2010-08-13 15:30:08 -04:00
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/* mpn_dc_bdiv_qr -- divide-and-conquer Hensel division with precomputed
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inverse, returning quotient and remainder.
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Contributed to the GNU project by Niels M<EFBFBD>ller 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, 2010 Free Software Foundation, Inc.
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Copyright 2010 William Hart (minor modifications)
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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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/* Computes Hensel binary division of {np, 2*n} by {dp, n}.
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Output:
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q = n * d^{-1} mod 2^{qn * GMP_NUMB_BITS},
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r = (n - q * d) * 2^{-qn * GMP_NUMB_BITS}
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Stores q at qp. Stores the n least significant limbs of r at the high half
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of np, and returns the borrow from the subtraction n - q*d.
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2014-02-14 18:25:39 -05:00
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d must be odd. dinv is d^-1 mod 2^GMP_NUMB_BITS.
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*/
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2010-08-13 15:30:08 -04:00
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mp_limb_t
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mpn_dc_bdiv_qr_n (mp_ptr qp, 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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mp_size_t lo, hi;
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mp_limb_t cy;
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mp_limb_t rh;
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2014-02-14 18:25:39 -05:00
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lo = n >> 1; /* floor(n/2) */
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hi = n - lo; /* ceil(n/2) */
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2010-08-13 15:30:08 -04:00
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if (BELOW_THRESHOLD (lo, DC_BDIV_QR_THRESHOLD))
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cy = mpn_sb_bdiv_qr (qp, np, 2 * lo, dp, lo, dinv);
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else
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cy = mpn_dc_bdiv_qr_n (qp, np, dp, lo, dinv, tp);
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mpn_mul (tp, dp + lo, hi, qp, lo);
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mpn_incr_u (tp + lo, cy);
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rh = mpn_sub (np + lo, np + lo, n + hi, tp, n);
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if (BELOW_THRESHOLD (hi, DC_BDIV_QR_THRESHOLD))
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cy = mpn_sb_bdiv_qr (qp + lo, np + lo, 2 * hi, dp, hi, dinv);
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else
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cy = mpn_dc_bdiv_qr_n (qp + lo, np + lo, dp, hi, dinv, tp);
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mpn_mul (tp, qp + lo, hi, dp + hi, lo);
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mpn_incr_u (tp + hi, cy);
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rh += mpn_sub_n (np + n, np + n, tp, n);
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return rh;
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}
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