1/*
2 * $Id: updcrc.c,v 1.5 2009-10-13 22:55:36 didg Exp $
3 *
4 * updcrc(3), crc(1) - calculate crc polynomials
5 *
6 * Calculate, intelligently, the CRC of a dataset incrementally given a
7 * buffer full at a time.
8 *
9 * Usage:
10 * 	newcrc = updcrc( oldcrc, bufadr, buflen )
11 * 		unsigned int oldcrc, buflen;
12 * 		char *bufadr;
13 *
14 * Compiling with -DTEST creates a program to print the CRC of stdin to stdout.
15 * Compile with -DMAKETAB to print values for crctab to stdout.  If you change
16 *	the CRC polynomial parameters, be sure to do this and change
17 *	crctab's initial value.
18 *
19 * Notes:
20 *  Regards the data stream as an integer whose MSB is the MSB of the first
21 *  byte recieved.  This number is 'divided' (using xor instead of subtraction)
22 *  by the crc-polynomial P.
23 *  XMODEM does things a little differently, essentially treating the LSB of
24 * the first data byte as the MSB of the integer. Define SWAPPED to make
25 * things behave in this manner.
26 *
27 * Author:	Mark G. Mendel, 7/86
28 *		UUCP: ihnp4!umn-cs!hyper!mark, GEnie: mgm
29 */
30
31#ifdef HAVE_CONFIG_H
32#include "config.h"
33#endif /* HAVE_CONFIG_H */
34
35#include "updcrc.h"
36
37/* The CRC polynomial.
38 * These 4 values define the crc-polynomial.
39 * If you change them, you must change crctab[]'s initial value to what is
40 * printed by initcrctab() [see 'compile with -DMAKETAB' above].
41 */
42    /* Value used by:	    		CCITT	XMODEM	ARC  	*/
43#define	P	 0x1021	/* the poly:	0x1021	0x1021	A001	*/
44#define INIT_CRC 0L	/* init value:	-1	0	0	*/
45#if 0
46#define SWAPPED	/* bit order:	undef	defined	defined */
47#endif /* 0 */
48    /* the number of bits per char: don't change it. */
49#define B	8
50
51static WTYPE crctab[1<<B] = /* as calculated by initcrctab() */ {
520x0,  0x1021,  0x2042,  0x3063,  0x4084,  0x50a5,  0x60c6,  0x70e7,
530x8108,  0x9129,  0xa14a,  0xb16b,  0xc18c,  0xd1ad,  0xe1ce,  0xf1ef,
540x1231,  0x210,  0x3273,  0x2252,  0x52b5,  0x4294,  0x72f7,  0x62d6,
550x9339,  0x8318,  0xb37b,  0xa35a,  0xd3bd,  0xc39c,  0xf3ff,  0xe3de,
560x2462,  0x3443,  0x420,  0x1401,  0x64e6,  0x74c7,  0x44a4,  0x5485,
570xa56a,  0xb54b,  0x8528,  0x9509,  0xe5ee,  0xf5cf,  0xc5ac,  0xd58d,
580x3653,  0x2672,  0x1611,  0x630,  0x76d7,  0x66f6,  0x5695,  0x46b4,
590xb75b,  0xa77a,  0x9719,  0x8738,  0xf7df,  0xe7fe,  0xd79d,  0xc7bc,
600x48c4,  0x58e5,  0x6886,  0x78a7,  0x840,  0x1861,  0x2802,  0x3823,
610xc9cc,  0xd9ed,  0xe98e,  0xf9af,  0x8948,  0x9969,  0xa90a,  0xb92b,
620x5af5,  0x4ad4,  0x7ab7,  0x6a96,  0x1a71,  0xa50,  0x3a33,  0x2a12,
630xdbfd,  0xcbdc,  0xfbbf,  0xeb9e,  0x9b79,  0x8b58,  0xbb3b,  0xab1a,
640x6ca6,  0x7c87,  0x4ce4,  0x5cc5,  0x2c22,  0x3c03,  0xc60,  0x1c41,
650xedae,  0xfd8f,  0xcdec,  0xddcd,  0xad2a,  0xbd0b,  0x8d68,  0x9d49,
660x7e97,  0x6eb6,  0x5ed5,  0x4ef4,  0x3e13,  0x2e32,  0x1e51,  0xe70,
670xff9f,  0xefbe,  0xdfdd,  0xcffc,  0xbf1b,  0xaf3a,  0x9f59,  0x8f78,
680x9188,  0x81a9,  0xb1ca,  0xa1eb,  0xd10c,  0xc12d,  0xf14e,  0xe16f,
690x1080,  0xa1,  0x30c2,  0x20e3,  0x5004,  0x4025,  0x7046,  0x6067,
700x83b9,  0x9398,  0xa3fb,  0xb3da,  0xc33d,  0xd31c,  0xe37f,  0xf35e,
