6ec01646dc
BMakefiles and other bits will follow. Requested by: Andrey Chernov Made world by: Chuck Robey
130 lines
4.0 KiB
C
130 lines
4.0 KiB
C
/* mpn/bdivmod.c: mpn_bdivmod for computing U/V mod 2^d.
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Copyright (C) 1991, 1993, 1994, 1995, 1996 Free Software Foundation, 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 Library General Public License as published by
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the Free Software Foundation; either version 2 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 Library General Public
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License for more details.
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You should have received a copy of the GNU Library 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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/* q_high = mpn_bdivmod (qp, up, usize, vp, vsize, d).
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Puts the low d/BITS_PER_MP_LIMB limbs of Q = U / V mod 2^d at qp, and
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returns the high d%BITS_PER_MP_LIMB bits of Q as the result.
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Also, U - Q * V mod 2^(usize*BITS_PER_MP_LIMB) is placed at up. Since the
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low d/BITS_PER_MP_LIMB limbs of this difference are zero, the code allows
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the limb vectors at qp to overwrite the low limbs at up, provided qp <= up.
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Preconditions:
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1. V is odd.
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2. usize * BITS_PER_MP_LIMB >= d.
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3. If Q and U overlap, qp <= up.
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Ken Weber (kweber@mat.ufrgs.br, kweber@mcs.kent.edu)
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Funding for this work has been partially provided by Conselho Nacional
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de Desenvolvimento Cienti'fico e Tecnolo'gico (CNPq) do Brazil, Grant
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301314194-2, and was done while I was a visiting reseacher in the Instituto
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de Matema'tica at Universidade Federal do Rio Grande do Sul (UFRGS).
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References:
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T. Jebelean, An algorithm for exact division, Journal of Symbolic
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Computation, v. 15, 1993, pp. 169-180.
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K. Weber, The accelerated integer GCD algorithm, ACM Transactions on
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Mathematical Software, v. 21 (March), 1995, pp. 111-122. */
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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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mp_limb_t
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#if __STDC__
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mpn_bdivmod (mp_ptr qp, mp_ptr up, mp_size_t usize,
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mp_srcptr vp, mp_size_t vsize, unsigned long int d)
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#else
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mpn_bdivmod (qp, up, usize, vp, vsize, d)
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mp_ptr qp;
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mp_ptr up;
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mp_size_t usize;
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mp_srcptr vp;
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mp_size_t vsize;
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unsigned long int d;
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#endif
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{
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/* Cache for v_inv is used to make mpn_accelgcd faster. */
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static mp_limb_t previous_low_vlimb = 0;
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static mp_limb_t v_inv; /* 1/V mod 2^BITS_PER_MP_LIMB. */
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if (vp[0] != previous_low_vlimb) /* Cache miss; compute v_inv. */
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{
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mp_limb_t v = previous_low_vlimb = vp[0];
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mp_limb_t make_zero = 1;
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mp_limb_t two_i = 1;
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v_inv = 0;
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do
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{
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while ((two_i & make_zero) == 0)
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two_i <<= 1, v <<= 1;
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v_inv += two_i;
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make_zero -= v;
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}
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while (make_zero);
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}
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/* Need faster computation for some common cases in mpn_accelgcd. */
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if (usize == 2 && vsize == 2 &&
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(d == BITS_PER_MP_LIMB || d == 2*BITS_PER_MP_LIMB))
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{
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mp_limb_t hi, lo;
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mp_limb_t q = up[0] * v_inv;
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umul_ppmm (hi, lo, q, vp[0]);
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up[0] = 0, up[1] -= hi + q*vp[1], qp[0] = q;
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if (d == 2*BITS_PER_MP_LIMB)
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q = up[1] * v_inv, up[1] = 0, qp[1] = q;
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return 0;
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}
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/* Main loop. */
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while (d >= BITS_PER_MP_LIMB)
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{
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mp_limb_t q = up[0] * v_inv;
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mp_limb_t b = mpn_submul_1 (up, vp, MIN (usize, vsize), q);
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if (usize > vsize)
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mpn_sub_1 (up + vsize, up + vsize, usize - vsize, b);
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d -= BITS_PER_MP_LIMB;
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up += 1, usize -= 1;
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*qp++ = q;
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}
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if (d)
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{
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mp_limb_t b;
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mp_limb_t q = (up[0] * v_inv) & (((mp_limb_t)1<<d) - 1);
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switch (q)
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{
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case 0: return 0;
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case 1: b = mpn_sub_n (up, up, vp, MIN (usize, vsize)); break;
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default: b = mpn_submul_1 (up, vp, MIN (usize, vsize), q); break;
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}
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if (usize > vsize)
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mpn_sub_1 (up + vsize, up + vsize, usize - vsize, b);
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return q;
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}
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return 0;
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}
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