free Software Foundation; either version 3 of the License, or (at your 14 option) any later version. 15 16 The GNU MP Library is distributed in the hope that it will be useful, but 17 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 18 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 19 License for more details. 20 21 You should have received a copy of the GNU Lesser General Public License 22 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 23 24 #include "gmp.h" 25 #include "gmp-impl.h" 26 27 /* 28 TODO 29 30 * We assume mpn_mulmod_bnm1 is always faster than plain mpn_mul_n (or a 31 future mpn_mulhi) for the range we will be called. Follow up that 32 assumption. 33 34 * Decrease scratch usage. 35 */ 36 37 void 38 mpn_redc_n (mp_ptr rp, mp_ptr up, mp_srcptr mp, mp_size_t n, mp_srcptr ip) 39 { 40 mp_ptr xp, yp, scratch; 41 mp_limb_t cy; 42 mp_size_t rn; 43 TMP_DECL; 44 TMP_MARK; 45 46 rn = mpn_mulmod_bnm1_next_size (n); 47 48 scratch = TMP_ALLOC_LIMBS (n + rn + mpn_mulmod_bnm1_itch (rn, n, n)); 49 50 xp = scratch; 51 mpn_mullo_n (xp, up, ip, n); 52 53 yp = scratch + n; 54 mpn_mulmod_bnm1 (yp, rn, xp, n, mp, n, scratch + n + rn); 55 56 ASSERT_ALWAYS (2 * n > rn); /* could handle this */ 57 58 cy = mpn_sub_n (yp + rn, yp, up, 2*n - rn); /* undo wrap around */ 59 MPN_DECR_U (yp + 2*n - rn, rn, cy); 60 61 cy = mpn_sub_n (rp, up + n, yp + n, n); 62 if (cy != 0) 63 mpn_add_n (rp, rp, mp, n); 64 65 TMP_FREE; 66 } 67