114 lines
2.7 KiB
C
114 lines
2.7 KiB
C
/* mpn_sb_bdiv_qr -- schoolbook Hensel division with precomputed inverse,
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returning quotient and remainder.
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Contributed to the GNU project by Niels Möller.
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THE FUNCTIONS IN THIS FILE ARE INTERNAL FUNCTIONS WITH MUTABLE INTERFACES.
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IT IS ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS
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ALMOST GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GMP RELEASE.
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Copyright 2006, 2009 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 a binary quotient of size qn = nn - dn.
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Output:
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Q = N * D^{-1} mod B^qn,
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R = (N - Q * D) * B^(-qn)
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Stores the dn least significant limbs of R at {np + nn - dn, dn},
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and returns the borrow from the subtraction N - Q*D.
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D must be odd. dinv is D^-1 mod B. */
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mp_limb_t
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mpn_sb_bdiv_qr (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, mp_limb_t dinv)
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{
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mp_size_t qn;
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mp_size_t i;
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mp_limb_t rh;
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mp_limb_t ql;
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ASSERT (dn > 0);
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ASSERT (nn > dn);
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ASSERT ((dp[0] & 1) != 0);
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ASSERT (((dinv * dp[0]) & GMP_NUMB_MASK) == 1);
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dinv = -dinv;
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qn = nn - dn;
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rh = 0;
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/* To complete the negation, this value is added to q. */
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ql = 1;
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while (qn > dn)
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{
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for (i = 0; i < dn; i++)
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{
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mp_limb_t q;
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q = dinv * np[i];
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qp[i] = ~q;
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np[i] = mpn_addmul_1 (np + i, dp, dn, q);
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}
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rh += mpn_add (np + dn, np + dn, qn, np, dn);
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ql = mpn_add_1 (qp, qp, dn, ql);
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qp += dn; qn -= dn;
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np += dn; nn -= dn;
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}
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for (i = 0; i < qn; i++)
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{
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mp_limb_t q;
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q = dinv * np[i];
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qp[i] = ~q;
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np[i] = mpn_addmul_1 (np + i, dp, dn, q);
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}
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rh += mpn_add_n (np + dn, np + dn, np, qn);
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ql = mpn_add_1 (qp, qp, qn, ql);
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if (UNLIKELY (ql > 0))
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{
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/* q == 0 */
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ASSERT (rh == 0);
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return 0;
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}
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else
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{
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mp_limb_t cy;
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cy = mpn_sub_n (np + qn, np + qn, dp, dn);
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ASSERT (cy >= rh);
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return cy - rh;
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}
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}
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