1/* **************************************************************************
2
3   This program creates a CRC checksum and encodes the file that is named
4   in the command line.
5
6   Compile with:  gcc encode_crc.c -Wall -o encode_crc
7
8   Author:     Michael Margraf  (michael.margraf@freecom.com)
9   Copyright:  Freecom Technology GmbH, Berlin, 2004
10               www.freecom.com
11
12  This program is free software; you can redistribute it and/or modify
13  it under the terms of the GNU General Public License as published by
14  the Free Software Foundation; either version 2 of the License, or
15  (at your option) any later version.
16
17  This program is distributed in the hope that it will be useful,
18  but WITHOUT ANY WARRANTY; without even the implied warranty of
19  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
20  General Public License for more details.
21
22  You should have received a copy of the GNU General Public License
23  along with this program; if not, write to the Free Software
24  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
25
26 ************************************************************************* */
27
28
29#include <stdio.h>
30#include <stdlib.h>
31#include <string.h>
32#include <sys/stat.h>
33
34// *******************************************************************
35// CCITT polynom G(x)=x^16+x^12+x^5+1
36#define POLYNOM  0x1021
37
38// CRC algorithm with MSB first
39int make_crc16(int crc, char new)
40{
41  int i;
42  crc = crc ^ (((int)new) << 8);
43
44  for(i=0; i<8; i++) {  // work on 8 bits in "new"
45    crc <<= 1;          // MSBs first
46    if(crc & 0x10000)  crc ^= POLYNOM;
47  }
48  return crc & 0xFFFF;
49}
50
51// *******************************************************************
52// Reads the file "filename" into memory and returns pointer to the buffer.
53static char *readfile(char *filename, int *size)
54{
55	FILE		*fp;
56	char		*buffer;
57	struct stat	info;
58
59	if (stat(filename,&info)!=0)
60		return NULL;
61
62	if ((fp=fopen(filename,"r"))==NULL)
63		return NULL;
64
65	buffer=NULL;
66	for (;;)
67	{
68		if ((buffer=(char *)malloc(info.st_size+1))==NULL)
69			break;
70
71		if (fread(buffer,1,info.st_size,fp)!=info.st_size)
72		{
73			free(buffer);
74			buffer=NULL;
75			break;
76		}
77
78		buffer[info.st_size]='\0';
79		if(size) *size = info.st_size;
80
81		break;
82	}
83
84	(void)fclose(fp);
85
86	return buffer;
87}
88
89
90// *******************************************************************
91int main(int argc, char** argv)
92{
93  if(argc < 3) {
94    printf("ERROR: Argument missing!\n\n");
95    return 1;
96  }
97
98  int count;  // size of file in bytes
99  char *p, *master = readfile(argv[1], &count);
100  if(!master) {
101    printf("ERROR: File not found!\n");
102    return 1;
103  }
104
105  int crc = 0xFFFF, z;
106
107  p = master;
108  for(z=0; z<count; z++)
109    crc = make_crc16(crc, *(p++));  // calculate CRC
110  short crc16 = (short)crc;
111
112	/*
113  if(argc > 2) {   // with flag for device recognition ?
114    p = argv[2];
115    for(z=strlen(p); z>0; z--) {
116      crc ^= (int)(*p);
117      *(p++) = (char)crc;  // encode device flag
118    }
119  }
120	*/
121
122  p = master;
123  for(z=0; z<count; z++) {
124    crc ^= (int)(*p);
125    *(p++) = (char)crc;  // encode file
126  }
127
128
129  // write encoded file...
130  FILE *fp = fopen(argv[2], "w");
131  if(!fp) {
132    printf("ERROR: File not writeable!\n");
133    return 1;
134  }
135
136  if(argc > 3) {  // add flag for device recognition ?
137    fwrite(argv[3], strlen(argv[3]), sizeof(char), fp);
138  }
139  else {
140    // Device is an FSG, so byte swap (IXP4xx is big endian)
141    crc16 = ((crc16 >> 8) & 0xFF) | ((crc16 << 8) & 0xFF00);
142  }
143
144  fwrite(&crc16, 1, sizeof(short), fp);     // first write CRC
145
146  fwrite(master, count, sizeof(char), fp);  // write content
147  fclose(fp);
148
149  free(master);
150  return 0;
151}
152