crc32.c

/*
 * crc32.c
 *
 * Written by
 *  Spiro Trikaliotis <Spiro.Trikaliotis@gmx.de>
 *  Andreas Boose <viceteam@t-online.de>
 *
 * This file is part of VICE, the Versatile Commodore Emulator.
 * See README for copyright notice.
 *
 *  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.
 *
 */

#include "vice.h"

#include <stdio.h>

#include "archdep.h"
#include "crc32.h"
#include "lib.h"
#include "util.h"


#define CRC32_POLY  0xedb88320
static unsigned long crc32_table[256];
static int crc32_is_initialized = 0;

unsigned long crc32_buf(const char *buffer, unsigned int len)
{
    int i, j;
    unsigned long crc, c;
    const char *p;

    if (!crc32_is_initialized) {
        for (i = 0; i < 256; i++) {
            c = (unsigned long) i;
            for (j = 0; j < 8; j++)
                c = c & 1 ? CRC32_POLY ^ (c >> 1) : c >> 1;
            crc32_table[i] = c;
        }
        crc32_is_initialized = 1;
    }

    crc = 0xffffffff;
    for (p = buffer; len > 0; ++p, --len)
        crc = (crc >> 8) ^ crc32_table[(crc ^ *p) & 0xff];
    
    return ~crc;
}

unsigned long crc32_file(const char *filename)
{
    FILE *fd;
    char *buffer;
    unsigned int len;
    unsigned long crc = 0;

    if (util_check_null_string(filename) < 0)
        return 0;

    fd = fopen(filename, MODE_READ);

    if (fd == NULL)
        return 0;

    len = (unsigned int)util_file_length(fd);

    buffer = lib_malloc(len);

    if (fread(buffer, len, 1, fd) == 1)
        crc = crc32_buf(buffer, len);

    fclose(fd);
    lib_free(buffer);

    return crc;
}