[linux.git] / fs / jffs2 / compr_rtime.c

/*
 * JFFS2 -- Journalling Flash File System, Version 2.
 *
 * Copyright © 2001-2007 Red Hat, Inc.
 * Copyright © 2004-2010 David Woodhouse <[email protected]>
 *
 * Created by Arjan van de Ven <[email protected]>
 *
 * 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)
{
	unsigned short positions[256];
	int outpos = 0;
	int pos=0;

	if (*dstlen <= 3)
		return -1;

	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)
{
	unsigned 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);
}
Commit	Line	Data
1da177e4 LT	1	/*
	2	* JFFS2 -- Journalling Flash File System, Version 2.
	3	*
c00c310e	4	* Copyright © 2001-2007 Red Hat, Inc.
6088c058	5	* Copyright © 2004-2010 David Woodhouse <[email protected]>
1da177e4 LT	6	*
	7	* Created by Arjan van de Ven <[email protected]>
	8	*
	9	* For licensing information, see the file 'LICENCE' in this directory.
	10	*
1da177e4 LT	11	*
	12	*
	13	* Very simple lz77-ish encoder.
	14	*
	15	* Theory of operation: Both encoder and decoder have a list of "last
	16	* occurrences" for every possible source-value; after sending the
	17	* first source-byte, the second byte indicated the "run" length of
	18	* matches
	19	*
	20	* The algorithm is intended to only send "whole bytes", no bit-messing.
	21	*
	22	*/
	23
	24	#include <linux/kernel.h>
	25	#include <linux/types.h>
	26	#include <linux/errno.h>
182ec4ee TG	27	#include <linux/string.h>
182ec4ee TG	28	#include <linux/jffs2.h>
1da177e4 LT	29	#include "compr.h"
	30
	31	/* _compress returns the compressed size, -1 if bigger */
	32	static int jffs2_rtime_compress(unsigned char *data_in,
	33	unsigned char *cpage_out,
088bd455	34	uint32_t sourcelen, uint32_t dstlen)
1da177e4	35	{
3367da56	36	unsigned short positions[256];
1da177e4 LT	37	int outpos = 0;
	38	int pos=0;
	39
90ada91f YY	40	if (*dstlen <= 3)
	41	return -1;
	42
182ec4ee TG	43	memset(positions,0,sizeof(positions));
182ec4ee TG	44
1da177e4 LT	45	while (pos < (sourcelen) && outpos <= (dstlen)-2) {
	46	int backpos, runlen=0;
	47	unsigned char value;
182ec4ee	48
1da177e4 LT	49	value = data_in[pos];
	50
	51	cpage_out[outpos++] = data_in[pos++];
182ec4ee	52
1da177e4 LT	53	backpos = positions[value];
1da177e4 LT	54	positions[value]=pos;
182ec4ee	55
1da177e4 LT	56	while ((backpos < pos) && (pos < (*sourcelen)) &&
	57	(data_in[pos]==data_in[backpos++]) && (runlen<255)) {
	58	pos++;
	59	runlen++;
	60	}
	61	cpage_out[outpos++] = runlen;
	62	}
	63
	64	if (outpos >= pos) {
	65	/* We failed */
	66	return -1;
	67	}
182ec4ee	68
1da177e4 LT	69	/* Tell the caller how much we managed to compress, and how much space it took */
	70	*sourcelen = pos;
	71	*dstlen = outpos;
	72	return 0;
182ec4ee	73	}
1da177e4 LT	74
	75
	76	static int jffs2_rtime_decompress(unsigned char *data_in,
	77	unsigned char *cpage_out,
088bd455	78	uint32_t srclen, uint32_t destlen)
1da177e4	79	{
3367da56	80	unsigned short positions[256];
1da177e4 LT	81	int outpos = 0;
1da177e4 LT	82	int pos=0;
182ec4ee TG	83
	84	memset(positions,0,sizeof(positions));
	85
1da177e4 LT	86	while (outpos<destlen) {
	87	unsigned char value;
	88	int backoffs;
	89	int repeat;
182ec4ee	90
1da177e4 LT	91	value = data_in[pos++];
	92	cpage_out[outpos++] = value; /* first the verbatim copied byte */
	93	repeat = data_in[pos++];
	94	backoffs = positions[value];
182ec4ee	95
1da177e4 LT	96	positions[value]=outpos;
	97	if (repeat) {
	98	if (backoffs + repeat >= outpos) {
	99	while(repeat) {
	100	cpage_out[outpos++] = cpage_out[backoffs++];
	101	repeat--;
	102	}
	103	} else {
	104	memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
182ec4ee	105	outpos+=repeat;
1da177e4 LT	106	}
	107	}
	108	}
ef53cb02	109	return 0;
182ec4ee	110	}
1da177e4 LT	111
	112	static struct jffs2_compressor jffs2_rtime_comp = {
	113	.priority = JFFS2_RTIME_PRIORITY,
	114	.name = "rtime",
	115	.compr = JFFS2_COMPR_RTIME,
	116	.compress = &jffs2_rtime_compress,
	117	.decompress = &jffs2_rtime_decompress,
	118	#ifdef JFFS2_RTIME_DISABLED
	119	.disabled = 1,
	120	#else
	121	.disabled = 0,
	122	#endif
	123	};
	124
	125	int jffs2_rtime_init(void)
	126	{
	127	return jffs2_register_compressor(&jffs2_rtime_comp);
	128	}
	129
	130	void jffs2_rtime_exit(void)
	131	{
	132	jffs2_unregister_compressor(&jffs2_rtime_comp);
	133	}