xref: /freebsd/sys/cddl/boot/zfs/lzjb.c (revision f39bffc62c1395bde25d152c7f68fdf7cbaab414)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 
22 /*
23  * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
24  * Use is subject to license terms.
25  */
26 
27 /*#pragma ident	"%Z%%M%	%I%	%E% SMI"*/
28 
29 /*
30  * We keep our own copy of this algorithm for 2 main reasons:
31  * 	1. If we didn't, anyone modifying common/os/compress.c would
32  *         directly break our on disk format
33  * 	2. Our version of lzjb does not have a number of checks that the
34  *         common/os version needs and uses
35  * In particular, we are adding the "feature" that compress() can
36  * take a destination buffer size and return -1 if the data will not
37  * compress to d_len or less.
38  */
39 
40 #define	MATCH_BITS	6
41 #define	MATCH_MIN	3
42 #define	MATCH_MAX	((1 << MATCH_BITS) + (MATCH_MIN - 1))
43 #define	OFFSET_MASK	((1 << (16 - MATCH_BITS)) - 1)
44 #define	LEMPEL_SIZE	256
45 
46 /*ARGSUSED*/
47 static int
48 lzjb_decompress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
49 {
50 	unsigned char *src = s_start;
51 	unsigned char *dst = d_start;
52 	unsigned char *d_end = (unsigned char *)d_start + d_len;
53 	unsigned char *cpy, copymap = 0;
54 	int copymask = 1 << (NBBY - 1);
55 
56 	while (dst < d_end) {
57 		if ((copymask <<= 1) == (1 << NBBY)) {
58 			copymask = 1;
59 			copymap = *src++;
60 		}
61 		if (copymap & copymask) {
62 			int mlen = (src[0] >> (NBBY - MATCH_BITS)) + MATCH_MIN;
63 			int offset = ((src[0] << NBBY) | src[1]) & OFFSET_MASK;
64 			src += 2;
65 			if ((cpy = dst - offset) < (unsigned char *)d_start)
66 				return (-1);
67 			while (--mlen >= 0 && dst < d_end)
68 				*dst++ = *cpy++;
69 		} else {
70 			*dst++ = *src++;
71 		}
72 	}
73 	return (0);
74 }
75