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      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	"@(#)lzjb.c	1.3	07/03/22 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 #include <sys/types.h>
     41 
     42 #define	MATCH_BITS	6
     43 #define	MATCH_MIN	3
     44 #define	MATCH_MAX	((1 << MATCH_BITS) + (MATCH_MIN - 1))
     45 #define	OFFSET_MASK	((1 << (16 - MATCH_BITS)) - 1)
     46 #define	LEMPEL_SIZE	256
     47 
     48 /*ARGSUSED*/
     49 size_t
     50 lzjb_compress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
     51 {
     52 	uchar_t *src = s_start;
     53 	uchar_t *dst = d_start;
     54 	uchar_t *cpy, *copymap;
     55 	int copymask = 1 << (NBBY - 1);
     56 	int mlen, offset;
     57 	uint16_t *hp;
     58 	uint16_t lempel[LEMPEL_SIZE];	/* uninitialized; see above */
     59 
     60 	while (src < (uchar_t *)s_start + s_len) {
     61 		if ((copymask <<= 1) == (1 << NBBY)) {
     62 			if (dst >= (uchar_t *)d_start + d_len - 1 - 2 * NBBY) {
     63 				if (d_len != s_len)
     64 					return (s_len);
     65 				mlen = s_len;
     66 				for (src = s_start, dst = d_start; mlen; mlen--)
     67 					*dst++ = *src++;
     68 				return (s_len);
     69 			}
     70 			copymask = 1;
     71 			copymap = dst;
     72 			*dst++ = 0;
     73 		}
     74 		if (src > (uchar_t *)s_start + s_len - MATCH_MAX) {
     75 			*dst++ = *src++;
     76 			continue;
     77 		}
     78 		hp = &lempel[((src[0] + 13) ^ (src[1] - 13) ^ src[2]) &
     79 		    (LEMPEL_SIZE - 1)];
     80 		offset = (intptr_t)(src - *hp) & OFFSET_MASK;
     81 		*hp = (uint16_t)(uintptr_t)src;
     82 		cpy = src - offset;
     83 		if (cpy >= (uchar_t *)s_start && cpy != src &&
     84 		    src[0] == cpy[0] && src[1] == cpy[1] && src[2] == cpy[2]) {
     85 			*copymap |= copymask;
     86 			for (mlen = MATCH_MIN; mlen < MATCH_MAX; mlen++)
     87 				if (src[mlen] != cpy[mlen])
     88 					break;
     89 			*dst++ = ((mlen - MATCH_MIN) << (NBBY - MATCH_BITS)) |
     90 			    (offset >> NBBY);
     91 			*dst++ = (uchar_t)offset;
     92 			src += mlen;
     93 		} else {
     94 			*dst++ = *src++;
     95 		}
     96 	}
     97 	return (dst - (uchar_t *)d_start);
     98 }
     99 
    100 /*ARGSUSED*/
    101 int
    102 lzjb_decompress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
    103 {
    104 	uchar_t *src = s_start;
    105 	uchar_t *dst = d_start;
    106 	uchar_t *d_end = (uchar_t *)d_start + d_len;
    107 	uchar_t *cpy, copymap;
    108 	int copymask = 1 << (NBBY - 1);
    109 
    110 	while (dst < d_end) {
    111 		if ((copymask <<= 1) == (1 << NBBY)) {
    112 			copymask = 1;
    113 			copymap = *src++;
    114 		}
    115 		if (copymap & copymask) {
    116 			int mlen = (src[0] >> (NBBY - MATCH_BITS)) + MATCH_MIN;
    117 			int offset = ((src[0] << NBBY) | src[1]) & OFFSET_MASK;
    118 			src += 2;
    119 			if ((cpy = dst - offset) < (uchar_t *)d_start)
    120 				return (-1);
    121 			while (--mlen >= 0 && dst < d_end)
    122 				*dst++ = *cpy++;
    123 		} else {
    124 			*dst++ = *src++;
    125 		}
    126 	}
    127 	return (0);
    128 }
    129