1 /* mpn_dc_divrem_n and auxilliary routines.
3 THE FUNCTIONS IN THIS FILE ARE INTERNAL FUNCTIONS WITH MUTABLE
4 INTERFACES. IT IS ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.
5 IN FACT, IT IS ALMOST GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A
9 Copyright 2000, 2001, 2002, 2004, 2005 Free Software Foundation, Inc.
10 Contributed by Paul Zimmermann.
12 This file is part of the GNU MP Library.
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.
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.
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/. */
31 [1] Fast Recursive Division, by Christoph Burnikel and Joachim Ziegler,
32 Technical report MPI-I-98-1-022, october 1998.
33 http://www.mpi-sb.mpg.de/~ziegler/TechRep.ps.gz
36 static mp_limb_t mpn_dc_div_3_by_2
37 __GMP_PROTO ((mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n, mp_ptr scratch));
38 static mp_limb_t mpn_dc_div_2_by_1
39 __GMP_PROTO ((mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n, mp_ptr scratch));
41 /* mpn_dc_divrem_n - Implements algorithm of page 8 in [1]: divides (np,2n)
42 by (dp,n) and puts the quotient in (qp,n), the remainder in (np,n).
43 Returns most significant limb of the quotient, which is 0 or 1.
44 Requires that the most significant bit of the divisor is set. */
47 mpn_dc_divrem_n (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n)
54 scratch = TMP_ALLOC_LIMBS (n);
55 ret = mpn_dc_div_2_by_1 (qp, np, dp, n, scratch);
62 mpn_dc_div_2_by_1 (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n, mp_ptr scratch)
70 qhl = mpn_dc_div_3_by_2 (qp1 + n2, np + 2 + n2, dp + 1, n2, scratch);
71 qhl += mpn_add_1 (qp1 + n2, qp1 + n2, n2,
72 mpn_dc_div_3_by_2 (qp1, np + 2, dp + 1, n2, scratch));
74 cc = mpn_submul_1 (np + 1, qp1, n - 1, dp[0]);
75 cc = mpn_sub_1 (np + n, np + n, 1, cc);
77 cc += mpn_sub_1 (np + n, np + n, 1, dp[0]);
80 qhl -= mpn_sub_1 (qp1, qp1, n - 1, (mp_limb_t) 1);
81 cc -= mpn_add_n (np + 1, np + 1, dp, n);
83 qhl += mpn_add_1 (qp1, qp1, n - 1,
84 mpn_sb_divrem_mn (qp, np, n + 1, dp, n));
88 qhl = mpn_dc_div_3_by_2 (qp + n2, np + n2, dp, n2, scratch);
89 qhl += mpn_add_1 (qp + n2, qp + n2, n2,
90 mpn_dc_div_3_by_2 (qp, np, dp, n2, scratch));
96 /* divides (np, 3n) by (dp, 2n) and puts the quotient in (qp, n),
97 the remainder in (np, 2n) */
100 mpn_dc_div_3_by_2 (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n, mp_ptr scratch)
102 mp_size_t twon = n + n;
105 if (n < DIV_DC_THRESHOLD)
106 qhl = mpn_sb_divrem_mn (qp, np + n, twon, dp + n, n);
108 qhl = mpn_dc_div_2_by_1 (qp, np + n, dp + n, n, scratch);
110 mpn_mul_n (scratch, qp, dp, n);
111 cc = mpn_sub_n (np, np, scratch, twon);
114 cc += mpn_sub_n (np + n, np + n, dp, n);
117 qhl -= mpn_sub_1 (qp, qp, n, (mp_limb_t) 1);
118 cc -= mpn_add_n (np, np, dp, twon);