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1.1 maekawa 1: /* mpn_udiv_w_sdiv -- implement udiv_qrnnd on machines with only signed
2: division.
3:
4: Contributed by Peter L. Montgomery.
5:
1.1.1.2 ! maekawa 6: THIS IS AN INTERNAL FUNCTION WITH A MUTABLE INTERFACE. IT IS ONLY SAFE
! 7: TO REACH THIS FUNCTION THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS
! 8: ALMOST GUARANTEED THAT THIS FUNCTION WILL CHANGE OR DISAPPEAR IN A FUTURE
! 9: GNU MP RELEASE.
! 10:
! 11:
! 12: Copyright (C) 1992, 1994, 1996, 2000 Free Software Foundation, Inc.
1.1 maekawa 13:
14: This file is part of the GNU MP Library.
15:
16: The GNU MP Library is free software; you can redistribute it and/or modify
1.1.1.2 ! maekawa 17: it under the terms of the GNU Lesser General Public License as published by
! 18: the Free Software Foundation; either version 2.1 of the License, or (at your
1.1 maekawa 19: option) any later version.
20:
21: The GNU MP Library is distributed in the hope that it will be useful, but
22: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
1.1.1.2 ! maekawa 23: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
1.1 maekawa 24: License for more details.
25:
1.1.1.2 ! maekawa 26: You should have received a copy of the GNU Lesser General Public License
1.1 maekawa 27: along with the GNU MP Library; see the file COPYING.LIB. If not, write to
28: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
29: MA 02111-1307, USA. */
30:
31: #include "gmp.h"
32: #include "gmp-impl.h"
33: #include "longlong.h"
34:
35: mp_limb_t
36: mpn_udiv_w_sdiv (rp, a1, a0, d)
37: mp_limb_t *rp, a1, a0, d;
38: {
39: mp_limb_t q, r;
40: mp_limb_t c0, c1, b1;
41:
42: if ((mp_limb_signed_t) d >= 0)
43: {
44: if (a1 < d - a1 - (a0 >> (BITS_PER_MP_LIMB - 1)))
45: {
46: /* dividend, divisor, and quotient are nonnegative */
47: sdiv_qrnnd (q, r, a1, a0, d);
48: }
49: else
50: {
51: /* Compute c1*2^32 + c0 = a1*2^32 + a0 - 2^31*d */
52: sub_ddmmss (c1, c0, a1, a0, d >> 1, d << (BITS_PER_MP_LIMB - 1));
53: /* Divide (c1*2^32 + c0) by d */
54: sdiv_qrnnd (q, r, c1, c0, d);
55: /* Add 2^31 to quotient */
56: q += (mp_limb_t) 1 << (BITS_PER_MP_LIMB - 1);
57: }
58: }
59: else
60: {
61: b1 = d >> 1; /* d/2, between 2^30 and 2^31 - 1 */
62: c1 = a1 >> 1; /* A/2 */
63: c0 = (a1 << (BITS_PER_MP_LIMB - 1)) + (a0 >> 1);
64:
65: if (a1 < b1) /* A < 2^32*b1, so A/2 < 2^31*b1 */
66: {
67: sdiv_qrnnd (q, r, c1, c0, b1); /* (A/2) / (d/2) */
68:
69: r = 2*r + (a0 & 1); /* Remainder from A/(2*b1) */
70: if ((d & 1) != 0)
71: {
72: if (r >= q)
73: r = r - q;
74: else if (q - r <= d)
75: {
76: r = r - q + d;
77: q--;
78: }
79: else
80: {
81: r = r - q + 2*d;
82: q -= 2;
83: }
84: }
85: }
86: else if (c1 < b1) /* So 2^31 <= (A/2)/b1 < 2^32 */
87: {
88: c1 = (b1 - 1) - c1;
89: c0 = ~c0; /* logical NOT */
90:
91: sdiv_qrnnd (q, r, c1, c0, b1); /* (A/2) / (d/2) */
92:
93: q = ~q; /* (A/2)/b1 */
94: r = (b1 - 1) - r;
95:
96: r = 2*r + (a0 & 1); /* A/(2*b1) */
97:
98: if ((d & 1) != 0)
99: {
100: if (r >= q)
101: r = r - q;
102: else if (q - r <= d)
103: {
104: r = r - q + d;
105: q--;
106: }
107: else
108: {
109: r = r - q + 2*d;
110: q -= 2;
111: }
112: }
113: }
114: else /* Implies c1 = b1 */
115: { /* Hence a1 = d - 1 = 2*b1 - 1 */
116: if (a0 >= -d)
117: {
118: q = -1;
119: r = a0 + d;
120: }
121: else
122: {
123: q = -2;
124: r = a0 + 2*d;
125: }
126: }
127: }
128:
129: *rp = r;
130: return q;
131: }