mirror of https://github.com/macssh/macssh.git
152 lines
3.9 KiB
C
Executable File
152 lines
3.9 KiB
C
Executable File
/* mpn_divrem_2 -- Divide natural numbers, producing both remainder and
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quotient. The divisor is two limbs.
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THIS FILE CONTAINS INTERNAL FUNCTIONS WITH MUTABLE INTERFACES. IT IS
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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 GNU MP
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RELEASE.
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Copyright (C) 1993, 1994, 1995, 1996, 1999, 2000 Free Software Foundation,
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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 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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#include "gmp.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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/* Divide num (NP/NSIZE) by den (DP/2) and write
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the NSIZE-2 least significant quotient limbs at QP
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and the 2 long remainder at NP. If QEXTRA_LIMBS is
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non-zero, generate that many fraction bits and append them after the
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other quotient limbs.
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Return the most significant limb of the quotient, this is always 0 or 1.
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Preconditions:
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0. NSIZE >= 2.
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1. The most significant bit of the divisor must be set.
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2. QP must either not overlap with the input operands at all, or
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QP + 2 >= NP must hold true. (This means that it's
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possible to put the quotient in the high part of NUM, right after the
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remainder in NUM.
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3. NSIZE >= 2, even if QEXTRA_LIMBS is non-zero. */
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mp_limb_t
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#if __STDC__
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mpn_divrem_2 (mp_ptr qp, mp_size_t qxn,
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mp_ptr np, mp_size_t nsize,
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mp_srcptr dp)
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#else
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mpn_divrem_2 (qp, qxn, np, nsize, dp)
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mp_ptr qp;
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mp_size_t qxn;
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mp_ptr np;
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mp_size_t nsize;
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mp_srcptr dp;
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#endif
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{
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mp_limb_t most_significant_q_limb = 0;
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mp_size_t i;
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mp_limb_t n1, n0, n2;
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mp_limb_t d1, d0;
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mp_limb_t d1inv;
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int have_preinv;
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np += nsize - 2;
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d1 = dp[1];
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d0 = dp[0];
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n1 = np[1];
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n0 = np[0];
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if (n1 >= d1 && (n1 > d1 || n0 >= d0))
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{
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sub_ddmmss (n1, n0, n1, n0, d1, d0);
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most_significant_q_limb = 1;
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}
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/* If multiplication is much faster than division, preinvert the most
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significant divisor limb before entering the loop. */
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if (UDIV_TIME > 2 * UMUL_TIME + 6)
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{
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have_preinv = 0;
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if ((UDIV_TIME - (2 * UMUL_TIME + 6)) * (nsize - 2) > UDIV_TIME)
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{
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invert_limb (d1inv, d1);
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have_preinv = 1;
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}
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}
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for (i = qxn + nsize - 2 - 1; i >= 0; i--)
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{
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mp_limb_t q;
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mp_limb_t r;
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if (i >= qxn)
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np--;
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else
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np[0] = 0;
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if (n1 == d1)
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{
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/* Q should be either 111..111 or 111..110. Need special treatment
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of this rare case as normal division would give overflow. */
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q = ~(mp_limb_t) 0;
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r = n0 + d1;
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if (r < d1) /* Carry in the addition? */
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{
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add_ssaaaa (n1, n0, r - d0, np[0], 0, d0);
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qp[i] = q;
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continue;
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}
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n1 = d0 - (d0 != 0);
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n0 = -d0;
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}
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else
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{
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if (UDIV_TIME > 2 * UMUL_TIME + 6 && have_preinv)
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udiv_qrnnd_preinv (q, r, n1, n0, d1, d1inv);
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else
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udiv_qrnnd (q, r, n1, n0, d1);
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umul_ppmm (n1, n0, d0, q);
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}
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n2 = np[0];
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q_test:
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if (n1 > r || (n1 == r && n0 > n2))
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{
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/* The estimated Q was too large. */
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q--;
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sub_ddmmss (n1, n0, n1, n0, 0, d0);
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r += d1;
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if (r >= d1) /* If not carry, test Q again. */
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goto q_test;
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}
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qp[i] = q;
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sub_ddmmss (n1, n0, r, n2, n1, n0);
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}
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np[1] = n1;
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np[0] = n0;
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return most_significant_q_limb;
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}
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