93 lines
3.9 KiB
C++
93 lines
3.9 KiB
C++
|
/********************************************************************
|
||
|
|
* *
|
||
|
|
* THIS FILE IS PART OF THE OggTheora SOFTWARE CODEC SOURCE CODE. *
|
||
|
|
* USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS *
|
||
|
|
* GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
|
||
|
|
* IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING. *
|
||
|
|
* *
|
||
|
|
* THE Theora SOURCE CODE IS COPYRIGHT (C) 2002-2009 *
|
||
|
|
* by the Xiph.Org Foundation and contributors http://www.xiph.org/ *
|
||
|
|
* *
|
||
|
|
********************************************************************
|
||
|
|
|
||
|
|
function:
|
||
|
|
last mod: $Id: huffdec.h 16503 2009-08-22 18:14:02Z giles $
|
||
|
|
|
||
|
|
********************************************************************/
|
||
|
|
|
||
|
|
#if !defined(_huffdec_H)
|
||
|
|
# define _huffdec_H (1)
|
||
|
|
# include "huffman.h"
|
||
|
|
# include "bitpack.h"
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
typedef struct oc_huff_node oc_huff_node;
|
||
|
|
|
||
|
|
/*A node in the Huffman tree.
|
||
|
|
Instead of storing every branching in the tree, subtrees can be collapsed
|
||
|
|
into one node, with a table of size 1<<nbits pointing directly to its
|
||
|
|
descedents nbits levels down.
|
||
|
|
This allows more than one bit to be read at a time, and avoids following all
|
||
|
|
the intermediate branches with next to no increased code complexity once
|
||
|
|
the collapsed tree has been built.
|
||
|
|
We do _not_ require that a subtree be complete to be collapsed, but instead
|
||
|
|
store duplicate pointers in the table, and record the actual depth of the
|
||
|
|
node below its parent.
|
||
|
|
This tells us the number of bits to advance the stream after reaching it.
|
||
|
|
|
||
|
|
This turns out to be equivalent to the method described in \cite{Hash95},
|
||
|
|
without the requirement that codewords be sorted by length.
|
||
|
|
If the codewords were sorted by length (so-called ``canonical-codes''), they
|
||
|
|
could be decoded much faster via either Lindell and Moffat's approach or
|
||
|
|
Hashemian's Condensed Huffman Code approach, the latter of which has an
|
||
|
|
extremely small memory footprint.
|
||
|
|
We can't use Choueka et al.'s finite state machine approach, which is
|
||
|
|
extremely fast, because we can't allow multiple symbols to be output at a
|
||
|
|
time; the codebook can and does change between symbols.
|
||
|
|
It also has very large memory requirements, which impairs cache coherency.
|
||
|
|
|
||
|
|
@ARTICLE{Hash95,
|
||
|
|
author="Reza Hashemian",
|
||
|
|
title="Memory Efficient and High-Speed Search {Huffman} Coding",
|
||
|
|
journal="{IEEE} Transactions on Communications",
|
||
|
|
volume=43,
|
||
|
|
number=10,
|
||
|
|
pages="2576--2581",
|
||
|
|
month=Oct,
|
||
|
|
year=1995
|
||
|
|
}*/
|
||
|
|
struct oc_huff_node{
|
||
|
|
/*The number of bits of the code needed to descend through this node.
|
||
|
|
0 indicates a leaf node.
|
||
|
|
Otherwise there are 1<<nbits nodes in the nodes table, which can be
|
||
|
|
indexed by reading nbits bits from the stream.*/
|
||
|
|
unsigned char nbits;
|
||
|
|
/*The value of a token stored in a leaf node.
|
||
|
|
The value in non-leaf nodes is undefined.*/
|
||
|
|
unsigned char token;
|
||
|
|
/*The depth of the current node, relative to its parent in the collapsed
|
||
|
|
tree.
|
||
|
|
This can be less than its parent's nbits value, in which case there are
|
||
|
|
1<<nbits-depth copies of this node in the table, and the bitstream should
|
||
|
|
only be advanced depth bits after reaching this node.*/
|
||
|
|
unsigned char depth;
|
||
|
|
/*The table of child nodes.
|
||
|
|
The ACTUAL size of this array is 1<<nbits, despite what the declaration
|
||
|
|
below claims.
|
||
|
|
The exception is that for leaf nodes the size is 0.*/
|
||
|
|
oc_huff_node *nodes[2];
|
||
|
|
};
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
int oc_huff_trees_unpack(oc_pack_buf *_opb,
|
||
|
|
oc_huff_node *_nodes[TH_NHUFFMAN_TABLES]);
|
||
|
|
int oc_huff_trees_copy(oc_huff_node *_dst[TH_NHUFFMAN_TABLES],
|
||
|
|
const oc_huff_node *const _src[TH_NHUFFMAN_TABLES]);
|
||
|
|
void oc_huff_trees_clear(oc_huff_node *_nodes[TH_NHUFFMAN_TABLES]);
|
||
|
|
int oc_huff_token_decode(oc_pack_buf *_opb,const oc_huff_node *_node);
|
||
|
|
|
||
|
|
|
||
|
|
#endif
|