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// SPDX-License-Identifier: GPL-2.0-or-later
/* **************************************************************************
This program creates a CRC checksum and encodes the file that is named
in the command line.
Compile with: gcc encode_crc.c -Wall -o encode_crc
Author: Michael Margraf (michael.margraf@freecom.com)
Copyright: Freecom Technology GmbH, Berlin, 2004
www.freecom.com
************************************************************************* */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
// *******************************************************************
// CCITT polynom G(x)=x^16+x^12+x^5+1
#define POLYNOM 0x1021
// CRC algorithm with MSB first
int make_crc16(int crc, char new)
{
int i;
crc = crc ^ (((int)new) << 8);
for(i=0; i<8; i++) { // work on 8 bits in "new"
crc <<= 1; // MSBs first
if(crc & 0x10000) crc ^= POLYNOM;
}
return crc & 0xFFFF;
}
// *******************************************************************
// Reads the file "filename" into memory and returns pointer to the buffer.
static char *readfile(char *filename, int *size)
{
FILE *fp;
char *buffer;
struct stat info;
if (stat(filename,&info)!=0)
return NULL;
if ((fp=fopen(filename,"r"))==NULL)
return NULL;
buffer=NULL;
for (;;)
{
if ((buffer=(char *)malloc(info.st_size+1))==NULL)
break;
if (fread(buffer,1,info.st_size,fp)!=info.st_size)
{
free(buffer);
buffer=NULL;
break;
}
buffer[info.st_size]='\0';
if(size) *size = info.st_size;
break;
}
(void)fclose(fp);
return buffer;
}
// *******************************************************************
int main(int argc, char** argv)
{
if(argc < 3) {
printf("ERROR: Argument missing!\n\n");
return 1;
}
int count; // size of file in bytes
char *p, *master = readfile(argv[1], &count);
if(!master) {
printf("ERROR: File not found!\n");
return 1;
}
int crc = 0xFFFF, z;
p = master;
for(z=0; z<count; z++)
crc = make_crc16(crc, *(p++)); // calculate CRC
short crc16 = (short)crc;
/*
if(argc > 2) { // with flag for device recognition ?
p = argv[2];
for(z=strlen(p); z>0; z--) {
crc ^= (int)(*p);
*(p++) = (char)crc; // encode device flag
}
}
*/
p = master;
for(z=0; z<count; z++) {
crc ^= (int)(*p);
*(p++) = (char)crc; // encode file
}
// write encoded file...
FILE *fp = fopen(argv[2], "w");
if(!fp) {
printf("ERROR: File not writeable!\n");
return 1;
}
if(argc > 3) { // add flag for device recognition ?
fwrite(argv[3], strlen(argv[3]), sizeof(char), fp);
}
else {
// Device is an FSG, so byte swap (IXP4xx is big endian)
crc16 = ((crc16 >> 8) & 0xFF) | ((crc16 << 8) & 0xFF00);
}
fwrite(&crc16, 1, sizeof(short), fp); // first write CRC
fwrite(master, count, sizeof(char), fp); // write content
fclose(fp);
free(master);
return 0;
}
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