1 /* mpn_sbpi1_bdiv_qr -- schoolbook Hensel division with precomputed inverse, 2 returning quotient and remainder. 3 4 Contributed to the GNU project by Niels M�ller. 5 6 THE FUNCTIONS IN THIS FILE ARE INTERNAL FUNCTIONS WITH MUTABLE INTERFACES. 7 IT IS ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS 8 ALMOST GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GMP RELEASE. 9 10 Copyright 2006, 2009 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 /* Computes a binary quotient of size qn = nn - dn. 32 Output: 33 34 Q = N * D^{-1} mod B^qn, 35 36 R = (N - Q * D) * B^(-qn) 37 38 Stores the dn least significant limbs of R at {np + nn - dn, dn}, 39 and returns the borrow from the subtraction N - Q*D. 40 41 D must be odd. dinv is (-D)^-1 mod B. */ 42 43 mp_limb_t 44 mpn_sbpi1_bdiv_qr (mp_ptr qp, 45 mp_ptr np, mp_size_t nn, 46 mp_srcptr dp, mp_size_t dn, mp_limb_t dinv) 47 { 48 mp_size_t qn; 49 mp_size_t i; 50 mp_limb_t rh; 51 mp_limb_t ql; 52 53 ASSERT (dn > 0); 54 ASSERT (nn > dn); 55 ASSERT ((dp[0] & 1) != 0); 56 57 qn = nn - dn; 58 59 rh = 0; 60 61 /* To complete the negation, this value is added to q. */ 62 ql = 1; 63 while (qn > dn) 64 { 65 for (i = 0; i < dn; i++) 66 { 67 mp_limb_t q; 68 69 q = dinv * np[i]; 70 qp[i] = ~q; 71 72 np[i] = mpn_addmul_1 (np + i, dp, dn, q); 73 } 74 rh += mpn_add (np + dn, np + dn, qn, np, dn); 75 ql = mpn_add_1 (qp, qp, dn, ql); 76 77 qp += dn; qn -= dn; 78 np += dn; nn -= dn; 79 } 80 81 for (i = 0; i < qn; i++) 82 { 83 mp_limb_t q; 84 85 q = dinv * np[i]; 86 qp[i] = ~q; 87 88 np[i] = mpn_addmul_1 (np + i, dp, dn, q); 89 } 90 91 rh += mpn_add_n (np + dn, np + dn, np, qn); 92 ql = mpn_add_1 (qp, qp, qn, ql); 93 94 if (UNLIKELY (ql > 0)) 95 { 96 /* q == 0 */ 97 ASSERT (rh == 0); 98 return 0; 99 } 100 else 101 { 102 mp_limb_t cy; 103 104 cy = mpn_sub_n (np + qn, np + qn, dp, dn); 105 ASSERT (cy >= rh); 106 return cy - rh; 107 } 108 } 109