lzjb.c

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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 "%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 }

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FreeBSD/Linux Kernel Cross Reference sys/cddl/boot/zfs/lzjb.c

FreeBSD/Linux Kernel Cross Reference
sys/cddl/boot/zfs/lzjb.c