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 (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
24 */
25
26/*
27 * We keep our own copy of this algorithm for 3 main reasons:
28 *	1. If we didn't, anyone modifying common/os/compress.c would
29 *         directly break our on disk format
30 *	2. Our version of lzjb does not have a number of checks that the
31 *         common/os version needs and uses
32 *	3. We initialize the lempel to ensure deterministic results,
33 *	   so that identical blocks can always be deduplicated.
34 * In particular, we are adding the "feature" that compress() can
35 * take a destination buffer size and returns the compressed length, or the
36 * source length if compression would overflow the destination buffer.
37 */
38
39#include <sys/zfs_context.h>
40#include <sys/types.h>
41#include <sys/param.h>
42
43#define	MATCH_BITS	6
44#define	MATCH_MIN	3
45#define	MATCH_MAX	((1 << MATCH_BITS) + (MATCH_MIN - 1))
46#define	OFFSET_MASK	((1 << (16 - MATCH_BITS)) - 1)
47#define	LEMPEL_SIZE	1024
48
49/*ARGSUSED*/
50size_t
51lzjb_compress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
52{
53	uchar_t *src = s_start;
54	uchar_t *dst = d_start;
55	uchar_t *cpy;
56	uchar_t *copymap = NULL;
57	int copymask = 1 << (NBBY - 1);
58	int mlen, offset, hash;
59	uint16_t *hp;
60	uint16_t lempel[LEMPEL_SIZE] = { 0 };
61
62	while (src < (uchar_t *)s_start + s_len) {
63		if ((copymask <<= 1) == (1 << NBBY)) {
64			if (dst >= (uchar_t *)d_start + d_len - 1 - 2 * NBBY)
65				return (s_len);
66			copymask = 1;
67			copymap = dst;
68			*dst++ = 0;
69		}
70		if (src > (uchar_t *)s_start + s_len - MATCH_MAX) {
71			*dst++ = *src++;
72			continue;
73		}
74		hash = (src[0] << 16) + (src[1] << 8) + src[2];
75		hash += hash >> 9;
76		hash += hash >> 5;
77		hp = &lempel[hash & (LEMPEL_SIZE - 1)];
78		offset = (intptr_t)(src - *hp) & OFFSET_MASK;
79		*hp = (uint16_t)(uintptr_t)src;
80		cpy = src - offset;
81		if (cpy >= (uchar_t *)s_start && cpy != src &&
82		    src[0] == cpy[0] && src[1] == cpy[1] && src[2] == cpy[2]) {
83			*copymap |= copymask;
84			for (mlen = MATCH_MIN; mlen < MATCH_MAX; mlen++)
85				if (src[mlen] != cpy[mlen])
86					break;
87			*dst++ = ((mlen - MATCH_MIN) << (NBBY - MATCH_BITS)) |
88			    (offset >> NBBY);
89			*dst++ = (uchar_t)offset;
90			src += mlen;
91		} else {
92			*dst++ = *src++;
93		}
94	}
95	return (dst - (uchar_t *)d_start);
96}
97
98/*ARGSUSED*/
99int
100lzjb_decompress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
101{
102	uchar_t *src = s_start;
103	uchar_t *dst = d_start;
104	uchar_t *d_end = (uchar_t *)d_start + d_len;
105	uchar_t *cpy;
106	uchar_t copymap = 0;
107	int copymask = 1 << (NBBY - 1);
108
109	while (dst < d_end) {
110		if ((copymask <<= 1) == (1 << NBBY)) {
111			copymask = 1;
112			copymap = *src++;
113		}
114		if (copymap & copymask) {
115			int mlen = (src[0] >> (NBBY - MATCH_BITS)) + MATCH_MIN;
116			int offset = ((src[0] << NBBY) | src[1]) & OFFSET_MASK;
117			src += 2;
118			if ((cpy = dst - offset) < (uchar_t *)d_start)
119				return (-1);
120			if (mlen > (d_end - dst))
121				mlen = d_end - dst;
122			while (--mlen >= 0)
123				*dst++ = *cpy++;
124		} else {
125			*dst++ = *src++;
126		}
127	}
128	return (0);
129}
130