dany/libwebp
1
0
Fork 0
mirror of https://github.com/webmproject/libwebp.git synced 2025-07-13 14:34:33 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity

~20% faster lossless decoding

Browse Source 
We use help from small LUTs for Huffman decoding.

Change-Id: I58db4ecd37282822094519f2aa14cf544beba975
This commit is contained in:
skal
2013-06-20 09:41:29 +02:00
parent 313d853fa9
commit 24cc307ae3
3 changed files with 36 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
src/utils/huffman.c
View File

@ -13,6 +13,7 @@
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include "./huffman.h"
#include "../utils/utils.h"
#include "../webp/format_constants.h"
@ -57,6 +58,7 @@ static int TreeInit(HuffmanTree* const tree, int num_leaves) {
if (tree->root_ == NULL) return 0;
TreeNodeInit(tree->root_); // Initialize root.
tree->num_nodes_ = 1;
memset(tree->lut_bits_, 255, sizeof(tree->lut_bits_));
return 1;
}
@ -117,10 +119,30 @@ int HuffmanCodeLengthsToCodes(const int* const code_lengths,
return 1;
}
static int ReverseBits(int bits, int num_bits) {
int retval = 0;
int i;
for (i = 0; i < num_bits; ++i) {
retval <<= 1;
retval |= bits & 1;
bits >>= 1;
}
return retval;
}
static int TreeAddSymbol(HuffmanTree* const tree,
int symbol, int code, int code_length) {
HuffmanTreeNode* node = tree->root_;
const HuffmanTreeNode* const max_node = tree->root_ + tree->max_nodes_;
if (code_length <= HUFF_LUT_BITS) {
const int base_code = ReverseBits(code, code_length);
int i;
for (i = 0; i < (1 << (HUFF_LUT_BITS - code_length)); ++i) {
const int idx = base_code | (i << code_length);
tree->lut_symbol_[idx] = symbol;
tree->lut_bits_[idx] = code_length;
}
}
while (code_length-- > 0) {
if (node >= max_node) {
return 0;