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LZC.C
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1995-03-05
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/**************************************************************
LZARI.C -- A Data Compression Program
(tab = 4 spaces)
***************************************************************
4/7/1989 Haruhiko Okumura
Use, distribute, and modify this program freely.
Please send me your improved versions.
PC-VAN SCIENCE
NIFTY-Serve PAF01022
CompuServe 74050,1022
**************************************************************/
/****************************************************************************/
/* LZC compression system */
/* Functions under DOS4Gw and PmodeW */
/*--------------------------------------------------------------------------*/
/* Modified by Kodiak of The Apollo Project */
/* AKA Charles Jones */
/* 1122 s 32nd St #2 */
/* Omaha, NE 68105 */
/* (402)-346-8974 */
/* */
/* Email: CAD@UnOmaha.edu */
/* IRC : #Coders */
/* */
/****************************************************************************/
/* I take no credit for this compresion system. I simply modifed the */
/* original code supplied by Haruhiko Okumura. This code only DECODES */
/* from either disk files or memory. I included this system to show how */
/* easy compression is to add to your projects. */
/****************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
extern FILE *kadfile;
unsigned char *targetarray;
long int targetpointer;
/********** Bit I/O **********/
unsigned long int textsize = 0, printcount = 0;
/********** LZSS with multiple binary trees **********/
#define N 4096 /* size of ring buffer */
#define F 60 /* upper limit for match_length */
#define THRESHOLD 2 /* encode string into position and length
if match_length is greater than this */
unsigned char text_buf[N + F - 1]; /* ring buffer of size N,
with extra F-1 bytes to facilitate string comparison */
/********** Arithmetic Compression **********/
/* If you are not familiar with arithmetic compression, you should read
I. E. Witten, R. M. Neal, and J. G. Cleary,
Communications of the ACM, Vol. 30, pp. 520-540 (1987),
from which much have been borrowed. */
#define M 15
/* Q1 (= 2 to the M) must be sufficiently large, but not so
large as the unsigned long 4 * Q1 * (Q1 - 1) overflows. */
#define Q1 (1UL << M)
#define Q2 (2 * Q1)
#define Q3 (3 * Q1)
#define Q4 (4 * Q1)
#define MAX_CUM (Q1 - 1)
#define N_CHAR (256 - THRESHOLD + F)
/* character code = 0, 1, ..., N_CHAR - 1 */
unsigned long int low = 0, high = Q4, value = 0;
int shifts = 0; /* counts for magnifying low and high around Q2 */
int char_to_sym[N_CHAR], sym_to_char[N_CHAR + 1];
unsigned int
sym_freq[N_CHAR + 1], /* frequency for symbols */
sym_cum[N_CHAR + 1], /* cumulative freq for symbols */
position_cum[N + 1]; /* cumulative freq for positions */
char *sourcearray;
long int sourcepointer;
int (*getinputchar)(FILE *filename); /* pointer to primary irq */
void putcs(unsigned char c)
{
targetarray[targetpointer++] = c;
}
int getcs(FILE *filename)
{
char c;
c = sourcearray[sourcepointer++];
return(c);
}
int GetBit(void) /* Get one bit (0 or 1) */
{
static unsigned int buffer, mask = 0;
if ((mask >>= 1) == 0) {
buffer = getinputchar(kadfile); mask = 128;
}
return ((buffer & mask) != 0);
}
void StartModel(void) /* Initialize model */
{
int ch, sym, i;
sym_cum[N_CHAR] = 0;
for (sym = N_CHAR; sym >= 1; sym--) {
ch = sym - 1;
char_to_sym[ch] = sym; sym_to_char[sym] = ch;
sym_freq[sym] = 1;
