xref: /titanic_52/usr/src/uts/common/fs/zfs/zle.c (revision 500b1e787b108592a37e3d54dc9b5e676de5386d)
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 2009 Sun Microsystems, Inc.  All rights reserved.
24  * Use is subject to license terms.
25  */
26 
27 /*
28  * Zero-length encoding.  This is a fast and simple algorithm to eliminate
29  * runs of zeroes.  Each chunk of compressed data begins with a length byte, b.
30  * If b < n (where n is the compression parameter) then the next b + 1 bytes
31  * are literal values.  If b >= n then the next (256 - b + 1) bytes are zero.
32  */
33 #include <sys/types.h>
34 #include <sys/sysmacros.h>
35 
36 size_t
37 zle_compress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
38 {
39 	uchar_t *src = s_start;
40 	uchar_t *dst = d_start;
41 	uchar_t *s_end = src + s_len;
42 	uchar_t *d_end = dst + d_len;
43 
44 	while (src < s_end && dst < d_end - 1) {
45 		uchar_t *first = src;
46 		uchar_t *len = dst++;
47 		if (src[0] == 0) {
48 			uchar_t *last = src + (256 - n);
49 			while (src < MIN(last, s_end) && src[0] == 0)
50 				src++;
51 			*len = src - first - 1 + n;
52 		} else {
53 			uchar_t *last = src + n;
54 			if (d_end - dst < n)
55 				break;
56 			while (src < MIN(last, s_end) - 1 && (src[0] | src[1]))
57 				*dst++ = *src++;
58 			if (src[0])
59 				*dst++ = *src++;
60 			*len = src - first - 1;
61 		}
62 	}
63 	return (src == s_end ? dst - (uchar_t *)d_start : s_len);
64 }
65 
66 int
67 zle_decompress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
68 {
69 	uchar_t *src = s_start;
70 	uchar_t *dst = d_start;
71 	uchar_t *s_end = src + s_len;
72 	uchar_t *d_end = dst + d_len;
73 
74 	while (src < s_end && dst < d_end) {
75 		int len = 1 + *src++;
76 		if (len <= n) {
77 			while (len-- != 0)
78 				*dst++ = *src++;
79 		} else {
80 			len -= n;
81 			while (len-- != 0)
82 				*dst++ = 0;
83 		}
84 	}
85 	return (dst == d_end ? 0 : -1);
86 }
87