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260 lines
6.8 KiB
C
260 lines
6.8 KiB
C
/*
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* JFFS2 -- Journalling Flash File System, Version 2.
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*
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* Copyright (C) 2004 Patrik Kluba,
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* University of Szeged, Hungary
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*
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* For licensing information, see the file 'LICENCE' in the
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* jffs2 directory.
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*
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* $Id: compr_lzari.c,v 1.3 2004/06/23 16:34:39 havasi Exp $
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*
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*/
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/*
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Lempel-Ziv-Arithmetic coding compression module for jffs2
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Based on the LZARI source included in LDS (lossless datacompression sources)
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*/
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/* -*- Mode: C; indent-tabs-mode: t; c-basic-offset: 4; tab-width: 4 -*- */
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/*
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Original copyright follows:
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**************************************************************
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LZARI.C -- A Data Compression Program
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(tab = 4 spaces)
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**************************************************************
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4/7/1989 Haruhiko Okumura
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Use, distribute, and modify this program freely.
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Please send me your improved versions.
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PC-VAN SCIENCE
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NIFTY-Serve PAF01022
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CompuServe 74050,1022
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**************************************************************
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LZARI.C (c)1989 by Haruyasu Yoshizaki, Haruhiko Okumura, and Kenji Rikitake.
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All rights reserved. Permission granted for non-commercial use.
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*/
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/*
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2004-02-18 pajko <pajko(AT)halom(DOT)u-szeged(DOT)hu>
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Removed unused variables and fixed no return value
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2004-02-16 pajko <pajko(AT)halom(DOT)u-szeged(DOT)hu>
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Initial release
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*/
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#include <config.h>
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#include <linux/stddef.h>
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#include <jffs2/jffs2.h>
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#define N 4096 /* size of ring buffer */
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#define F 60 /* upper limit for match_length */
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#define THRESHOLD 2 /* encode string into position and length
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if match_length is greater than this */
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#define NIL N /* index for root of binary search trees */
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static unsigned char
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text_buf[N + F - 1]; /* ring buffer of size N,
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with extra F-1 bytes to facilitate string comparison */
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/********** Arithmetic Compression **********/
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/* If you are not familiar with arithmetic compression, you should read
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I. E. Witten, R. M. Neal, and J. G. Cleary,
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Communications of the ACM, Vol. 30, pp. 520-540 (1987),
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from which much have been borrowed. */
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#define M 15
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/* Q1 (= 2 to the M) must be sufficiently large, but not so
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large as the unsigned long 4 * Q1 * (Q1 - 1) overflows. */
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#define Q1 (1UL << M)
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#define Q2 (2 * Q1)
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#define Q3 (3 * Q1)
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#define Q4 (4 * Q1)
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#define MAX_CUM (Q1 - 1)
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#define N_CHAR (256 - THRESHOLD + F)
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/* character code = 0, 1, ..., N_CHAR - 1 */
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static unsigned long char_to_sym[N_CHAR], sym_to_char[N_CHAR + 1];
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static unsigned long
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sym_freq[N_CHAR + 1], /* frequency for symbols */
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sym_cum[N_CHAR + 1], /* cumulative freq for symbols */
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position_cum[N + 1]; /* cumulative freq for positions */
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static void StartModel(void) /* Initialize model */
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{
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unsigned long ch, sym, i;
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sym_cum[N_CHAR] = 0;
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for (sym = N_CHAR; sym >= 1; sym--) {
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ch = sym - 1;
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char_to_sym[ch] = sym; sym_to_char[sym] = ch;
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sym_freq[sym] = 1;
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sym_cum[sym - 1] = sym_cum[sym] + sym_freq[sym];
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}
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sym_freq[0] = 0; /* sentinel (!= sym_freq[1]) */
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position_cum[N] = 0;
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for (i = N; i >= 1; i--)
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position_cum[i - 1] = position_cum[i] + 10000 / (i + 200);
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/* empirical distribution function (quite tentative) */
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/* Please devise a better mechanism! */
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}
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static void UpdateModel(unsigned long sym)
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{
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unsigned long c, ch_i, ch_sym;
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unsigned long i;
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if (sym_cum[0] >= MAX_CUM) {
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c = 0;
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for (i = N_CHAR; i > 0; i--) {
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sym_cum[i] = c;
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c += (sym_freq[i] = (sym_freq[i] + 1) >> 1);
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}
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sym_cum[0] = c;
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}
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for (i = sym; sym_freq[i] == sym_freq[i - 1]; i--) ;
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if (i < sym) {
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ch_i = sym_to_char[i]; ch_sym = sym_to_char[sym];
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sym_to_char[i] = ch_sym; sym_to_char[sym] = ch_i;
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char_to_sym[ch_i] = sym; char_to_sym[ch_sym] = i;
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}
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sym_freq[i]++;
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while (--i > 0) sym_cum[i]++;
