/* * JFFS2 -- Journalling Flash File System, Version 2. * * Copyright (C) 2001-2003 Red Hat, Inc. * * Created by Arjan van de Ven <arjanv@redhat.com> * * For licensing information, see the file 'LICENCE' in this directory. * * $Id: compr_rtime.c,v 1.14 2004/06/23 16:34:40 havasi Exp $ * * * 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 */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;}		   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);}