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/* base64.c -- Encode/decode integers in base64 format
* Created: Mon Sep 23 16:55:12 1996 by faith@cs.unc.edu
* Revised: Sun Nov 10 13:48:09 1996 by faith@cs.unc.edu
* Copyright 1996 Rickard E. Faith (faith@cs.unc.edu)
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Library General Public License as published
* by the Free Software Foundation; either version 2 of the License, or (at
* your option) any later version.
*
* This library 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
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
* $Id: base26.c,v 1.1 1996/11/10 20:20:46 faith Exp $
*
* \section{Base-26 Routines}
*
* \intro These routines perform encoding and decodingusing the 26
* lowercase characters, a-z. This is sometimes useful for generating
* unique identifiers that do not contain numbers.
*
*/
#include "maaP.h"
static unsigned char b26_list[] =
"abcdefghijklmnopqrstuvwxyz";
#define XX 100
static int b26_index[256] = {
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11,12,13,14,
15,16,17,18, 19,20,21,22, 23,24,25,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX,
};
/* |b26_encode| encodes |val| in a printable base 26 format. A MSB-first
encoding is generated. */
const char *b26_encode( unsigned long val )
{
static char result[8] = { 'a', 'a', 'a', 'a', 'a', 'a', 'a', '\0'};
static unsigned long previous = 0;
int i;
if (previous != val) {
previous = val;
for (i = 6; i >= 0; i--) {
result[i] = b26_list[ val % 26 ];
val = val / 26;
}
result[7] = 0;
}
for (i = 0; i < 6; i++) if (result[i] != b26_list[0]) return result + i;
return result + 6;
}
unsigned long b26_decode( const char *val )
{
unsigned long v = 0;
int i;
int offset = 1;
int len = strlen( val );
for (i = len - 1; i >= 0; i--) {
int tmp = b26_index[ (unsigned char)val[i] ];
if (tmp == XX)
err_internal( __FUNCTION__,
"Illegal character in base26 value: `%c' (%d)\n",
val[i], val[i] );
v += tmp * offset;
offset *= 26;
}
return v;
}
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