144 lines
3.7 KiB
C
144 lines
3.7 KiB
C
/* mpn_divexact(qp,np,nn,dp,dn,tp) -- Divide N = {np,nn} by D = {dp,dn} storing
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the result in Q = {qp,nn-dn+1} expecting no remainder. Overlap allowed
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between Q and N; all other overlap disallowed.
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Contributed to the GNU project by 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 Free Software Foundation, Inc.
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Copyright 2010, William Hart (modified for MPIR)
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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 3 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. If not, see http://www.gnu.org/licenses/. */
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#include "mpir.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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/* FIXME: the INV_DIV_Q_THRESHOLD should be replaced with a tuned cutoff specifically for this function */
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void
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mpn_divexact (mp_ptr qp,
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mp_srcptr np, mp_size_t nn,
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mp_srcptr dp, mp_size_t dn)
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{
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unsigned shift, shift2;
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int q_even;
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mp_size_t qn;
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mp_ptr tp, n2p, inv;
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mp_limb_t dinv, wp[2], cy;
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int extend = 0;
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TMP_DECL;
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ASSERT (dn > 0);
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ASSERT (nn >= dn);
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ASSERT (dp[dn-1] > 0);
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while (dp[0] == 0)
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{
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ASSERT (np[0] == 0);
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dp++;
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np++;
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dn--;
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nn--;
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}
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if (dn == 1)
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{
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MPN_DIVREM_OR_DIVEXACT_1 (qp, np, nn, dp[0]);
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return;
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}
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TMP_MARK;
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qn = nn + 1 - dn;
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count_trailing_zeros (shift, dp[0]);
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if ((BELOW_THRESHOLD (qn, INV_DIV_QR_THRESHOLD) && BELOW_THRESHOLD(dn, INV_DIV_QR_THRESHOLD)) || (dn <= 6))
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{
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if (shift > 0)
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{
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mp_size_t ss = (dn > qn) ? qn + 1 : dn;
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tp = TMP_ALLOC_LIMBS (ss);
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mpn_rshift (tp, dp, ss, shift);
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dp = tp;
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/* Since we have excluded dn == 1, we have nn > qn, and we need
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to shift one limb beyond qn. */
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n2p = TMP_ALLOC_LIMBS (qn + 1);
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mpn_rshift (n2p, np, qn + 1, shift);
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}
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else
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{
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n2p = TMP_ALLOC_LIMBS (qn);
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MPN_COPY (n2p, np, qn);
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}
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if (dn > qn)
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dn = qn;
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modlimb_invert(dinv, dp[0]);
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if (BELOW_THRESHOLD (dn, DC_BDIV_Q_THRESHOLD))
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mpn_sb_bdiv_q (qp, wp, n2p, qn, dp, dn, dinv);
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else
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mpn_dc_bdiv_q (qp, n2p, qn, dp, dn, dinv);
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} else
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{
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/* determine if the quotient is even */
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count_trailing_zeros (shift2, np[0]);
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q_even = ((np[0] == 0) || (shift2 > shift)) ? 1 : 0;
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if (dp[dn - 1] & GMP_LIMB_HIGHBIT)
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{
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n2p = TMP_ALLOC_LIMBS(nn);
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MPN_COPY(n2p, np, nn);
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} else
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{
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count_leading_zeros (shift, dp[dn - 1]);
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n2p = TMP_ALLOC_LIMBS(nn + 1);
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n2p[nn] = mpn_lshift(n2p, np, nn, shift);
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extend = (n2p[nn] != 0);
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nn += extend;
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tp = TMP_ALLOC_LIMBS(dn);
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mpn_lshift(tp, dp, dn, shift);
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dp = tp;
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}
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qn = nn - dn;
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if(qn)
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{
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inv = TMP_ALLOC_LIMBS(dn);
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mpn_invert(inv, dp, dn);
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cy = mpn_inv_divappr_q(qp, n2p, nn, dp, dn, inv);
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if (!extend) qp[qn] = cy;
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if ((qp[0] & 1) + q_even != 1) /* quotient is out by 1 */
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mpn_sub_1(qp, qp, qn + 1, 1);
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} else
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qp[0] = 1; /* as dp is normalised, exact division means qp = 1 */
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}
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TMP_FREE;
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}
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