710x2b1,  0x1290,  0x22f3,  0x32d2,  0x4235,  0x5214,  0x6277,  0x7256,
720xb5ea,  0xa5cb,  0x95a8,  0x8589,  0xf56e,  0xe54f,  0xd52c,  0xc50d,
730x34e2,  0x24c3,  0x14a0,  0x481,  0x7466,  0x6447,  0x5424,  0x4405,
740xa7db,  0xb7fa,  0x8799,  0x97b8,  0xe75f,  0xf77e,  0xc71d,  0xd73c,
750x26d3,  0x36f2,  0x691,  0x16b0,  0x6657,  0x7676,  0x4615,  0x5634,
760xd94c,  0xc96d,  0xf90e,  0xe92f,  0x99c8,  0x89e9,  0xb98a,  0xa9ab,
770x5844,  0x4865,  0x7806,  0x6827,  0x18c0,  0x8e1,  0x3882,  0x28a3,
780xcb7d,  0xdb5c,  0xeb3f,  0xfb1e,  0x8bf9,  0x9bd8,  0xabbb,  0xbb9a,
790x4a75,  0x5a54,  0x6a37,  0x7a16,  0xaf1,  0x1ad0,  0x2ab3,  0x3a92,
800xfd2e,  0xed0f,  0xdd6c,  0xcd4d,  0xbdaa,  0xad8b,  0x9de8,  0x8dc9,
810x7c26,  0x6c07,  0x5c64,  0x4c45,  0x3ca2,  0x2c83,  0x1ce0,  0xcc1,
820xef1f,  0xff3e,  0xcf5d,  0xdf7c,  0xaf9b,  0xbfba,  0x8fd9,  0x9ff8,
830x6e17,  0x7e36,  0x4e55,  0x5e74,  0x2e93,  0x3eb2,  0xed1,  0x1ef0,
84} ;
85
86WTYPE
87updcrc(WTYPE icrc, unsigned char *icp, int icnt)
88{
89    register WTYPE crc = icrc;
90    register unsigned char *cp = icp;
91    register int cnt = icnt;
92
93    while( cnt-- ) {
94#ifndef SWAPPED
95	crc = (crc<<B) ^ crctab[(crc>>(W-B)) ^ *cp++];
96#else /* SWAPPED */
97	crc = (crc>>B) ^ crctab[(crc & ((1<<B)-1)) ^ *cp++];
98#endif /* SWAPPED */
99    }
100
101    return( crc );
102}
103
104#ifdef MAKETAB
105
106#include <stdio.h>
107int main(void)
108{
109    initcrctab();
110}
111
112void initcrctab(void)
113{
114    register  int b, i;
115    WTYPE v;
116
117
118    for( b = 0; b <= (1<<B)-1; ++b ) {
119#ifndef SWAPPED
120	for( v = b<<(W-B), i = B; --i >= 0; )
121	    v = v & ((WTYPE)1<<(W-1)) ? (v<<1)^P : v<<1;
122#else
123	for( v = b, i = B; --i >= 0; )
124	    v = v & 1 ? (v>>1)^P : v>>1;
125#endif
126	crctab[b] = v;
127
128	printf( "0x%lx,", v & ((1L<<W)-1L));
129	if( (b&7) == 7 )
130	    printf("\n" );
131	else
132	    printf("  ");
133    }
134}
135#endif /* MAKETAB */
136
137#ifdef TEST
138
139#include <stdio.h>
140#include <fcntl.h>
141
142#define MAXBUF	4096
143
144
145
146main( int ac, char **av)
147{
148    int fd;
149    int nr;
150    int i;
151    char buf[MAXBUF];
152    WTYPE crc, crc2;
153
154    fd = 0;
155    if( ac > 1 )
156	if( (fd = open( av[1], O_RDONLY )) < 0 ) {
157	    perror( av[1] );
158	    exit( -1 );
159	}
160    crc = crc2 = INIT_CRC;
161
162    while( (nr = read( fd, buf, MAXBUF )) > 0 ) {
163	crc = updcrc( crc, buf, nr );
164    }
165
166    if( nr != 0 )
167	perror( "reading" );
168    else {
169	printf( "%lx\n", crc );
170    }
171
172#ifdef MAGICCHECK
173    /* tack one's complement of crc onto data stream, and
174       continue crc calculation.  Should get a constant (magic number)
175       dependent only on P, not the data.
176     */
177    crc2 = crc ^ -1L;
178    for( nr = W-B; nr >= 0; nr -= B ) {
179	buf[0] = (crc2 >> nr);
180	crc = updcrc(crc, buf, 1);
181    }
182
183    /* crc should now equal magic */
184    buf[0] = buf[1] = buf[2] = buf[3] = 0;
185    printf( "magic test: %lx =?= %lx\n", crc, updcrc(-1, buf, W/B));
186#endif /* MAGICCHECK */
187}
188
189#endif /* TEST */
190