sym_cum[sym - 1] = sym_cum[sym] + sym_freq[sym];
}
sym_freq[0] = 0; /* sentinel (!= sym_freq[1]) */
position_cum[N] = 0;
for (i = N; i >= 1; i--)
position_cum[i - 1] = position_cum[i] + 10000 / (i + 200);
/* empirical distribution function (quite tentative) */
/* Please devise a better mechanism! */
}
void UpdateModel(int sym)
{
int i, c, ch_i, ch_sym;
if (sym_cum[0] >= MAX_CUM) {
c = 0;
for (i = N_CHAR; i > 0; i--) {
sym_cum[i] = c;
c += (sym_freq[i] = (sym_freq[i] + 1) >> 1);
}
sym_cum[0] = c;
}
for (i = sym; sym_freq[i] == sym_freq[i - 1]; i--) ;
if (i < sym) {
ch_i = sym_to_char[i]; ch_sym = sym_to_char[sym];
sym_to_char[i] = ch_sym; sym_to_char[sym] = ch_i;
char_to_sym[ch_i] = sym; char_to_sym[ch_sym] = i;
}
sym_freq[i]++;
while (--i >= 0) sym_cum[i]++;
}
int BinarySearchSym(unsigned int x)
/* 1 if x >= sym_cum[1],
N_CHAR if sym_cum[N_CHAR] > x,
i such that sym_cum[i - 1] > x >= sym_cum[i] otherwise */
{
int i, j, k;
i = 1; j = N_CHAR;
while (i < j) {
k = (i + j) / 2;
if (sym_cum[k] > x) i = k + 1; else j = k;
}
return i;
}
int BinarySearchPos(unsigned int x)
/* 0 if x >= position_cum[1],
N - 1 if position_cum[N] > x,
i such that position_cum[i] > x >= position_cum[i + 1] otherwise */
{
int i, j, k;
i = 1; j = N;
while (i < j) {
k = (i + j) / 2;
if (position_cum[k] > x) i = k + 1; else j = k;
}
return i - 1;
}
void StartDecode(void)
{
int i;
for (i = 0; i < M + 2; i++)
value = 2 * value + GetBit();
}
int DecodeChar(void)
{
int sym, ch;
unsigned long int range;
range = high - low;
sym = BinarySearchSym((unsigned int)
(((value - low + 1) * sym_cum[0] - 1) / range));
high = low + (range * sym_cum[sym - 1]) / sym_cum[0];
low += (range * sym_cum[sym ]) / sym_cum[0];
for ( ; ; ) {
if (low >= Q2) {
value -= Q2; low -= Q2; high -= Q2;
} else if (low >= Q1 && high <= Q3) {
value -= Q1; low -= Q1; high -= Q1;
} else if (high > Q2) break;
low += low; high += high;
value = 2 * value + GetBit();
}
ch = sym_to_char[sym];
UpdateModel(sym);
return ch;
}
int DecodePosition(void)
{
int position;
unsigned long int range;
range = high - low;
position = BinarySearchPos((unsigned int)
(((value - low + 1) * position_cum[0] - 1) / range));
high = low + (range * position_cum[position ]) / position_cum[0];
low += (range * position_cum[position + 1]) / position_cum[0];
for ( ; ; ) {
if (low >= Q2) {
value -= Q2; low -= Q2; high -= Q2;
} else if (low >= Q1 && high <= Q3) {
value -= Q1; low -= Q1; high -= Q1;
} else if (high > Q2) break;
low += low; high += high;
value = 2 * value + GetBit();
}
return position;
}
/********** Encode and Decode **********/
int Decode(void)
{
int i, j, k, r, c;
unsigned long int count;
if (fread(&textsize, sizeof textsize, 1, kadfile) != 1)
return(8);
if (sourcearray != NULL)
fread(sourcearray, textsize, 1, kadfile);
if (textsize == 0) return(7);
StartDecode(); StartModel();
for (i = 0; i < N - F; i++) text_buf[i] = ' ';
r = N - F;
for (count = 0; count < textsize; ) {
c = DecodeChar();
if (c < 256) {
putcs(c); text_buf[r++] = c;
r &= (N - 1); count++;
} else {
i = (r - DecodePosition() - 1) & (N - 1);
j = c - 255 + THRESHOLD;
for (k = 0; k < j; k++) {
c = text_buf[(i + k) & (N - 1)];
putcs(c); text_buf[r++] = c;
r &= (N - 1); count++;
}
}
}
return(0);
}
int decompress(unsigned char *where, int filesize)
{
int temp;
sourcepointer = 0;
sourcearray = (char *) malloc(filesize);
getinputchar = getc;
if (sourcearray != NULL)
getinputchar = getcs;
targetarray = where;
targetpointer = 0;
temp = Decode();
free ((void *) sourcearray);
return(temp);
}