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[disorder] / lib / basen.c
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460b9539 1/*
2 * This file is part of DisOrder.
3 * Copyright (C) 2005 Richard Kettlewell
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful, but
11 * WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
18 * USA
19 */
14ad73b9
RK
20/** @file lib/basen.c @brief Arbitrary base conversion
21 *
22 * The functions in this file handle arbitrary-size non-negative integers,
23 * represented as a bigendian (MSW first) sequence of @c unsigned @c long
24 * words. The words themselves use the native byte order.
25 */
460b9539 26
27#include <config.h>
28#include "types.h"
29
30#include <string.h>
31
32#include "basen.h"
33
d7b6f0d1 34/** @brief Test whether v is 0
35 * @param v Pointer to bigendian bignum
36 * @param nwords Length of bignum
37 * @return !v
38 */
460b9539 39static int zero(const unsigned long *v, int nwords) {
40 int n;
41
42 for(n = 0; n < nwords && !v[n]; ++n)
43 ;
44 return n == nwords;
45}
46
d7b6f0d1 47/** @brief Divide v by m returning the remainder.
48 * @param v Pointer to bigendian bignum
49 * @param nwords Length of bignum
50 * @param m Divisor (must not be 0)
51 * @return Remainder
52 *
53 * The quotient is stored in @p v.
54 */
460b9539 55static unsigned divide(unsigned long *v, int nwords, unsigned long m) {
56 unsigned long r = 0, a, b;
57 int n;
58
59 /* we do the divide 16 bits at a time */
60 for(n = 0; n < nwords; ++n) {
61 a = v[n] >> 16;
62 b = v[n] & 0xFFFF;
63 a += r << 16;
64 r = a % m;
65 a /= m;
66 b += r << 16;
67 r = b % m;
68 b /= m;
69 v[n] = (a << 16) + b;
70 }
71 return r;
72}
73
d7b6f0d1 74/** @brief Convert v to a chosen base
75 * @param v Pointer to bigendian bignum
76 * @param nwords Length of bignum
77 * @param buffer Output buffer
78 * @param bufsize Size of output buffer
79 * @param base Number base (2..62)
80 * @return 0 on success, -1 if the buffer is too small
81 *
82 * Converts @p v to a string in the given base using decimal digits, lower case
83 * letter sand upper case letters as digits.
84 */
460b9539 85int basen(unsigned long *v,
86 int nwords,
87 char buffer[],
88 size_t bufsize,
89 unsigned base) {
90 size_t i = bufsize;
91 static const char chars[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
92
93 do {
94 if(i <= 1) return -1; /* overflow */
95 buffer[--i] = chars[divide(v, nwords, base)];
96 } while(!zero(v, nwords));
97 memmove(buffer, buffer + i, bufsize - i);
98 buffer[bufsize - i] = 0;
99 return 0;
100}
101
102/*
103Local Variables:
104c-basic-offset:2
105comment-column:40
106fill-column:79
107End:
108*/