lzjb.c

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/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/types.h>

#define MATCH_BITS      6
#define MATCH_MIN       3
#define MATCH_MAX       ((1 << MATCH_BITS) + (MATCH_MIN - 1))
#define OFFSET_MASK     ((1 << (16 - MATCH_BITS)) - 1)
#define LEMPEL_SIZE     1024

/*ARGSUSED*/
size_t
lzjb_compress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
{
        uchar_t *src = s_start;
        uchar_t *dst = d_start;
        uchar_t *cpy, *copymap;
        int copymask = 1 << (NBBY - 1);
        int mlen, offset, hash;
        uint16_t *hp;
        uint16_t lempel[LEMPEL_SIZE] = { 0 };

        while (src < (uchar_t *)s_start + s_len) {
                if ((copymask <<= 1) == (1 << NBBY)) {
                        if (dst >= (uchar_t *)d_start + d_len - 1 - 2 * NBBY)
                                return (s_len);
                        copymask = 1;
                        copymap = dst;
                        *dst++ = 0;
                }
                if (src > (uchar_t *)s_start + s_len - MATCH_MAX) {
                        *dst++ = *src++;
                        continue;
                }
                hash = (src[0] << 16) + (src[1] << 8) + src[2];
                hash += hash >> 9;
                hash += hash >> 5;
                hp = &lempel[hash & (LEMPEL_SIZE - 1)];
                offset = (intptr_t)(src - *hp) & OFFSET_MASK;
                *hp = (uint16_t)(uintptr_t)src;
                cpy = src - offset;
                if (cpy >= (uchar_t *)s_start && cpy != src &&
                    src[0] == cpy[0] && src[1] == cpy[1] && src[2] == cpy[2]) {
                        *copymap |= copymask;
                        for (mlen = MATCH_MIN; mlen < MATCH_MAX; mlen++)
                                if (src[mlen] != cpy[mlen])
                                        break;
                        *dst++ = ((mlen - MATCH_MIN) << (NBBY - MATCH_BITS)) |
                            (offset >> NBBY);
                        *dst++ = (uchar_t)offset;
                        src += mlen;
                } else {
                        *dst++ = *src++;
                }
        }
        return (dst - (uchar_t *)d_start);
}

/*ARGSUSED*/
int
lzjb_decompress(void *s_start, void *d_start, size_t s_len, size_t d_len, int n)
{
        uchar_t *src = s_start;
        uchar_t *dst = d_start;
        uchar_t *d_end = (uchar_t *)d_start + d_len;
        uchar_t *cpy, copymap;
        int copymask = 1 << (NBBY - 1);

        while (dst < d_end) {
                if ((copymask <<= 1) == (1 << NBBY)) {
                        copymask = 1;
                        copymap = *src++;
                }
                if (copymap & copymask) {
                        int mlen = (src[0] >> (NBBY - MATCH_BITS)) + MATCH_MIN;
                        int offset = ((src[0] << NBBY) | src[1]) & OFFSET_MASK;
                        src += 2;
                        if ((cpy = dst - offset) < (uchar_t *)d_start)
                                return (-1);
                        while (--mlen >= 0 && dst < d_end)
                                *dst++ = *cpy++;
                } else {
                        *dst++ = *src++;
                }
        }
        return (0);
}