2 * This file is part of DisOrder.
3 * Copyright (C) 2005 Richard Kettlewell
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.
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.
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
20 /** @file lib/basen.c @brief Arbitrary base conversion
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.
34 /** @brief Test whether v is 0
35 * @param v Pointer to bigendian bignum
36 * @param nwords Length of bignum
39 static int zero(const unsigned long *v, int nwords) {
42 for(n = 0; n < nwords && !v[n]; ++n)
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)
53 * The quotient is stored in @p v.
55 static unsigned divide(unsigned long *v, int nwords, unsigned long m) {
56 unsigned long r = 0, a, b;
59 /* we do the divide 16 bits at a time */
60 for(n = 0; n < nwords; ++n) {
74 /** @brief Convert v to a chosen base
75 * @param v Pointer to bigendian bignum (modified!)
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
82 * Converts @p v to a string in the given base using decimal digits, lower case
83 * letter sand upper case letters as digits.
85 int basen(unsigned long *v,
91 static const char chars[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
95 return -1; /* overflow */
96 buffer[--i] = chars[divide(v, nwords, base)];
97 } while(!zero(v, nwords));
98 memmove(buffer, buffer + i, bufsize - i);
99 buffer[bufsize - i] = 0;