zle.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 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 size_t
   38 zle_compress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
   39 {
   40         uchar_t *src = s_start;
   41         uchar_t *dst = d_start;
   42         uchar_t *s_end = src + s_len;
   43         uchar_t *d_end = dst + d_len;
   44 
   45         while (src < s_end && dst < d_end - 1) {
   46                 uchar_t *first = src;
   47                 uchar_t *len = dst++;
   48                 if (src[0] == 0) {
   49                         uchar_t *last = src + (256 - n);
   50                         while (src < MIN(last, s_end) && src[0] == 0)
   51                                 src++;
   52                         *len = src - first - 1 + n;
   53                 } else {
   54                         uchar_t *last = src + n;
   55                         if (d_end - dst < n)
   56                                 break;
   57                         while (src < MIN(last, s_end) - 1 && (src[0] | src[1]))
   58                                 *dst++ = *src++;
   59                         if (src[0])
   60                                 *dst++ = *src++;
   61                         *len = src - first - 1;
   62                 }
   63         }
   64         return (src == s_end ? dst - (uchar_t *)d_start : s_len);
   65 }
   66 
   67 int
   68 zle_decompress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
   69 {
   70         uchar_t *src = s_start;
   71         uchar_t *dst = d_start;
   72         uchar_t *s_end = src + s_len;
   73         uchar_t *d_end = dst + d_len;
   74 
   75         while (src < s_end && dst < d_end) {
   76                 int len = 1 + *src++;
   77                 if (len <= n) {
   78                         if (src + len > s_end || dst + len > d_end)
   79                                 return (-1);
   80                         while (len-- != 0)
   81                                 *dst++ = *src++;
   82                 } else {
   83                         len -= n;
   84                         if (dst + len > d_end)
   85                                 return (-1);
   86                         while (len-- != 0)
   87                                 *dst++ = 0;
   88                 }
   89         }
   90         return (dst == d_end ? 0 : -1);
   91 }

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FreeBSD/Linux Kernel Cross Reference sys/contrib/openzfs/module/zfs/zle.c

FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/zle.c