rockbox/tools/scramble.c

/***************************************************************************
 *             __________               __   ___.
 *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
 *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
 *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
 *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 *                     \/            \/     \/    \/            \/
 * $Id$
 *
 * Copyright (C) 2002 by Bj<EFBFBD>rn Stenberg
 *
 * All files in this archive are subject to the GNU General Public License.
 * See the file COPYING in the source tree root for full license agreement.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ****************************************************************************/

#include <stdio.h>
#include <stdlib.h>

int main (int argc, char** argv)
{
    unsigned long length,i,slen;
    unsigned char *inbuf,*outbuf;
    unsigned short crc=0;
    unsigned char header[24];
    unsigned char *iname = argv[1];
    unsigned char *oname = argv[2];
    int headerlen = 6;
    FILE* file;

    if (argc < 3) {
       printf("usage: %s [-fm] <input file> <output file>\n",argv[0]);
       return -1;
    }

    if (argv[1][0] == '-') { /* assume any parameter is -fm :-) */
        headerlen = 24;
        iname = argv[2];
        oname = argv[3];
    }
    
    /* open file */
    file = fopen(iname,"rb");
    if (!file) {
       perror(iname);
       return -1;
    }
    fseek(file,0,SEEK_END);
    length = ftell(file);
    fseek(file,0,SEEK_SET); 
    inbuf = malloc(length);
    outbuf = malloc(length);
    if ( !inbuf || !outbuf ) {
       printf("out of memory!\n");
       return -1;
    }

    /* read file */
    i=fread(inbuf,1,length,file);
    if ( !i ) {
       perror(iname);
       return -1;
    }
    fclose(file);

    /* scramble */
    slen = length/4;
    for (i = 0; i < length; i++) {
       unsigned long addr = (i >> 2) + ((i % 4) * slen);
       unsigned char data = inbuf[i];
       data = ~((data << 1) | ((data >> 7) & 1)); /* poor man's ROL */
       outbuf[addr] = data;
    }
    
    /* calculate checksum */
    for (i=0;i<length;i++)
       crc += inbuf[i];

    /* make header */
    memset(header, 0, sizeof header);
    if (headerlen == 6) {
        header[0] = (length >> 24) & 0xff;
        header[1] = (length >> 16) & 0xff;
        header[2] = (length >> 8) & 0xff;
        header[3] = length & 0xff;
        header[4] = (crc >> 8) & 0xff;
        header[5] = crc & 0xff;
    }
    else {
        header[0] =
            header[1] =
            header[2] =
            header[3] = 0xff; /* ??? */
            
        header[6] = (crc >> 8) & 0xff;
        header[7] = crc & 0xff;

        header[11] = 4; /* ??? */

        header[15] = headerlen; /* really? */

        header[20] = (length >> 24) & 0xff;
        header[21] = (length >> 16) & 0xff;
        header[22] = (length >> 8) & 0xff;
        header[23] = length & 0xff;
    }

    /* write file */
    file = fopen(oname,"wb");
    if ( !file ) {
       perror(oname);
       return -1;
    }
    if ( !fwrite(header,headerlen,1,file) ) {
       perror(oname);
       return -1;
    }
    if ( !fwrite(outbuf,length,1,file) ) {
       perror(oname);
       return -1;
    }
    fclose(file);
    
    free(inbuf);
    free(outbuf);
    
    return 0;	
}