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Optimize lossless decoding for trivial(ARB) codes.

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Optimize the decoding for region that have trivial literal codes.
The trivial literal is defined as huffman image with Red, Blue and Alpha
huffman trees with only single code values.
This speeds up lossless decoding by 3%

Change-Id: I0204949917836f74c0eb4ba5a7f4052a4797833b
This commit is contained in:
Vikas Arora 2014-09-12 09:06:35 -07:00
parent 924fcfd900
commit f9ced95a9b
2 changed files with 28 additions and 4 deletions
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27
src/dec/vp8l.c
View File

@ -50,6 +50,9 @@ static const uint16_t kAlphabetSize[HUFFMAN_CODES_PER_META_CODE] = {
NUM_DISTANCE_CODES
};
static const uint8_t kLiteralMap[HUFFMAN_CODES_PER_META_CODE] = {
0, 1, 1, 1, 0
};
#define NUM_CODE_LENGTH_CODES 19
static const uint8_t kCodeLengthCodeOrder[NUM_CODE_LENGTH_CODES] = {
@ -359,8 +362,10 @@ static int ReadHuffmanCodes(VP8LDecoder* const dec, int xsize, int ysize,
next = huffman_tables;
for (i = 0; i < num_htree_groups; ++i) {
HuffmanCode** const htrees = htree_groups[i].htrees;
HTreeGroup* const htree_group = &htree_groups[i];
HuffmanCode** const htrees = htree_group->htrees;
int size;
int is_trivial_literal = 1;
for (j = 0; j < HUFFMAN_CODES_PER_META_CODE; ++j) {
int alphabet_size = kAlphabetSize[j];
htrees[j] = next;
@ -368,11 +373,22 @@ static int ReadHuffmanCodes(VP8LDecoder* const dec, int xsize, int ysize,
alphabet_size += 1 << color_cache_bits;
}
size = ReadHuffmanCode(alphabet_size, dec, code_lengths, next);
if (is_trivial_literal && kLiteralMap[j] == 1) {
is_trivial_literal = (next->bits == 0);
}
next += size;
if (size == 0) {
goto Error;
}
}
htree_group->is_trivial_literal = is_trivial_literal;
if (is_trivial_literal) {
const int red = htrees[RED][0].value;
const int blue = htrees[BLUE][0].value;
const int alpha = htrees[ALPHA][0].value;
htree_group->literal_arb =
((uint32_t)alpha << 24) | (red << 16) | blue;
}
}
WebPSafeFree(code_lengths);
@ -983,13 +999,16 @@ static int DecodeImageData(VP8LDecoder* const dec, uint32_t* const data,
VP8LFillBitWindow(br);
code = ReadSymbol(htree_group->htrees[GREEN], br);
if (code < NUM_LITERAL_CODES) { // Literal
int red, green, blue, alpha;
if (htree_group->is_trivial_literal) {
*src = htree_group->literal_arb | (code << 8);
} else {
int red, blue, alpha;
red = ReadSymbol(htree_group->htrees[RED], br);
green = code;
VP8LFillBitWindow(br);
blue = ReadSymbol(htree_group->htrees[BLUE], br);
alpha = ReadSymbol(htree_group->htrees[ALPHA], br);
*src = ((uint32_t)alpha << 24) | (red << 16) | (green << 8) | blue;
*src = ((uint32_t)alpha << 24) | (red << 16) | (code << 8) | blue;
}
AdvanceByOne:
++src;
++col;

5
src/utils/huffman.h
View File

@ -39,6 +39,11 @@ typedef struct {
typedef struct HTreeGroup HTreeGroup;
struct HTreeGroup {
HuffmanCode* htrees[HUFFMAN_CODES_PER_META_CODE];
int is_trivial_literal; // True, if huffman trees for Red, Blue & Alpha
// Symbols are trivial (have a single code).
uint32_t literal_arb; // If is_trivial_literal is true, this is the
// ARGB value of the pixel, with Green channel
// being set to zero.
};
// Creates the instance of HTreeGroup with specified number of tree-groups.