/*
   * JFFS2 -- Journalling Flash File System, Version 2.
   *

   * Copyright © 2001-2007 Red Hat, Inc.

   * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>

   *
   * 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)

  {

  	unsigned 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)

  {

  	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);
  }