lzss.c

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/* Credits for lzss go to Haruhiko Okumura */

#include <stdio.h>
#include <stdlib.h>

/* #include <string.h>
#include <ctype.h> */

#include "globals.h"


void InitTree(void)  /* initialize trees */
{
	int  i;
	/* For i = 0 to N - 1, rson[i] and lson[i] will be the right and
	   left children of node i.  These nodes need not be initialized.
	   Also, dad[i] is the parent of node i.  These are initialized to
	   NIL (= N), which stands for 'not used.'
	   For i = 0 to 255, rson[N + i + 1] is the root of the tree
	   for strings that begin with character i.  These are initialized
	   to NIL.  Note there are 256 trees. */
	for (i = N + 1; i <= N + 256; i++) rson[i] = NIL;
	for (i = 0; i < N; i++) dad[i] = NIL;
}

void InsertNode(int r)
	/* Inserts string of length F, text_buf[r..r+F_SS-1], into one of the
	   trees (text_buf[r]'th tree) and returns the longest-match position
	   and length via the global variables match_position and match_length.
	   If match_length = F_SS, then removes the old node in favor of the new
	   one, because the old one will be deleted sooner.
	   Note r plays double role, as tree node and position in buffer. */
{
	int  i, p, cmp;
	unsigned char  *key;

	cmp = 1;  key = &text_buf[r];  p = N + 1 + key[0];
	rson[r] = lson[r] = NIL;  match_length = 0;
	for ( ; ; ) {
		if (cmp >= 0) {
			if (rson[p] != NIL) p = rson[p];
			else {  rson[p] = r;  dad[r] = p;  return;  }
		} else {
			if (lson[p] != NIL) p = lson[p];
			else {  lson[p] = r;  dad[r] = p;  return;  }
		}
		for (i = 1; i < F_SS; i++)
			if ((cmp = key[i] - text_buf[p + i]) != 0)  break;
		if (i > match_length) {
			match_position = p;
			if ((match_length = i) >= F_SS)  break;
		}
	}
	dad[r] = dad[p];  lson[r] = lson[p];  rson[r] = rson[p];
	dad[lson[p]] = r;  dad[rson[p]] = r;
	if (rson[dad[p]] == p) rson[dad[p]] = r;
	else                   lson[dad[p]] = r;
	dad[p] = NIL;  /* remove p */
}

void DeleteNode(int p)  /* deletes node p from tree */
{
	int  q;
	if (dad[p] == NIL) return;  /* not in tree */
	if (rson[p] == NIL) q = lson[p];
	else if (lson[p] == NIL) q = rson[p];
	else {
		q = lson[p];
		if (rson[q] != NIL) {
			do {  q = rson[q];  } while (rson[q] != NIL);
			rson[dad[q]] = lson[q];  dad[lson[q]] = dad[q];
			lson[q] = lson[p];  dad[lson[p]] = q;
		}
		rson[q] = rson[p];  dad[rson[p]] = q;
	}
	dad[q] = dad[p];
	if (rson[dad[p]] == p) rson[dad[p]] = q;  else lson[dad[p]] = q;
	dad[p] = NIL;
}

void Encode(void)
{
	int  i, c, len, r, s, last_match_length, code_buf_ptr;
	unsigned char  code_buf[17], mask;

