cnq3/code/qcommon/huffman.cpp

/*
===========================================================================
Copyright (C) 1999-2005 Id Software, Inc.

This file is part of Quake III Arena source code.

Quake III Arena source code is free software; you can redistribute it
and/or modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of the License,
or (at your option) any later version.

Quake III Arena source code is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with Quake III Arena source code; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
===========================================================================
*/

/* This is based on the Adaptive Huffman algorithm described in Sayood's Data
 * Compression book.  The ranks are not actually stored, but implicitly defined
 * by the location of a node within a doubly-linked list */

#include "q_shared.h"
#include "qcommon.h"

#define HMAX			256		/* Maximum symbol */
#define NYT				HMAX	/* NYT = Not Yet Transmitted */
#define INTERNAL_NODE	(HMAX+1)

static int			bloc = 0;

typedef struct nodetype {
    struct    nodetype *left, *right, *parent; /* tree structure */
    struct    nodetype *next, *prev; /* doubly-linked list */
    struct    nodetype **head; /* highest ranked node in block */
    int        weight;
    int        symbol;
} node_t;

typedef struct {
    int            blocNode;
    int            blocPtrs;

    node_t*        tree;
    node_t*        lhead;
    node_t*        ltail;
    node_t*        loc[HMAX + 1];
    node_t**       freelist;

    node_t         nodeList[768];
    node_t*        nodePtrs[768];
} huff_t;

typedef struct {
    huff_t        compressor;
    huff_t        decompressor;
} huffman_t;


/* Add a bit to the output file (buffered) */
static void add_bit(char bit, byte *fout) {
	if ((bloc&7) == 0) {
		fout[(bloc>>3)] = 0;
	}
	fout[(bloc>>3)] |= bit << (bloc&7);
	bloc++;
}


/* Receive one bit from the input file (buffered) */
static int get_bit(byte *fin) {
	int t;
	t = (fin[(bloc>>3)] >> (bloc&7)) & 0x1;
	bloc++;
	return t;
}


static node_t **get_ppnode(huff_t* huff) {
	node_t **tppnode;
	if (!huff->freelist) {
		return &(huff->nodePtrs[huff->blocPtrs++]);
	} else {
		tppnode = huff->freelist;
		huff->freelist = (node_t **)*tppnode;
		return tppnode;
	}
}


static void free_ppnode(huff_t* huff, node_t **ppnode) {
	*ppnode = (node_t *)huff->freelist;
	huff->freelist = ppnode;
}


/* Swap the location of these two nodes in the tree */
static void swap(huff_t* huff, node_t *node1, node_t *node2) { 
	node_t *par1, *par2;

	par1 = node1->parent;
	par2 = node2->parent;

	if (par1) {
		if (par1->left == node1) {
			par1->left = node2;
		} else {
	      par1->right = node2;
		}
	} else {
		huff->tree = node2;
	}

	if (par2) {
		if (par2->left == node2) {
			par2->left = node1;
		} else {
			par2->right = node1;
		}
	} else {
		huff->tree = node1;
	}
  
	node1->parent = par2;
	node2->parent = par1;
}


/* Swap these two nodes in the linked list (update ranks) */
static void swaplist(node_t *node1, node_t *node2) {
	node_t *par1;

	par1 = node1->next;
	node1->next = node2->next;
	node2->next = par1;

	par1 = node1->prev;
	node1->prev = node2->prev;
	node2->prev = par1;

	if (node1->next == node1) {
		node1->next = node2;
	}
	if (node2->next == node2) {
		node2->next = node1;
	}
	if (node1->next) {
		node1->next->prev = node1;
	}
	if (node2->next) {
		node2->next->prev = node2;
	}
	if (node1->prev) {
		node1->prev->next = node1;
	}
	if (node2->prev) {
		node2->prev->next = node2;
	}
}


/* Do the increments */
static void increment(huff_t* huff, node_t *node) {
	node_t *lnode;

	if (!node) {
		return;
	}

	if (node->next != NULL && node->next->weight == node->weight) {
	    lnode = *node->head;
		if (lnode != node->parent) {
			swap(huff, lnode, node);
		}
		swaplist(lnode, node);
	}
	if (node->prev && node->prev->weight == node->weight) {
		*node->head = node->prev;
	} else {
	    *node->head = NULL;
		free_ppnode(huff, node->head);
	}
	node->weight++;
	if (node->next && node->next->weight == node->weight) {
		node->head = node->next->head;
	} else { 
		node->head = get_ppnode(huff);
		*node->head = node;
	}
	if (node->parent) {
		increment(huff, node->parent);
		if (node->prev == node->parent) {
			swaplist(node, node->parent);
			if (*node->head == node) {
				*node->head = node->parent;
			}
		}
	}
}


static void Huff_addRef(huff_t* huff, byte ch) {
	node_t *tnode, *tnode2;
	if (huff->loc[ch] == NULL) { /* if this is the first transmission of this node */
		tnode = &(huff->nodeList[huff->blocNode++]);
		tnode2 = &(huff->nodeList[huff->blocNode++]);

		tnode2->symbol = INTERNAL_NODE;
		tnode2->weight = 1;
		tnode2->next = huff->lhead->next;
		if (huff->lhead->next) {
			huff->lhead->next->prev = tnode2;
			if (huff->lhead->next->weight == 1) {
				tnode2->head = huff->lhead->next->head;
			} else {
				tnode2->head = get_ppnode(huff);
				*tnode2->head = tnode2;
			}
		} else {
			tnode2->head = get_ppnode(huff);
			*tnode2->head = tnode2;
		}
		huff->lhead->next = tnode2;
		tnode2->prev = huff->lhead;
 
