dany/libwebp
1
0
Fork 0
mirror of https://github.com/webmproject/libwebp.git synced 2025-07-18 23:09:52 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity

clean-up around Huffman-encode

Browse Source 
* refine doc
* use LUT for bit-reversal
* added assert
* Introduce HuffmanTreeToken instead of separate code/extra_bits arrays

Change-Id: I0fe0b50b55eb43a4be9f730b1abe40632a6fa7f0
This commit is contained in:
Pascal Massimino
2012-05-10 09:11:47 -07:00
parent c579a71012
commit 9f566d1d36
3 changed files with 134 additions and 142 deletions
Download Patch File Download Diff File Expand all files Collapse all files

38
src/utils/huffman_encode.h
View File

@ -7,7 +7,7 @@
//
// Author: jyrki@google.com (Jyrki Alakuijala)
//
// Flate like entropy encoding (Huffman) for webp lossless
// Flate-like entropy encoding (Huffman) for webp lossless
#ifndef WEBP_UTILS_HUFFMAN_ENCODE_H_
#define WEBP_UTILS_HUFFMAN_ENCODE_H_
@ -20,27 +20,29 @@
extern "C" {
#endif
// This function will create a Huffman tree.
// Create a Huffman tree.
//
// 'histogram' contains the population counts.
// 'tree_depth_limit' is the maximum bit depth of the Huffman codes.
// The created tree is returned as 'bit_depths', which stores how many bits are
// used for each symbol.
// See http://en.wikipedia.org/wiki/Huffman_coding
// Returns 0 on memory error.
int VP8LCreateHuffmanTree(const int* const histogram, int histogram_size,
int tree_depth_limit, uint8_t* const bit_depths);
// (data,length): population counts.
// tree_limit: maximum bit depth (inclusive) of the codes.
// bit_depths[]: how many bits are used for the symbol.
//
// Returns 0 when an error has occured.
int VP8LCreateHuffmanTree(const int* data, const int length,
const int tree_limit, uint8_t* bit_depths);
// Write a huffman tree from bit depths. The generated Huffman tree is
// compressed once more using a Huffman tree.
void VP8LCreateCompressedHuffmanTree(const uint8_t* const depth, int len,
int* num_symbols,
uint8_t* tree,
uint8_t* extra_bits_data);
// Turn the Huffman tree into a token sequence.
// Returns the number of tokens used.
typedef struct {
uint8_t code; // value (0..15) or escape code (16,17,18)
uint8_t extra_bits; // extra bits for escape codes
} HuffmanTreeToken;
int VP8LCreateCompressedHuffmanTree(const uint8_t* const depth, int len,
HuffmanTreeToken* tokens, int max_tokens);
// Get the actual bit values for a tree of bit depths.
void VP8LConvertBitDepthsToSymbols(const uint8_t* depth, int len,
uint16_t* bits);
void VP8LConvertBitDepthsToSymbols(const uint8_t* const depth, int len,
uint16_t* const bits);
#if defined(__cplusplus) || defined(c_plusplus)
}