chiark / gitweb /
Shun time(), since on Linux it is not monotonic with gettimeofday().
[disorder] / lib / basen.c
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460b9539 1/*
2 * This file is part of DisOrder.
5aff007d 3 * Copyright (C) 2005, 2007, 2008 Richard Kettlewell
460b9539 4 *
e7eb3a27 5 * This program is free software: you can redistribute it and/or modify
460b9539 6 * it under the terms of the GNU General Public License as published by
e7eb3a27 7 * the Free Software Foundation, either version 3 of the License, or
460b9539 8 * (at your option) any later version.
e7eb3a27
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9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 *
460b9539 15 * You should have received a copy of the GNU General Public License
e7eb3a27 16 * along with this program. If not, see <http://www.gnu.org/licenses/>.
460b9539 17 */
14ad73b9
RK
18/** @file lib/basen.c @brief Arbitrary base conversion
19 *
20 * The functions in this file handle arbitrary-size non-negative integers,
21 * represented as a bigendian (MSW first) sequence of @c unsigned @c long
22 * words. The words themselves use the native byte order.
23 */
460b9539 24
05b75f8d 25#include "common.h"
460b9539 26
27#include "basen.h"
28
d7b6f0d1 29/** @brief Test whether v is 0
30 * @param v Pointer to bigendian bignum
31 * @param nwords Length of bignum
32 * @return !v
33 */
1c814807 34static int zero(const uint32_t *v, int nwords) {
460b9539 35 int n;
36
37 for(n = 0; n < nwords && !v[n]; ++n)
38 ;
39 return n == nwords;
40}
41
d7b6f0d1 42/** @brief Divide v by m returning the remainder.
43 * @param v Pointer to bigendian bignum
44 * @param nwords Length of bignum
45 * @param m Divisor (must not be 0)
46 * @return Remainder
47 *
48 * The quotient is stored in @p v.
49 */
1c814807 50static unsigned divide(uint32_t *v, int nwords, unsigned long m) {
460b9539 51 unsigned long r = 0, a, b;
52 int n;
53
54 /* we do the divide 16 bits at a time */
55 for(n = 0; n < nwords; ++n) {
56 a = v[n] >> 16;
57 b = v[n] & 0xFFFF;
58 a += r << 16;
59 r = a % m;
60 a /= m;
61 b += r << 16;
62 r = b % m;
63 b /= m;
64 v[n] = (a << 16) + b;
65 }
66 return r;
67}
68
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69/** @brief Multiple v by m and add a
70 * @param v Pointer to bigendian bignum
71 * @param nwords Length of bignum
72 * @param m Value to multiply by
73 * @param a Value to add
74 * @return 0 on success, non-0 on overflow
75 *
76 * Does v = m * v + a.
77 */
78static int mla(uint32_t *v, int nwords, uint32_t m, uint32_t a) {
79 int n = nwords - 1;
80 uint32_t carry = a;
81
82 while(n >= 0) {
83 const uint64_t p = (uint64_t)v[n] * m + carry;
84 carry = (uint32_t)(p >> 32);
85 v[n] = (uint32_t)p;
86 --n;
87 }
88 /* If there is still a carry then we overflowed */
89 return !!carry;
90}
91
92static const char basen_chars[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
93
d7b6f0d1 94/** @brief Convert v to a chosen base
abe28bfe 95 * @param v Pointer to bigendian bignum (modified!)
d7b6f0d1 96 * @param nwords Length of bignum
97 * @param buffer Output buffer
98 * @param bufsize Size of output buffer
99 * @param base Number base (2..62)
100 * @return 0 on success, -1 if the buffer is too small
101 *
102 * Converts @p v to a string in the given base using decimal digits, lower case
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103 * letters and upper case letters as digits.
104 *
105 * The inverse of nesab().
d7b6f0d1 106 */
1c814807 107int basen(uint32_t *v,
460b9539 108 int nwords,
109 char buffer[],
110 size_t bufsize,
111 unsigned base) {
112 size_t i = bufsize;
460b9539 113
114 do {
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115 if(i <= 1)
116 return -1; /* overflow */
1c814807 117 buffer[--i] = basen_chars[divide(v, nwords, base)];
460b9539 118 } while(!zero(v, nwords));
119 memmove(buffer, buffer + i, bufsize - i);
120 buffer[bufsize - i] = 0;
121 return 0;
122}
123
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124/** @brief Convert a string back to a large integer in an arbitrary base
125 * @param v Where to store result as a bigendian bignum
126 * @param nwords Space available in @p v
127 * @param s Input string
128 * @param base Number base (2..62)
129 * @return 0 on success, non-0 on overflow or invalid input
130 *
131 * The inverse of basen(). If the number is much smaller than the buffer then
132 * the first words will be 0.
133 */
134int nesab(uint32_t *v,
135 int nwords,
136 const char *s,
137 unsigned base) {
138 /* Initialize to 0 */
139 memset(v, 0, nwords * sizeof *v);
140 while(*s) {
141 const char *dp = strchr(basen_chars, *s++);
142 if(!dp)
143 return -1;
144 if(mla(v, nwords, base, dp - basen_chars))
145 return -1;
146 }
147 return 0;
148}
149
460b9539 150/*
151Local Variables:
152c-basic-offset:2
153comment-column:40
154fill-column:79
155End:
156*/