124 lines
3.7 KiB
C
124 lines
3.7 KiB
C
/* mpn_dc_divrem_n and auxilliary routines.
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THE FUNCTIONS IN THIS FILE ARE INTERNAL FUNCTIONS WITH MUTABLE
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INTERFACES. IT IS ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.
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IN FACT, IT IS ALMOST GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A
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FUTURE GNU MP RELEASE.
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Copyright 2000, 2001, 2002, 2004, 2005 Free Software Foundation, Inc.
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Contributed by Paul Zimmermann.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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/*
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[1] Fast Recursive Division, by Christoph Burnikel and Joachim Ziegler,
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Technical report MPI-I-98-1-022, october 1998.
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http://www.mpi-sb.mpg.de/~ziegler/TechRep.ps.gz
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*/
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static mp_limb_t mpn_dc_div_3_by_2
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_PROTO ((mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n, mp_ptr scratch));
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static mp_limb_t mpn_dc_div_2_by_1
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_PROTO ((mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n, mp_ptr scratch));
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/* mpn_dc_divrem_n - Implements algorithm of page 8 in [1]: divides (np,2n)
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by (dp,n) and puts the quotient in (qp,n), the remainder in (np,n).
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Returns most significant limb of the quotient, which is 0 or 1.
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Requires that the most significant bit of the divisor is set. */
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mp_limb_t
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mpn_dc_divrem_n (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n)
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{
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mp_limb_t ret;
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mp_ptr scratch;
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TMP_DECL;
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TMP_MARK;
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scratch = TMP_ALLOC_LIMBS (n);
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ret = mpn_dc_div_2_by_1 (qp, np, dp, n, scratch);
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TMP_FREE;
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return ret;
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}
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static mp_limb_t
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mpn_dc_div_2_by_1 (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n, mp_ptr scratch)
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{
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mp_limb_t qhl, cc;
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mp_size_t n2 = n/2;
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if (n % 2 != 0)
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{
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mp_ptr qp1 = qp + 1;
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qhl = mpn_dc_div_3_by_2 (qp1 + n2, np + 2 + n2, dp + 1, n2, scratch);
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qhl += mpn_add_1 (qp1 + n2, qp1 + n2, n2,
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mpn_dc_div_3_by_2 (qp1, np + 2, dp + 1, n2, scratch));
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cc = mpn_submul_1 (np + 1, qp1, n - 1, dp[0]);
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cc = mpn_sub_1 (np + n, np + n, 1, cc);
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if (qhl != 0)
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cc += mpn_sub_1 (np + n, np + n, 1, dp[0]);
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while (cc != 0)
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{
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qhl -= mpn_sub_1 (qp1, qp1, n - 1, (mp_limb_t) 1);
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cc -= mpn_add_n (np + 1, np + 1, dp, n);
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}
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qhl += mpn_add_1 (qp1, qp1, n - 1,
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mpn_sb_divrem_mn (qp, np, n + 1, dp, n));
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}
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else
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{
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qhl = mpn_dc_div_3_by_2 (qp + n2, np + n2, dp, n2, scratch);
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qhl += mpn_add_1 (qp + n2, qp + n2, n2,
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mpn_dc_div_3_by_2 (qp, np, dp, n2, scratch));
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}
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return qhl;
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}
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/* divides (np, 3n) by (dp, 2n) and puts the quotient in (qp, n),
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the remainder in (np, 2n) */
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static mp_limb_t
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mpn_dc_div_3_by_2 (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n, mp_ptr scratch)
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{
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mp_size_t twon = n + n;
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mp_limb_t qhl, cc;
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if (n < DIV_DC_THRESHOLD)
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qhl = mpn_sb_divrem_mn (qp, np + n, twon, dp + n, n);
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else
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qhl = mpn_dc_div_2_by_1 (qp, np + n, dp + n, n, scratch);
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mpn_mul_n (scratch, qp, dp, n);
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cc = mpn_sub_n (np, np, scratch, twon);
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if (qhl != 0)
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cc += mpn_sub_n (np + n, np + n, dp, n);
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while (cc != 0)
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{
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qhl -= mpn_sub_1 (qp, qp, n, (mp_limb_t) 1);
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cc -= mpn_add_n (np, np, dp, twon);
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}
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return qhl;
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}
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