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Assume initial digits in a track name are a sort key even without the
[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 *
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 */
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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
05b75f8d 27#include "common.h"
460b9539 28
29#include "basen.h"
30
d7b6f0d1 31/** @brief Test whether v is 0
32 * @param v Pointer to bigendian bignum
33 * @param nwords Length of bignum
34 * @return !v
35 */
460b9539 36static int zero(const unsigned long *v, int nwords) {
37 int n;
38
39 for(n = 0; n < nwords && !v[n]; ++n)
40 ;
41 return n == nwords;
42}
43
d7b6f0d1 44/** @brief Divide v by m returning the remainder.
45 * @param v Pointer to bigendian bignum
46 * @param nwords Length of bignum
47 * @param m Divisor (must not be 0)
48 * @return Remainder
49 *
50 * The quotient is stored in @p v.
51 */
460b9539 52static unsigned divide(unsigned long *v, int nwords, unsigned long m) {
53 unsigned long r = 0, a, b;
54 int n;
55
56 /* we do the divide 16 bits at a time */
57 for(n = 0; n < nwords; ++n) {
58 a = v[n] >> 16;
59 b = v[n] & 0xFFFF;
60 a += r << 16;
61 r = a % m;
62 a /= m;
63 b += r << 16;
64 r = b % m;
65 b /= m;
66 v[n] = (a << 16) + b;
67 }
68 return r;
69}
70
d7b6f0d1 71/** @brief Convert v to a chosen base
abe28bfe 72 * @param v Pointer to bigendian bignum (modified!)
d7b6f0d1 73 * @param nwords Length of bignum
74 * @param buffer Output buffer
75 * @param bufsize Size of output buffer
76 * @param base Number base (2..62)
77 * @return 0 on success, -1 if the buffer is too small
78 *
79 * Converts @p v to a string in the given base using decimal digits, lower case
80 * letter sand upper case letters as digits.
81 */
460b9539 82int basen(unsigned long *v,
83 int nwords,
84 char buffer[],
85 size_t bufsize,
86 unsigned base) {
87 size_t i = bufsize;
88 static const char chars[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
89
90 do {
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RK
91 if(i <= 1)
92 return -1; /* overflow */
460b9539 93 buffer[--i] = chars[divide(v, nwords, base)];
94 } while(!zero(v, nwords));
95 memmove(buffer, buffer + i, bufsize - i);
96 buffer[bufsize - i] = 0;
97 return 0;
98}
99
100/*
101Local Variables:
102c-basic-offset:2
103comment-column:40
104fill-column:79
105End:
106*/