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 * Utility Functions Source File *
30 * (C) 1999-2007 The Botan Project *
31 *************************************************/
32
33} // WRAPNS_LINE
34#include <botan/util.h>
35namespace QCA { // WRAPNS_LINE
36#ifndef BOTAN_TOOLS_ONLY
37} // WRAPNS_LINE
38#include <botan/bit_ops.h>
39namespace QCA { // WRAPNS_LINE
40#endif
41} // WRAPNS_LINE
42#include <algorithm>
43namespace QCA { // WRAPNS_LINE
44} // WRAPNS_LINE
45#include <cmath>
46namespace QCA { // WRAPNS_LINE
47
48namespace Botan {
49
50/*************************************************
51 * Round up n to multiple of align_to *
52 *************************************************/
53u32bit round_up(u32bit n, u32bit align_to)
54{
55 if (n % align_to || n == 0)
56 n += align_to - (n % align_to);
57 return n;
58}
59
60/*************************************************
61 * Round down n to multiple of align_to *
62 *************************************************/
63u32bit round_down(u32bit n, u32bit align_to)
64{
65 return (n - (n % align_to));
66}
67
68#ifndef BOTAN_TOOLS_ONLY
69/*************************************************
70 * Return the work required for solving DL *
71 *************************************************/
72u32bit dl_work_factor(u32bit n_bits)
73{
74 const u32bit MIN_ESTIMATE = 64;
75
76 if (n_bits < 32)
77 return 0;
78
79 const double log_x = n_bits / 1.44;
80
81 u32bit estimate = (u32bit)(2.76 * std::pow(log_x, 1.0 / 3.0) * std::pow(std::log(log_x), 2.0 / 3.0));
82
83 return std::max(estimate, MIN_ESTIMATE);
84}
85
86/*************************************************
87 * Estimate the entropy of the buffer *
88 *************************************************/
89u32bit entropy_estimate(const byte buffer[], u32bit length)
90{
91 if (length <= 4)
92 return 0;
93
94 u32bit estimate = 0;
95 byte last = 0, last_delta = 0, last_delta2 = 0;
96
97 for (u32bit j = 0; j != length; ++j) {
98 byte delta = last ^ buffer[j];
99 last = buffer[j];
100
101 byte delta2 = delta ^ last_delta;
102 last_delta = delta;
103
104 byte delta3 = delta2 ^ last_delta2;
105 last_delta2 = delta2;
106
107 byte min_delta = delta;
108 if (min_delta > delta2)
109 min_delta = delta2;
110 if (min_delta > delta3)
111 min_delta = delta3;
112
113 estimate += hamming_weight(min_delta);
114 }
115
116 return (estimate / 2);
117}
118#endif
119
120}
121} // WRAPNS_LINE
122

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