module/zfs/zle.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 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                         if (src + len > s_end || dst + len > d_end)
  78                                 return (-1);
  79                         while (len-- != 0)
  80                                 *dst++ = *src++;
  81                 } else {
  82                         len -= n;
  83                         if (dst + len > d_end)
  84                                 return (-1);
  85                         while (len-- != 0)
  86                                 *dst++ = 0;
  87                 }
  88         }
  89         return (dst == d_end ? 0 : -1);
  90 }