1 /* mpn_dcpi1_bdiv_q -- divide-and-conquer Hensel division with precomputed 2 inverse, returning quotient. 3 4 Contributed to the GNU project by Niels M�ller and Torbjorn Granlund. 5 6 THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES. IT IS ONLY 7 SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST 8 GUARANTEED THAT THEY WILL CHANGE OR DISAPPEAR IN A FUTURE GMP RELEASE. 9 10 Copyright 2006, 2007, 2009, 2010, 2011 Free Software Foundation, Inc. 11 12 This file is part of the GNU MP Library. 13 14 The GNU MP Library is free software; you can redistribute it and/or modify 15 it under the terms of the GNU Lesser General Public License as published by 16 the Free Software Foundation; either version 3 of the License, or (at your 17 option) any later version. 18 19 The GNU MP Library is distributed in the hope that it will be useful, but 20 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 21 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 22 License for more details. 23 24 You should have received a copy of the GNU Lesser General Public License 25 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 26 27 #include "gmp.h" 28 #include "gmp-impl.h" 29 30 31 mp_size_t 32 mpn_dcpi1_bdiv_q_n_itch (mp_size_t n) 33 { 34 /* NOTE: Depends on mullo_n interface */ 35 return n; 36 } 37 38 /* Computes Q = N / D mod B^n, destroys N. 39 40 N = {np,n} 41 D = {dp,n} 42 */ 43 44 void 45 mpn_dcpi1_bdiv_q_n (mp_ptr qp, 46 mp_ptr np, mp_srcptr dp, mp_size_t n, 47 mp_limb_t dinv, mp_ptr tp) 48 { 49 while (ABOVE_THRESHOLD (n, DC_BDIV_Q_THRESHOLD)) 50 { 51 mp_size_t lo, hi; 52 mp_limb_t cy; 53 54 lo = n >> 1; /* floor(n/2) */ 55 hi = n - lo; /* ceil(n/2) */ 56 57 cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, lo, dinv, tp); 58 59 mpn_mullo_n (tp, qp, dp + hi, lo); 60 mpn_sub_n (np + hi, np + hi, tp, lo); 61 62 if (lo < hi) 63 { 64 cy += mpn_submul_1 (np + lo, qp, lo, dp[lo]); 65 np[n - 1] -= cy; 66 } 67 qp += lo; 68 np += lo; 69 n -= lo; 70 } 71 mpn_sbpi1_bdiv_q (qp, np, n, dp, n, dinv); 72 } 73 74 /* Computes Q = N / D mod B^nn, destroys N. 75 76 N = {np,nn} 77 D = {dp,dn} 78 */ 79 80 void 81 mpn_dcpi1_bdiv_q (mp_ptr qp, 82 mp_ptr np, mp_size_t nn, 83 mp_srcptr dp, mp_size_t dn, 84 mp_limb_t dinv) 85 { 86 mp_size_t qn; 87 mp_limb_t cy; 88 mp_ptr tp; 89 TMP_DECL; 90 91 TMP_MARK; 92 93 ASSERT (dn >= 2); 94 ASSERT (nn - dn >= 0); 95 ASSERT (dp[0] & 1); 96 97 tp = TMP_SALLOC_LIMBS (dn); 98 99 qn = nn; 100 101 if (qn > dn) 102 { 103 /* Reduce qn mod dn in a super-efficient manner. */ 104 do 105 qn -= dn; 106 while (qn > dn); 107 108 /* Perform the typically smaller block first. */ 109 if (BELOW_THRESHOLD (qn, DC_BDIV_QR_THRESHOLD)) 110 cy = mpn_sbpi1_bdiv_qr (qp, np, 2 * qn, dp, qn, dinv); 111 else 112 cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, qn, dinv, tp); 113 114 if (qn != dn) 115 { 116 if (qn > dn - qn) 117 mpn_mul (tp, qp, qn, dp + qn, dn - qn); 118 else 119 mpn_mul (tp, dp + qn, dn - qn, qp, qn); 120 mpn_incr_u (tp + qn, cy); 121 122 mpn_sub (np + qn, np + qn, nn - qn, tp, dn); 123 cy = 0; 124 } 125 126 np += qn; 127 qp += qn; 128 129 qn = nn - qn; 130 while (qn > dn) 131 { 132 mpn_sub_1 (np + dn, np + dn, qn - dn, cy); 133 cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, dn, dinv, tp); 134 qp += dn; 135 np += dn; 136 qn -= dn; 137 } 138 mpn_dcpi1_bdiv_q_n (qp, np, dp, dn, dinv, tp); 139 } 140 else 141 { 142 if (BELOW_THRESHOLD (qn, DC_BDIV_Q_THRESHOLD)) 143 mpn_sbpi1_bdiv_q (qp, np, qn, dp, qn, dinv); 144 else 145 mpn_dcpi1_bdiv_q_n (qp, np, dp, qn, dinv, tp); 146 } 147 148 TMP_FREE; 149 } 150