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sym_cum[0]++;
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}
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static unsigned long BinarySearchSym(unsigned long x)
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/* 1 if x >= sym_cum[1],
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N_CHAR if sym_cum[N_CHAR] > x,
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i such that sym_cum[i - 1] > x >= sym_cum[i] otherwise */
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{
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unsigned long i, j, k;
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i = 1; j = N_CHAR;
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while (i < j) {
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k = (i + j) / 2;
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if (sym_cum[k] > x) i = k + 1; else j = k;
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}
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return i;
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}
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unsigned long BinarySearchPos(unsigned long x)
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/* 0 if x >= position_cum[1],
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N - 1 if position_cum[N] > x,
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i such that position_cum[i] > x >= position_cum[i + 1] otherwise */
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{
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unsigned long i, j, k;
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i = 1; j = N;
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while (i < j) {
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k = (i + j) / 2;
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if (position_cum[k] > x) i = k + 1; else j = k;
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}
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return i - 1;
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}
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static int Decode(unsigned char *srcbuf, unsigned char *dstbuf, unsigned long srclen,
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unsigned long dstlen) /* Just the reverse of Encode(). */
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{
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unsigned long i, r, j, k, c, range, sym;
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unsigned char *ip, *op;
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unsigned char *srcend = srcbuf + srclen;
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unsigned char *dstend = dstbuf + dstlen;
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unsigned char buffer = 0;
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unsigned char mask = 0;
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unsigned long low = 0;
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unsigned long high = Q4;
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unsigned long value = 0;
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ip = srcbuf;
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op = dstbuf;
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for (i = 0; i < M + 2; i++) {
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value *= 2;
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if ((mask >>= 1) == 0) {
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buffer = (ip >= srcend) ? 0 : *(ip++);
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mask = 128;
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}
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value += ((buffer & mask) != 0);
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}
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StartModel();
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for (i = 0; i < N - F; i++) text_buf[i] = ' ';
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r = N - F;
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while (op < dstend) {
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range = high - low;
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sym = BinarySearchSym((unsigned long)
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(((value - low + 1) * sym_cum[0] - 1) / range));
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high = low + (range * sym_cum[sym - 1]) / sym_cum[0];
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low += (range * sym_cum[sym ]) / sym_cum[0];
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for ( ; ; ) {
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if (low >= Q2) {
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value -= Q2; low -= Q2; high -= Q2;
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} else if (low >= Q1 && high <= Q3) {
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value -= Q1; low -= Q1; high -= Q1;
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} else if (high > Q2) break;
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low += low; high += high;
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value *= 2;
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if ((mask >>= 1) == 0) {
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buffer = (ip >= srcend) ? 0 : *(ip++);
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mask = 128;
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}
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value += ((buffer & mask) != 0);
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}
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c = sym_to_char[sym];
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UpdateModel(sym);
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if (c < 256) {
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if (op >= dstend) return -1;
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*(op++) = c;
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text_buf[r++] = c;
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r &= (N - 1);
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} else {
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j = c - 255 + THRESHOLD;
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range = high - low;
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i = BinarySearchPos((unsigned long)
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(((value - low + 1) * position_cum[0] - 1) / range));
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high = low + (range * position_cum[i ]) / position_cum[0];
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low += (range * position_cum[i + 1]) / position_cum[0];
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for ( ; ; ) {
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if (low >= Q2) {
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value -= Q2; low -= Q2; high -= Q2;
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} else if (low >= Q1 && high <= Q3) {
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value -= Q1; low -= Q1; high -= Q1;
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} else if (high > Q2) break;
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low += low; high += high;
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value *= 2;
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if ((mask >>= 1) == 0) {
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buffer = (ip >= srcend) ? 0 : *(ip++);
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mask = 128;
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}
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value += ((buffer & mask) != 0);
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}
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i = (r - i - 1) & (N - 1);
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for (k = 0; k < j; k++) {
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c = text_buf[(i + k) & (N - 1)];
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if (op >= dstend) return -1;
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*(op++) = c;
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text_buf[r++] = c;
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r &= (N - 1);
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}
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}
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}
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return 0;
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}
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int lzari_decompress(unsigned char *data_in, unsigned char *cpage_out,
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u32 srclen, u32 destlen)
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{
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return Decode(data_in, cpage_out, srclen, destlen);
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}
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