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162 lines
3.7 KiB
C
162 lines
3.7 KiB
C
/* mpn_dcpi1_bdiv_q -- divide-and-conquer Hensel division with precomputed
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inverse, returning quotient.
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Contributed to the GNU project by Niels Möller and Torbjorn Granlund.
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THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES. IT IS ONLY
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SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
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GUARANTEED THAT THEY WILL CHANGE OR DISAPPEAR IN A FUTURE GMP RELEASE.
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Copyright 2006, 2007, 2009-2011, 2017 Free Software Foundation, Inc.
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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 either:
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* the GNU Lesser General Public License as published by the Free
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Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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or
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* the GNU General Public License as published by the Free Software
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Foundation; either version 2 of the License, or (at your option) any
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later version.
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or both in parallel, as here.
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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 General Public License
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for more details.
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You should have received copies of the GNU General Public License and the
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GNU Lesser General Public License along with the GNU MP Library. If not,
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see https://www.gnu.org/licenses/. */
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#include "gmp-impl.h"
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#if 0 /* unused, so leave out for now */
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static mp_size_t
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mpn_dcpi1_bdiv_q_n_itch (mp_size_t n)
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{
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/* NOTE: Depends on mullo_n and mpn_dcpi1_bdiv_qr_n interface */
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return n;
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}
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#endif
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/* Computes Q = - N / D mod B^n, destroys N.
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N = {np,n}
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D = {dp,n}
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*/
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static void
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mpn_dcpi1_bdiv_q_n (mp_ptr qp,
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mp_ptr np, mp_srcptr dp, mp_size_t n,
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mp_limb_t dinv, mp_ptr tp)
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{
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while (ABOVE_THRESHOLD (n, DC_BDIV_Q_THRESHOLD))
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{
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mp_size_t lo, hi;
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mp_limb_t cy;
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lo = n >> 1; /* floor(n/2) */
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hi = n - lo; /* ceil(n/2) */
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cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, lo, dinv, tp);
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mpn_mullo_n (tp, qp, dp + hi, lo);
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mpn_add_n (np + hi, np + hi, tp, lo);
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if (lo < hi)
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{
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cy += mpn_addmul_1 (np + lo, qp, lo, dp[lo]);
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np[n - 1] += cy;
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}
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qp += lo;
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np += lo;
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n -= lo;
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}
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mpn_sbpi1_bdiv_q (qp, np, n, dp, n, dinv);
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}
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/* Computes Q = - N / D mod B^nn, destroys N.
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N = {np,nn}
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D = {dp,dn}
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*/
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void
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mpn_dcpi1_bdiv_q (mp_ptr qp,
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mp_ptr np, mp_size_t nn,
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mp_srcptr dp, mp_size_t dn,
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mp_limb_t dinv)
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{
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mp_size_t qn;
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mp_limb_t cy;
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mp_ptr tp;
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TMP_DECL;
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TMP_MARK;
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ASSERT (dn >= 2);
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ASSERT (nn - dn >= 0);
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ASSERT (dp[0] & 1);
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tp = TMP_SALLOC_LIMBS (dn);
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qn = nn;
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if (qn > dn)
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{
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/* Reduce qn mod dn in a super-efficient manner. */
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do
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qn -= dn;
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while (qn > dn);
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/* Perform the typically smaller block first. */
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if (BELOW_THRESHOLD (qn, DC_BDIV_QR_THRESHOLD))
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cy = mpn_sbpi1_bdiv_qr (qp, np, 2 * qn, dp, qn, dinv);
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else
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cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, qn, dinv, tp);
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if (qn != dn)
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{
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if (qn > dn - qn)
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mpn_mul (tp, qp, qn, dp + qn, dn - qn);
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else
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mpn_mul (tp, dp + qn, dn - qn, qp, qn);
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mpn_incr_u (tp + qn, cy);
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mpn_add (np + qn, np + qn, nn - qn, tp, dn);
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cy = 0;
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}
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np += qn;
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qp += qn;
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qn = nn - qn;
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while (qn > dn)
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{
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mpn_add_1 (np + dn, np + dn, qn - dn, cy);
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cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, dn, dinv, tp);
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qp += dn;
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np += dn;
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qn -= dn;
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}
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mpn_dcpi1_bdiv_q_n (qp, np, dp, dn, dinv, tp);
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}
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else
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{
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if (BELOW_THRESHOLD (qn, DC_BDIV_Q_THRESHOLD))
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mpn_sbpi1_bdiv_q (qp, np, qn, dp, qn, dinv);
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else
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mpn_dcpi1_bdiv_q_n (qp, np, dp, qn, dinv, tp);
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}
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TMP_FREE;
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}
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