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/* 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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Copyright 2000, 2001 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., 59 Temple Place - Suite 330, Boston,
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MA 02111-1307, USA. */
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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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static mp_limb_t mpn_dc_div_3_halves_by_2
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_PROTO ((mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n));
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unused_mpn_divrem (qp, qxn, np, nn, dp, dn)
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/* This might be useful: */
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mp_ptr tp = alloca ((nn + qxn) * BYTES_PER_MP_LIMB);
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MPN_COPY (tp + qxn - nn, np, nn);
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c = mpn_divrem (qp, 0L, tp, nn + qxn, dp, dn);
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/* Maybe copy proper part of tp to np? Documentation is unclear about
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the returned np value when qxn != 0 */
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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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mpn_dc_divrem_n (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n)
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qhl = mpn_dc_divrem_n (qp + 1, np + 2, dp + 1, n - 1);
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cc = mpn_submul_1 (np + 1, qp + 1, n - 1, dp[0]);
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cc = mpn_sub_1 (np + n, np + n, 1, cc);
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if (qhl) cc += mpn_sub_1 (np + n, np + n, 1, dp[0]);
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qhl -= mpn_sub_1 (qp + 1, qp + 1, n - 1, (mp_limb_t) 1);
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cc -= mpn_add_n (np + 1, np + 1, dp, n);
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qhl += mpn_add_1 (qp + 1, qp + 1, n - 1,
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mpn_sb_divrem_mn (qp, np, n + 1, dp, n));
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qhl = mpn_dc_div_3_halves_by_2 (qp + n2, np + n2, dp, n2);
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qhl += mpn_add_1 (qp + n2, qp + n2, n2,
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mpn_dc_div_3_halves_by_2 (qp, np, dp, n2));
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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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mpn_dc_div_3_halves_by_2 (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n)
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mp_size_t twon = n + n;
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if (n < DC_THRESHOLD)
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qhl = mpn_sb_divrem_mn (qp, np + n, twon, dp + n, n);
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qhl = mpn_dc_divrem_n (qp, np + n, dp + n, n);
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tmp = (mp_ptr) TMP_ALLOC (twon * BYTES_PER_MP_LIMB);
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mpn_mul_n (tmp, qp, dp, n);
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cc = mpn_sub_n (np, np, tmp, twon);
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if (qhl) cc += mpn_sub_n (np + n, np + n, dp, n);
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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);