compr_rtime.c
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/*
* JFFS2 -- Journalling Flash File System, Version 2.
*
* Copyright © 2001-2007 Red Hat, Inc.
*
* Created by Arjan van de Ven <arjanv@redhat.com>
*
* For licensing information, see the file 'LICENCE' in this directory.
*
*
*
* Very simple lz77-ish encoder.
*
* Theory of operation: Both encoder and decoder have a list of "last
* occurrences" for every possible source-value; after sending the
* first source-byte, the second byte indicated the "run" length of
* matches
*
* The algorithm is intended to only send "whole bytes", no bit-messing.
*
*/
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/jffs2.h>
#include "compr.h"
/* _compress returns the compressed size, -1 if bigger */
static int jffs2_rtime_compress(unsigned char *data_in,
unsigned char *cpage_out,
uint32_t *sourcelen, uint32_t *dstlen,
void *model)
{
short positions[256];
int outpos = 0;
int pos=0;
memset(positions,0,sizeof(positions));
while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
int backpos, runlen=0;
unsigned char value;
value = data_in[pos];
cpage_out[outpos++] = data_in[pos++];
backpos = positions[value];
positions[value]=pos;
while ((backpos < pos) && (pos < (*sourcelen)) &&
(data_in[pos]==data_in[backpos++]) && (runlen<255)) {
pos++;
runlen++;
}
cpage_out[outpos++] = runlen;
}
if (outpos >= pos) {
/* We failed */
return -1;
}
/* Tell the caller how much we managed to compress, and how much space it took */
*sourcelen = pos;
*dstlen = outpos;
return 0;
}
static int jffs2_rtime_decompress(unsigned char *data_in,
unsigned char *cpage_out,
uint32_t srclen, uint32_t destlen,
void *model)
{
short positions[256];
int outpos = 0;
int pos=0;
memset(positions,0,sizeof(positions));
while (outpos<destlen) {
unsigned char value;
int backoffs;
int repeat;
value = data_in[pos++];
cpage_out[outpos++] = value; /* first the verbatim copied byte */
repeat = data_in[pos++];
backoffs = positions[value];
positions[value]=outpos;
if (repeat) {
if (backoffs + repeat >= outpos) {
while(repeat) {
cpage_out[outpos++] = cpage_out[backoffs++];
repeat--;
}
} else {
memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
outpos+=repeat;
}
}
}
return 0;
}
static struct jffs2_compressor jffs2_rtime_comp = {
.priority = JFFS2_RTIME_PRIORITY,
.name = "rtime",
.compr = JFFS2_COMPR_RTIME,
.compress = &jffs2_rtime_compress,
.decompress = &jffs2_rtime_decompress,
#ifdef JFFS2_RTIME_DISABLED
.disabled = 1,
#else
.disabled = 0,
#endif
};
int jffs2_rtime_init(void)
{
return jffs2_register_compressor(&jffs2_rtime_comp);
}
void jffs2_rtime_exit(void)
{
jffs2_unregister_compressor(&jffs2_rtime_comp);
}