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 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 32 mp_size_t 33 mpn_dcpi1_bdiv_q_n_itch (mp_size_t n) 34 { 35 /* NOTE: Depends on mullo_n interface */ 36 return n; 37 } 38 39 /* Computes Q = N / D mod B^n, destroys N. 40 41 N = {np,n} 42 D = {dp,n} 43 */ 44 45 void 46 mpn_dcpi1_bdiv_q_n (mp_ptr qp, 47 mp_ptr np, mp_srcptr dp, mp_size_t n, 48 mp_limb_t dinv, mp_ptr tp) 49 { 50 while (ABOVE_THRESHOLD (n, DC_BDIV_Q_THRESHOLD)) 51 { 52 mp_size_t lo, hi; 53 mp_limb_t cy; 54 55 lo = n >> 1; /* floor(n/2) */ 56 hi = n - lo; /* ceil(n/2) */ 57 58 cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, lo, dinv, tp); 59 60 mpn_mullo_n (tp, qp, dp + hi, lo); 61 mpn_sub_n (np + hi, np + hi, tp, lo); 62 63 if (lo < hi) 64 { 65 cy += mpn_submul_1 (np + lo, qp, lo, dp[lo]); 66 np[n - 1] -= cy; 67 } 68 qp += lo; 69 np += lo; 70 n -= lo; 71 } 72 mpn_sbpi1_bdiv_q (qp, np, n, dp, n, dinv); 73 } 74 75 /* Computes Q = N / D mod B^nn, destroys N. 76 77 N = {np,nn} 78 D = {dp,dn} 79 */ 80 81 void 82 mpn_dcpi1_bdiv_q (mp_ptr qp, 83 mp_ptr np, mp_size_t nn, 84 mp_srcptr dp, mp_size_t dn, 85 mp_limb_t dinv) 86 { 87 mp_size_t qn; 88 mp_limb_t cy; 89 mp_ptr tp; 90 TMP_DECL; 91 92 TMP_MARK; 93 94 ASSERT (dn >= 2); 95 ASSERT (nn - dn >= 0); 96 ASSERT (dp[0] & 1); 97 98 tp = TMP_SALLOC_LIMBS (dn); 99 100 qn = nn; 101 102 if (qn > dn) 103 { 104 /* Reduce qn mod dn in a super-efficient manner. */ 105 do 106 qn -= dn; 107 while (qn > dn); 108 109 /* Perform the typically smaller block first. */ 110 if (BELOW_THRESHOLD (qn, DC_BDIV_QR_THRESHOLD)) 111 cy = mpn_sbpi1_bdiv_qr (qp, np, 2 * qn, dp, qn, dinv); 112 else 113 cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, qn, dinv, tp); 114 115 if (qn != dn) 116 { 117 if (qn > dn - qn) 118 mpn_mul (tp, qp, qn, dp + qn, dn - qn); 119 else 120 mpn_mul (tp, dp + qn, dn - qn, qp, qn); 121 mpn_incr_u (tp + qn, cy); 122 123 mpn_sub (np + qn, np + qn, nn - qn, tp, dn); 124 cy = 0; 125 } 126 127 np += qn; 128 qp += qn; 129 130 qn = nn - qn; 131 while (qn > dn) 132 { 133 mpn_sub_1 (np + dn, np + dn, qn, cy); 134 cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, dn, dinv, tp); 135 qp += dn; 136 np += dn; 137 qn -= dn; 138 } 139 mpn_dcpi1_bdiv_q_n (qp, np, dp, dn, dinv, tp); 140 } 141 else 142 { 143 if (BELOW_THRESHOLD (qn, DC_BDIV_Q_THRESHOLD)) 144 mpn_sbpi1_bdiv_q (qp, np, qn, dp, qn, dinv); 145 else 146 mpn_dcpi1_bdiv_q_n (qp, np, dp, qn, dinv, tp); 147 } 148 149 TMP_FREE; 150 } 151