	InitTree();  /* initialize trees */
	code_buf[0] = 0;  /* code_buf[1..16] saves eight units of code, and
		code_buf[0] works as eight flags, "1" representing that the unit
		is an unencoded letter (1 byte), "0" a position-and-length pair
		(2 bytes).  Thus, eight units require at most 16 bytes of code. */
	code_buf_ptr = mask = 1;
	s = 0;  r = N - F_SS;
	for (i = s; i < r; i++) text_buf[i] = ' ';  /* Clear the buffer with
		any character that will appear often. */
	for (len = 0; len < F_SS && (c = getc_buffer()) != EOF; len++)
		text_buf[r + len] = c;  /* Read F_SS bytes into the last F_SS bytes of
			the buffer */
	if ((textsize = len) == 0) return;  /* text of size zero */
	for (i = 1; i <= F_SS; i++) InsertNode(r - i);  /* Insert the F_SS strings,
		each of which begins with one or more 'space' characters.  Note
		the order in which these strings are inserted.  This way,
		degenerate trees will be less likely to occur. */
	InsertNode(r);  /* Finally, insert the whole string just read.  The
		global variables match_length and match_position are set. */
	do {
		if (match_length > len) match_length = len;  /* match_length
			may be spuriously long near the end of text. */
		if (match_length <= THRESHOLD) {
			match_length = 1;  /* Not long enough match.  Send one byte. */
			code_buf[0] |= mask;  /* 'send one byte' flag */
			code_buf[code_buf_ptr++] = text_buf[r];  /* Send uncoded. */
		} else {
			code_buf[code_buf_ptr++] = (unsigned char) match_position;
			code_buf[code_buf_ptr++] = (unsigned char)
				(((match_position >> 4) & 0xf0)
			  | (match_length - (THRESHOLD + 1)));  /* Send position and
					length pair. Note match_length > THRESHOLD. */
		}
		if ((mask <<= 1) == 0) {  /* Shift mask left one bit. */
			for (i = 0; i < code_buf_ptr; i++)  /* Send at most 8 units of */
				putc_buffer(code_buf[i]);     /* code together */
			codesize += code_buf_ptr;
			code_buf[0] = 0;  code_buf_ptr = mask = 1;
		}
		last_match_length = match_length;
		for (i = 0; i < last_match_length &&
				(c = getc_buffer()) != EOF; i++) {
			DeleteNode(s);		/* Delete old strings and */
			text_buf[s] = c;	/* read new bytes */
			if (s < F_SS - 1) text_buf[s + N] = c;  /* If the position is
				near the end of buffer, extend the buffer to make
				string comparison easier. */
			s = (s + 1) & (N - 1);  r = (r + 1) & (N - 1);
				/* Since this is a ring buffer, increment the position
				   modulo N. */
			InsertNode(r);	/* Register the string in text_buf[r..r+F_SS-1] */
		}
		if ((textsize += i) > printcount) {
			printf("%12ld\r", textsize);  printcount += 1024;
				/* Reports progress each time the textsize exceeds
				   multiples of 1024. */
		}
		while (i++ < last_match_length) {	/* After the end of text, */
			DeleteNode(s);					/* no need to read, but */
			s = (s + 1) & (N - 1);  r = (r + 1) & (N - 1);
			if (--len) InsertNode(r);		/* buffer may not be empty. */
		}
	} while (len > 0);	/* until length of string to be processed is zero */
	if (code_buf_ptr > 1) {		/* Send remaining code. */
		for (i = 0; i < code_buf_ptr; i++) putc_buffer(code_buf[i]);
		codesize += code_buf_ptr;
	}
	printf("original data: %ld bytes\n", textsize);	/* Encoding is done. */
	printf("compressed data: %ld bytes\n", codesize);
}

void Decode(void)	/* Just the reverse of Encode(). */
{
	int  i, j, k, r, c;
	unsigned int  flags;

	for (i = 0; i < N - F_SS; i++) text_buf[i] = ' ';
	r = N - F_SS;  flags = 0;
	for ( ; ; ) {
		if (((flags >>= 1) & 256) == 0) {
			if ((c = getc_buffer()) == EOF) break;
			flags = c | 0xff00;		/* uses higher byte cleverly */
		}							/* to count eight */
		if (flags & 1) {
			if ((c = getc_buffer()) == EOF) break;
			putc_buffer(c);  text_buf[r++] = c;  r &= (N - 1);
		} else {
			if ((i = getc_buffer()) == EOF) break;
			if ((j = getc_buffer()) == EOF) break;
			i |= ((j & 0xf0) << 4);  j = (j & 0x0f) + THRESHOLD;
			for (k = 0; k <= j; k++) {
				c = text_buf[(i + k) & (N - 1)];
				putc_buffer(c);  text_buf[r++] = c;  r &= (N - 1);
			}
		}
	}
}

long lzss_compress(unsigned char* tbuffer, unsigned char* fbuffer, long real_size)
{
  lz_init();
  from_buffer = fbuffer;
  to_buffer = tbuffer;
  from_max = real_size;
  Encode();
  return(codesize);
}

void lzss_decompress(unsigned char* fbuffer, unsigned char* tbuffer, long comp_size)
{
  lz_init();
  from_buffer = fbuffer;
  from_max = comp_size;
  to_buffer = tbuffer;
  Decode();
  return;
}