1/*
2Copyright (C) 1999-2007 The Botan Project. All rights reserved.
3
4Redistribution and use in source and binary forms, for any use, with or without
5modification, is permitted provided that the following conditions are met:
6
71. Redistributions of source code must retain the above copyright notice, this
8list of conditions, and the following disclaimer.
9
102. Redistributions in binary form must reproduce the above copyright notice,
11this list of conditions, and the following disclaimer in the documentation
12and/or other materials provided with the distribution.
13
14THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) "AS IS" AND ANY EXPRESS OR IMPLIED
15WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
16MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ARE DISCLAIMED.
17
18IN NO EVENT SHALL THE AUTHOR(S) OR CONTRIBUTOR(S) BE LIABLE FOR ANY DIRECT,
19INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
20BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
22LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
23OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
24ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25*/
26// LICENSEHEADER_END
27namespace QCA { // WRAPNS_LINE
28/*************************************************
29 * Division Algorithm Source File *
30 * (C) 1999-2007 The Botan Project *
31 *************************************************/
32
33} // WRAPNS_LINE
34#include <botan/numthry.h>
35namespace QCA { // WRAPNS_LINE
36} // WRAPNS_LINE
37#include <botan/mp_core.h>
38namespace QCA { // WRAPNS_LINE
39
40namespace Botan {
41
42namespace {
43
44/*************************************************
45 * Handle signed operands, if necessary *
46 *************************************************/
47void sign_fixup(const BigInt &x, const BigInt &y, BigInt &q, BigInt &r)
48{
49 if (x.sign() == BigInt::Negative) {
50 q.flip_sign();
51 if (r.is_nonzero()) {
52 --q;
53 r = y.abs() - r;
54 }
55 }
56 if (y.sign() == BigInt::Negative)
57 q.flip_sign();
58}
59
60}
61
62/*************************************************
63 * Solve x = q * y + r *
64 *************************************************/
65void divide(const BigInt &x, const BigInt &y_arg, BigInt &q, BigInt &r)
66{
67 if (y_arg.is_zero())
68 throw BigInt::DivideByZero();
69
70 BigInt y = y_arg;
71 const u32bit y_words = y.sig_words();
72 r = x;
73
74 r.set_sign(BigInt::Positive);
75 y.set_sign(BigInt::Positive);
76
77 s32bit compare = r.cmp(y);
78
79 if (compare < 0)
80 q = 0;
81 else if (compare == 0) {
82 q = 1;
83 r = 0;
84 } else {
85 u32bit shifts = 0;
86 word y_top = y[y.sig_words() - 1];
87 while (y_top < MP_WORD_TOP_BIT) {
88 y_top <<= 1;
89 ++shifts;
90 }
91 y <<= shifts;
92 r <<= shifts;
93
94 const u32bit n = r.sig_words() - 1, t = y_words - 1;
95
96 q.get_reg().create(n: n - t + 1);
97 if (n <= t) {
98 while (r > y) {
99 r -= y;
100 q++;
101 }
102 r >>= shifts;
103 sign_fixup(x, y: y_arg, q, r);
104 return;
105 }
106
107 BigInt temp = y << (MP_WORD_BITS * (n - t));
108
109 while (r >= temp) {
110 r -= temp;
111 ++q[n - t];
112 }
113
114 for (u32bit j = n; j != t; --j) {
115 const word x_j0 = r.word_at(n: j);
116 const word x_j1 = r.word_at(n: j - 1);
117 const word y_t = y.word_at(n: t);
118
119 if (x_j0 == y_t)
120 q[j - t - 1] = MP_WORD_MAX;
121 else
122 q[j - t - 1] = bigint_divop(x_j0, x_j1, y_t);
123
124 while (bigint_divcore(q[j - t - 1], y_t, y.word_at(n: t - 1), x_j0, x_j1, r.word_at(n: j - 2)))
125 --q[j - t - 1];
126
127 r -= (q[j - t - 1] * y) << (MP_WORD_BITS * (j - t - 1));
128 if (r.is_negative()) {
129 r += y << (MP_WORD_BITS * (j - t - 1));
130 --q[j - t - 1];
131 }
132 }
133 r >>= shifts;
134 }
135
136 sign_fixup(x, y: y_arg, q, r);
137}
138
139}
140} // WRAPNS_LINE
141

source code of qca/src/botantools/botan/divide.cpp