--- /dev/null
+/* mpn/bdivmod.c: mpn_bdivmod for computing U/V mod 2^d.
+
+Copyright (C) 1991, 1993, 1994, 1995, 1996 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Library General Public License as published by
+the Free Software Foundation; either version 2 of the License, or (at your
+option) any later version.
+
+The GNU MP Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
+License for more details.
+
+You should have received a copy of the GNU Library General Public License
+along with the GNU MP Library; see the file COPYING.LIB. If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+/* q_high = mpn_bdivmod (qp, up, usize, vp, vsize, d).
+
+ Puts the low d/BITS_PER_MP_LIMB limbs of Q = U / V mod 2^d at qp, and
+ returns the high d%BITS_PER_MP_LIMB bits of Q as the result.
+
+ Also, U - Q * V mod 2^(usize*BITS_PER_MP_LIMB) is placed at up. Since the
+ low d/BITS_PER_MP_LIMB limbs of this difference are zero, the code allows
+ the limb vectors at qp to overwrite the low limbs at up, provided qp <= up.
+
+ Preconditions:
+ 1. V is odd.
+ 2. usize * BITS_PER_MP_LIMB >= d.
+ 3. If Q and U overlap, qp <= up.
+
+ Ken Weber (kweber@mat.ufrgs.br, kweber@mcs.kent.edu)
+
+ Funding for this work has been partially provided by Conselho Nacional
+ de Desenvolvimento Cienti'fico e Tecnolo'gico (CNPq) do Brazil, Grant
+ 301314194-2, and was done while I was a visiting reseacher in the Instituto
+ de Matema'tica at Universidade Federal do Rio Grande do Sul (UFRGS).
+
+ References:
+ T. Jebelean, An algorithm for exact division, Journal of Symbolic
+ Computation, v. 15, 1993, pp. 169-180.
+
+ K. Weber, The accelerated integer GCD algorithm, ACM Transactions on
+ Mathematical Software, v. 21 (March), 1995, pp. 111-122. */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+mp_limb_t
+#if __STDC__
+mpn_bdivmod (mp_ptr qp, mp_ptr up, mp_size_t usize,
+ mp_srcptr vp, mp_size_t vsize, unsigned long int d)
+#else
+mpn_bdivmod (qp, up, usize, vp, vsize, d)
+ mp_ptr qp;
+ mp_ptr up;
+ mp_size_t usize;
+ mp_srcptr vp;
+ mp_size_t vsize;
+ unsigned long int d;
+#endif
+{
+ /* Cache for v_inv is used to make mpn_accelgcd faster. */
+ static mp_limb_t previous_low_vlimb = 0;
+ static mp_limb_t v_inv; /* 1/V mod 2^BITS_PER_MP_LIMB. */
+
+ if (vp[0] != previous_low_vlimb) /* Cache miss; compute v_inv. */
+ {
+ mp_limb_t v = previous_low_vlimb = vp[0];
+ mp_limb_t make_zero = 1;
+ mp_limb_t two_i = 1;
+ v_inv = 0;
+ do
+ {
+ while ((two_i & make_zero) == 0)
+ two_i <<= 1, v <<= 1;
+ v_inv += two_i;
+ make_zero -= v;
+ }
+ while (make_zero);
+ }
+
+ /* Need faster computation for some common cases in mpn_accelgcd. */
+ if (usize == 2 && vsize == 2 &&
+ (d == BITS_PER_MP_LIMB || d == 2*BITS_PER_MP_LIMB))
+ {
+ mp_limb_t hi, lo;
+ mp_limb_t q = up[0] * v_inv;
+ umul_ppmm (hi, lo, q, vp[0]);
+ up[0] = 0, up[1] -= hi + q*vp[1], qp[0] = q;
+ if (d == 2*BITS_PER_MP_LIMB)
+ q = up[1] * v_inv, up[1] = 0, qp[1] = q;
+ return 0;
+ }
+
+ /* Main loop. */
+ while (d >= BITS_PER_MP_LIMB)
+ {
+ mp_limb_t q = up[0] * v_inv;
+ mp_limb_t b = mpn_submul_1 (up, vp, MIN (usize, vsize), q);
+ if (usize > vsize)
+ mpn_sub_1 (up + vsize, up + vsize, usize - vsize, b);
+ d -= BITS_PER_MP_LIMB;
+ up += 1, usize -= 1;
+ *qp++ = q;
+ }
+
+ if (d)
+ {
+ mp_limb_t b;
+ mp_limb_t q = (up[0] * v_inv) & (((mp_limb_t)1<<d) - 1);
+ switch (q)
+ {
+ case 0: return 0;
+ case 1: b = mpn_sub_n (up, up, vp, MIN (usize, vsize)); break;
+ default: b = mpn_submul_1 (up, vp, MIN (usize, vsize), q); break;
+ }
+ if (usize > vsize)
+ mpn_sub_1 (up + vsize, up + vsize, usize - vsize, b);
+ return q;
+ }
+
+ return 0;
+}
projects / ghc-hetmet.git / blobdiff