
/*
 *     xDMS  v1.3  -  Portable DMS archive unpacker  -  Public Domain
 *     Written by     Andre Rodrigues de la Rocha  <adlroc@usa.net>
 *
 *     Lempel-Ziv-DynamicHuffman decompression functions used in Deep
 *     mode.
 *     Most routines ripped from LZHUF written by  Haruyasu Yoshizaki
 *
 */

#include <string.h>

#include "cdata.h"
#include "tables.h"
#include "u_deep.h"
#include "getbits.h"


static USHORT DecodeChar(void);
static USHORT DecodePosition(void);
static void update(USHORT c);
static void reconst(void);


USHORT deep_text_loc;
int init_deep_tabs=1;



#define DBITMASK 0x3fff   /*  uses 16Kb dictionary  */

#define F       60  /* lookahead buffer size */
#define THRESHOLD   2
#define N_CHAR      (256 - THRESHOLD + F)   /* kinds of characters (character code = 0..N_CHAR-1) */
#define T       (N_CHAR * 2 - 1)    /* size of table */
#define R       (T - 1)         /* position of root */
#define MAX_FREQ    0x8000      /* updates tree when the */


static USHORT freq[T + 1]; /* frequency table */

static USHORT prnt[T + N_CHAR]; /* pointers to parent nodes, except for the */
				/* elements [T..T + N_CHAR - 1] which are used to get */
				/* the positions of leaves corresponding to the codes. */

static USHORT son[T];   /* pointers to child nodes (son[], son[] + 1) */



void Init_DEEP_Tabs(void){
	USHORT i, j;

	for (i = 0; i < N_CHAR; i++) {
		freq[i] = 1;
		son[i] = (USHORT)(i + T);
		prnt[i + T] = i;
	}
	i = 0; j = N_CHAR;
	while (j <= R) {
		freq[j] = (USHORT) (freq[i] + freq[i + 1]);
		son[j] = i;
		prnt[i] = prnt[i + 1] = j;
		i += 2; j++;
	}
	freq[T] = 0xffff;
	prnt[R] = 0;

	init_deep_tabs = 0;
}



USHORT Unpack_DEEP(UCHAR *in, UCHAR *out, USHORT origsize){
	USHORT i, j, c;
	UCHAR *outend;

	initbitbuf(in);

	if (init_deep_tabs) Init_DEEP_Tabs();

	outend = out+origsize;
	while (out < outend) {
		c = DecodeChar();
		if (c < 256) {
			*out++ = text[deep_text_loc++ & DBITMASK] = (UCHAR)c;
		} else {
			j = (USHORT) (c - 255 + THRESHOLD);
			i = (USHORT) (deep_text_loc - DecodePosition() - 1);
			while (j--) *out++ = text[deep_text_loc++ & DBITMASK] = text[i++ & DBITMASK];
		}
	}

	deep_text_loc = (USHORT)((deep_text_loc+60) & DBITMASK);

	return 0;
}



static USHORT DecodeChar(void){
	USHORT c;

	c = son[R];

	/* travel from root to leaf, */
	/* choosing the smaller child node (son[]) if the read bit is 0, */
	/* the bigger (son[]+1} if 1 */
	while (c < T) {
		c = son[c + GETBITS(1)];
		DROPBITS(1);
	}
	c -= T;
	update(c);
	return c;
}



static USHORT DecodePosition(void){
	USHORT i, j, c;

	i = GETBITS(8);  DROPBITS(8);
	c = (USHORT) (d_code[i] << 8);
	j = d_len[i];
	i = (USHORT) (((i << j) | GETBITS(j)) & 0xff);  DROPBITS(j);

	return (USHORT) (c | i) ;
}



/* reconstruction of tree */

static void reconst(void){
	USHORT i, j, k, f, l;

	/* collect leaf nodes in the first half of the table */
	/* and replace the freq by (freq + 1) / 2. */
	j = 0;
	for (i = 0; i < T; i++) {
		if (son[i] >= T) {
			freq[j] = (USHORT) ((freq[i] + 1) / 2);
			son[j] = son[i];
			j++;
		}
	}
	/* begin constructing tree by connecting sons */
	for (i = 0, j = N_CHAR; j < T; i += 2, j++) {
		k = (USHORT) (i + 1);
		f = freq[j] = (USHORT) (freq[i] + freq[k]);
		for (k = (USHORT)(j - 1); f < freq[k]; k--);
		k++;
		l = (USHORT)((j - k) * 2);
		memmove(&freq[k + 1], &freq[k], (size_t)l);
		freq[k] = f;
		memmove(&son[k + 1], &son[k], (size_t)l);
		son[k] = i;
	}
	/* connect prnt */
	for (i = 0; i < T; i++) {
		if ((k = son[i]) >= T) {
			prnt[k] = i;
		} else {
			prnt[k] = prnt[k + 1] = i;
		}
	}
}



/* increment frequency of given code by one, and update tree */

static void update(USHORT c){
	USHORT i, j, k, l;

	if (freq[R] == MAX_FREQ) {
		reconst();
	}
	c = prnt[c + T];
	do {
		k = ++freq[c];

		/* if the order is disturbed, exchange nodes */
		if (k > freq[l = (USHORT)(c + 1)]) {
			while (k > freq[++l]);
			l--;
			freq[c] = freq[l];
			freq[l] = k;

			i = son[c];
			prnt[i] = l;
			if (i < T) prnt[i + 1] = l;

			j = son[l];
			son[l] = i;

			prnt[j] = c;
			if (j < T) prnt[j + 1] = c;
			son[c] = j;

			c = l;
		}
	} while ((c = prnt[c]) != 0); /* repeat up to root */
}