		tnode->symbol = ch;
		tnode->weight = 1;
		tnode->next = huff->lhead->next;
		if (huff->lhead->next) {
			huff->lhead->next->prev = tnode;
			if (huff->lhead->next->weight == 1) {
				tnode->head = huff->lhead->next->head;
			} else {
				/* this should never happen */
				tnode->head = get_ppnode(huff);
				*tnode->head = tnode2;
		    }
		} else {
			/* this should never happen */
			tnode->head = get_ppnode(huff);
			*tnode->head = tnode;
		}
		huff->lhead->next = tnode;
		tnode->prev = huff->lhead;
		tnode->left = tnode->right = NULL;
 
		if (huff->lhead->parent) {
			if (huff->lhead->parent->left == huff->lhead) { /* lhead is guaranteed to by the NYT */
				huff->lhead->parent->left = tnode2;
			} else {
				huff->lhead->parent->right = tnode2;
			}
		} else {
			huff->tree = tnode2; 
		}
 
		tnode2->right = tnode;
		tnode2->left = huff->lhead;
 
		tnode2->parent = huff->lhead->parent;
		huff->lhead->parent = tnode->parent = tnode2;
     
		huff->loc[ch] = tnode;
 
		increment(huff, tnode2->parent);
	} else {
		increment(huff, huff->loc[ch]);
	}
}


/* Get a symbol */
static int Huff_Receive (node_t *node, int *ch, byte *fin) {
	while (node && node->symbol == INTERNAL_NODE) {
		if (get_bit(fin)) {
			node = node->right;
		} else {
			node = node->left;
		}
	}
	if (!node) {
		return 0;
	}
	return (*ch = node->symbol);
}


/* Send the prefix code for this node */
static void send(node_t *node, node_t *child, byte *fout) {
	if (node->parent) {
		send(node->parent, node, fout);
	}
	if (child) {
		if (node->right == child) {
			add_bit(1, fout);
		} else {
			add_bit(0, fout);
		}
	}
}


/* Send a symbol */
static void Huff_transmit (huff_t *huff, int ch, byte *fout) {
	int i;
	if (huff->loc[ch] == NULL) { 
		/* node_t hasn't been transmitted, send a NYT, then the symbol */
		Huff_transmit(huff, NYT, fout);
		for (i = 7; i >= 0; i--) {
			add_bit((char)((ch >> i) & 0x1), fout);
		}
	} else {
		send(huff->loc[ch], NULL, fout);
	}
}


void DynHuff_Decompress(msg_t *mbuf, int offset) {
	int			ch, cch, i, j, size;
	byte		seq[65536];
	byte*		buffer;
	huff_t		huff;

	size = mbuf->cursize - offset;
	buffer = mbuf->data + offset;

	if ( size <= 0 ) {
		return;
	}

	Com_Memset(&huff, 0, sizeof(huff_t));
	// Initialize the tree & list with the NYT node 
	huff.tree = huff.lhead = huff.ltail = huff.loc[NYT] = &(huff.nodeList[huff.blocNode++]);
	huff.tree->symbol = NYT;
	huff.tree->weight = 0;
	huff.lhead->next = huff.lhead->prev = NULL;
	huff.tree->parent = huff.tree->left = huff.tree->right = NULL;

	cch = buffer[0]*256 + buffer[1];
	// don't overflow with bad messages
	if ( cch > mbuf->maxsize - offset ) {
		cch = mbuf->maxsize - offset;
	}
	bloc = 16;

	for ( j = 0; j < cch; j++ ) {
		ch = 0;
		// don't overflow reading from the messages
		// FIXME: would it be better to have a overflow check in get_bit ?
		if ( (bloc >> 3) > size ) {
			seq[j] = 0;
			break;
		}
		Huff_Receive(huff.tree, &ch, buffer);				/* Get a character */
		if ( ch == NYT ) {								/* We got a NYT, get the symbol associated with it */
			ch = 0;
			for ( i = 0; i < 8; i++ ) {
				ch = (ch<<1) + get_bit(buffer);
			}
		}

		seq[j] = ch;									/* Write symbol */

		Huff_addRef(&huff, (byte)ch);								/* Increment node */
	}
	mbuf->cursize = cch + offset;
	Com_Memcpy(mbuf->data + offset, seq, cch);
}

void DynHuff_Compress(msg_t *mbuf, int offset) {
	int			i, ch, size;
	byte		seq[65536];
	byte*		buffer;
	huff_t		huff;

	size = mbuf->cursize - offset;
	buffer = mbuf->data+ + offset;

	if (size<=0) {
		return;
	}

	Com_Memset(&huff, 0, sizeof(huff_t));
	// Add the NYT (not yet transmitted) node into the tree/list */
	huff.tree = huff.lhead = huff.loc[NYT] =  &(huff.nodeList[huff.blocNode++]);
	huff.tree->symbol = NYT;
	huff.tree->weight = 0;
	huff.lhead->next = huff.lhead->prev = NULL;
	huff.tree->parent = huff.tree->left = huff.tree->right = NULL;
	huff.loc[NYT] = huff.tree;

	seq[0] = (size>>8);
	seq[1] = size&0xff;

	bloc = 16;

	for (i=0; i<size; i++ ) {
		ch = buffer[i];
		Huff_transmit(&huff, ch, seq);						/* Transmit symbol */
		Huff_addRef(&huff, (byte)ch);								/* Do update */
	}

	bloc += 8;												// next byte

	mbuf->cursize = (bloc>>3) + offset;
	Com_Memcpy(mbuf->data+offset, seq, (bloc>>3));
}