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 https://opensource.org/licenses/CDDL-1.0.
  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 #include <sys/zio_compress.h>
  36
  37 static size_t
  38 zfs_zle_compress_buf(void *s_start, void *d_start, size_t s_len,
  39     size_t d_len, int n)
  40 {
  41         uchar_t *src = s_start;
  42         uchar_t *dst = d_start;
  43         uchar_t *s_end = src + s_len;
  44         uchar_t *d_end = dst + d_len;
  45
  46         while (src < s_end && dst < d_end - 1) {
  47                 uchar_t *first = src;
  48                 uchar_t *len = dst++;
  49                 if (src[0] == 0) {
  50                         uchar_t *last = src + (256 - n);
  51                         while (src < MIN(last, s_end) && src[0] == 0)
  52                                 src++;
  53                         *len = src - first - 1 + n;
  54                 } else {
  55                         uchar_t *last = src + n;
  56                         if (d_end - dst < n)
  57                                 break;
  58                         while (src < MIN(last, s_end) - 1 && (src[0] | src[1]))
  59                                 *dst++ = *src++;
  60                         if (src[0])
  61                                 *dst++ = *src++;
  62                         *len = src - first - 1;
  63                 }
  64         }
  65         return (src == s_end ? dst - (uchar_t *)d_start : s_len);
  66 }
  67
  68 static int
  69 zfs_zle_decompress_buf(void *s_start, void *d_start, size_t s_len,
  70     size_t d_len, int n)
  71 {
  72         uchar_t *src = s_start;
  73         uchar_t *dst = d_start;
  74         uchar_t *s_end = src + s_len;
  75         uchar_t *d_end = dst + d_len;
  76
  77         while (src < s_end && dst < d_end) {
  78                 int len = 1 + *src++;
  79                 if (len <= n) {
  80                         if (src + len > s_end || dst + len > d_end)
  81                                 return (-1);
  82                         while (len-- != 0)
  83                                 *dst++ = *src++;
  84                 } else {
  85                         len -= n;
  86                         if (dst + len > d_end)
  87                                 return (-1);
  88                         while (len-- != 0)
  89                                 *dst++ = 0;
  90                 }
  91         }
  92         return (dst == d_end ? 0 : -1);
  93 }
  94
  95 ZFS_COMPRESS_WRAP_DECL(zfs_zle_compress)
  96 ZFS_DECOMPRESS_WRAP_DECL(zfs_zle_decompress)