/*
* This file is part of DisOrder.
* Copyright (C) 2005, 2007, 2008 Richard Kettlewell
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
* USA
*/
/** @file lib/basen.c @brief Arbitrary base conversion
*
* The functions in this file handle arbitrary-size non-negative integers,
* represented as a bigendian (MSW first) sequence of @c unsigned @c long
* words. The words themselves use the native byte order.
*/
#include "common.h"
#include "basen.h"
/** @brief Test whether v is 0
* @param v Pointer to bigendian bignum
* @param nwords Length of bignum
* @return !v
*/
static int zero(const unsigned long *v, int nwords) {
int n;
for(n = 0; n < nwords && !v[n]; ++n)
;
return n == nwords;
}
/** @brief Divide v by m returning the remainder.
* @param v Pointer to bigendian bignum
* @param nwords Length of bignum
* @param m Divisor (must not be 0)
* @return Remainder
*
* The quotient is stored in @p v.
*/
static unsigned divide(unsigned long *v, int nwords, unsigned long m) {
unsigned long r = 0, a, b;
int n;
/* we do the divide 16 bits at a time */
for(n = 0; n < nwords; ++n) {
a = v[n] >> 16;
b = v[n] & 0xFFFF;
a += r << 16;
r = a % m;
a /= m;
b += r << 16;
r = b % m;
b /= m;
v[n] = (a << 16) + b;
}
return r;
}
/** @brief Convert v to a chosen base
* @param v Pointer to bigendian bignum (modified!)
* @param nwords Length of bignum
* @param buffer Output buffer
* @param bufsize Size of output buffer
* @param base Number base (2..62)
* @return 0 on success, -1 if the buffer is too small
*
* Converts @p v to a string in the given base using decimal digits, lower case
* letter sand upper case letters as digits.
*/
int basen(unsigned long *v,
int nwords,
char buffer[],
size_t bufsize,
unsigned base) {
size_t i = bufsize;
static const char chars[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
do {
if(i <= 1)
return -1; /* overflow */
buffer[--i] = chars[divide(v, nwords, base)];
} while(!zero(v, nwords));
memmove(buffer, buffer + i, bufsize - i);
buffer[bufsize - i] = 0;
return 0;
}
/*
Local Variables:
c-basic-offset:2
comment-column:40
fill-column:79
End:
*/