kernel/fs/zfs/lzjb.c

   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 kernel/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  *         kernel/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/types.h>
  40 #include <sys/param.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     1024
  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;
  55         uchar_t *copymap = NULL;
  56         int copymask = 1 << (NBBY - 1);
  57         int mlen, offset, hash;
  58         uint16_t *hp;
  59         uint16_t lempel[LEMPEL_SIZE] = { 0 };
  60
  61         while (src < (uchar_t *)s_start + s_len) {
  62                 if ((copymask <<= 1) == (1 << NBBY)) {
  63                         if (dst >= (uchar_t *)d_start + d_len - 1 - 2 * NBBY)
  64                                 return (s_len);
  65                         copymask = 1;
  66                         copymap = dst;
  67                         *dst++ = 0;
  68                 }
  69                 if (src > (uchar_t *)s_start + s_len - MATCH_MAX) {
  70                         *dst++ = *src++;
  71                         continue;
  72                 }
  73                 hash = (src[0] << 16) + (src[1] << 8) + src[2];
  74                 hash += hash >> 9;
  75                 hash += hash >> 5;
  76                 hp = &lempel[hash & (LEMPEL_SIZE - 1)];
  77                 offset = (intptr_t)(src - *hp) & OFFSET_MASK;
  78                 *hp = (uint16_t)(uintptr_t)src;
  79                 cpy = src - offset;
  80                 if (cpy >= (uchar_t *)s_start && cpy != src &&
  81                     src[0] == cpy[0] && src[1] == cpy[1] && src[2] == cpy[2]) {
  82                         *copymap |= copymask;
  83                         for (mlen = MATCH_MIN; mlen < MATCH_MAX; mlen++)
  84                                 if (src[mlen] != cpy[mlen])
  85                                         break;
  86                         *dst++ = ((mlen - MATCH_MIN) << (NBBY - MATCH_BITS)) |
  87                             (offset >> NBBY);
  88                         *dst++ = (uchar_t)offset;
  89                         src += mlen;
  90                 } else {
  91                         *dst++ = *src++;
  92                 }
  93         }
  94         return (dst - (uchar_t *)d_start);
  95 }
  96
  97 /*ARGSUSED*/
  98 int
  99 lzjb_decompress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
 100 {
 101         uchar_t *src = s_start;
 102         uchar_t *dst = d_start;
 103         uchar_t *d_end = (uchar_t *)d_start + d_len;
 104         uchar_t *cpy;
 105         uchar_t copymap = 0;
 106         int copymask = 1 << (NBBY - 1);
 107
 108         while (dst < d_end) {
 109                 if ((copymask <<= 1) == (1 << NBBY)) {
 110                         copymask = 1;
 111                         copymap = *src++;
 112                 }
 113                 if (copymap & copymask) {
 114                         int mlen = (src[0] >> (NBBY - MATCH_BITS)) + MATCH_MIN;
 115                         int offset = ((src[0] << NBBY) | src[1]) & OFFSET_MASK;
 116                         src += 2;
 117                         if ((cpy = dst - offset) < (uchar_t *)d_start)
 118                                 return (-1);
 119                         while (--mlen >= 0 && dst < d_end)
 120                                 *dst++ = *cpy++;
 121                 } else {
 122                         *dst++ = *src++;
 123                 }
 124         }
 125         return (0);
 126 }