Annotation of OpenXM_contrib/gmp/mpn/generic/bdivmod.c, Revision 1.1.1.1
1.1 maekawa 1: /* mpn/bdivmod.c: mpn_bdivmod for computing U/V mod 2^d.
2:
3: Copyright (C) 1991, 1993, 1994, 1995, 1996 Free Software Foundation, Inc.
4:
5: This file is part of the GNU MP Library.
6:
7: The GNU MP Library is free software; you can redistribute it and/or modify
8: it under the terms of the GNU Library General Public License as published by
9: the Free Software Foundation; either version 2 of the License, or (at your
10: option) any later version.
11:
12: The GNU MP Library is distributed in the hope that it will be useful, but
13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
15: License for more details.
16:
17: You should have received a copy of the GNU Library General Public License
18: along with the GNU MP Library; see the file COPYING.LIB. If not, write to
19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
20: MA 02111-1307, USA. */
21:
22: /* q_high = mpn_bdivmod (qp, up, usize, vp, vsize, d).
23:
24: Puts the low d/BITS_PER_MP_LIMB limbs of Q = U / V mod 2^d at qp, and
25: returns the high d%BITS_PER_MP_LIMB bits of Q as the result.
26:
27: Also, U - Q * V mod 2^(usize*BITS_PER_MP_LIMB) is placed at up. Since the
28: low d/BITS_PER_MP_LIMB limbs of this difference are zero, the code allows
29: the limb vectors at qp to overwrite the low limbs at up, provided qp <= up.
30:
31: Preconditions:
32: 1. V is odd.
33: 2. usize * BITS_PER_MP_LIMB >= d.
34: 3. If Q and U overlap, qp <= up.
35:
36: Ken Weber (kweber@mat.ufrgs.br, kweber@mcs.kent.edu)
37:
38: Funding for this work has been partially provided by Conselho Nacional
39: de Desenvolvimento Cienti'fico e Tecnolo'gico (CNPq) do Brazil, Grant
40: 301314194-2, and was done while I was a visiting reseacher in the Instituto
41: de Matema'tica at Universidade Federal do Rio Grande do Sul (UFRGS).
42:
43: References:
44: T. Jebelean, An algorithm for exact division, Journal of Symbolic
45: Computation, v. 15, 1993, pp. 169-180.
46:
47: K. Weber, The accelerated integer GCD algorithm, ACM Transactions on
48: Mathematical Software, v. 21 (March), 1995, pp. 111-122. */
49:
50: #include "gmp.h"
51: #include "gmp-impl.h"
52: #include "longlong.h"
53:
54: mp_limb_t
55: #if __STDC__
56: mpn_bdivmod (mp_ptr qp, mp_ptr up, mp_size_t usize,
57: mp_srcptr vp, mp_size_t vsize, unsigned long int d)
58: #else
59: mpn_bdivmod (qp, up, usize, vp, vsize, d)
60: mp_ptr qp;
61: mp_ptr up;
62: mp_size_t usize;
63: mp_srcptr vp;
64: mp_size_t vsize;
65: unsigned long int d;
66: #endif
67: {
68: /* Cache for v_inv is used to make mpn_accelgcd faster. */
69: static mp_limb_t previous_low_vlimb = 0;
70: static mp_limb_t v_inv; /* 1/V mod 2^BITS_PER_MP_LIMB. */
71:
72: if (vp[0] != previous_low_vlimb) /* Cache miss; compute v_inv. */
73: {
74: mp_limb_t v = previous_low_vlimb = vp[0];
75: mp_limb_t make_zero = 1;
76: mp_limb_t two_i = 1;
77: v_inv = 0;
78: do
79: {
80: while ((two_i & make_zero) == 0)
81: two_i <<= 1, v <<= 1;
82: v_inv += two_i;
83: make_zero -= v;
84: }
85: while (make_zero);
86: }
87:
88: /* Need faster computation for some common cases in mpn_accelgcd. */
89: if (usize == 2 && vsize == 2 &&
90: (d == BITS_PER_MP_LIMB || d == 2*BITS_PER_MP_LIMB))
91: {
92: mp_limb_t hi, lo;
93: mp_limb_t q = up[0] * v_inv;
94: umul_ppmm (hi, lo, q, vp[0]);
95: up[0] = 0, up[1] -= hi + q*vp[1], qp[0] = q;
96: if (d == 2*BITS_PER_MP_LIMB)
97: q = up[1] * v_inv, up[1] = 0, qp[1] = q;
98: return 0;
99: }
100:
101: /* Main loop. */
102: while (d >= BITS_PER_MP_LIMB)
103: {
104: mp_limb_t q = up[0] * v_inv;
105: mp_limb_t b = mpn_submul_1 (up, vp, MIN (usize, vsize), q);
106: if (usize > vsize)
107: mpn_sub_1 (up + vsize, up + vsize, usize - vsize, b);
108: d -= BITS_PER_MP_LIMB;
109: up += 1, usize -= 1;
110: *qp++ = q;
111: }
112:
113: if (d)
114: {
115: mp_limb_t b;
116: mp_limb_t q = (up[0] * v_inv) & (((mp_limb_t)1<<d) - 1);
117: switch (q)
118: {
119: case 0: return 0;
120: case 1: b = mpn_sub_n (up, up, vp, MIN (usize, vsize)); break;
121: default: b = mpn_submul_1 (up, vp, MIN (usize, vsize), q); break;
122: }
123: if (usize > vsize)
124: mpn_sub_1 (up + vsize, up + vsize, usize - vsize, b);
125: return q;
126: }
127:
128: return 0;
129: }
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