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merge all tree processing into a single VP8LProcessTree()

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-> 0.1% size improvement because we're calling OptimizeForRLE()
systematically now.

Change-Id: I03bd712175728e0d46323f375134cae5a241db4b
This commit is contained in:
Pascal Massimino 2012-05-14 05:49:02 -07:00
parent 9c7a3cf5e7
commit c6882c49e3
3 changed files with 155 additions and 162 deletions
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153
src/enc/vp8l.c
View File

@ -155,114 +155,6 @@ static int VP8LEncAnalyze(VP8LEncoder* const enc) {
return 1;
}
// -----------------------------------------------------------------------------
// Heuristics for selecting the stride ranges to collapse.
static int ValuesShouldBeCollapsedToStrideAverage(int a, int b) {
return abs(a - b) < 4;
}
// Change the population counts in a way that the consequent
// Hufmann tree compression, especially its rle-part will be more
// likely to compress this data more efficiently.
//
// length contains the size of the histogram.
// data contains the population counts.
static int OptimizeHuffmanForRle(int length, int* counts) {
int stride;
int limit;
int sum;
uint8_t* good_for_rle;
// 1) Let's make the Huffman code more compatible with rle encoding.
int i;
for (; length >= 0; --length) {
if (length == 0) {
return 1; // All zeros.
}
if (counts[length - 1] != 0) {
// Now counts[0..length - 1] does not have trailing zeros.
break;
}
}
// 2) Let's mark all population counts that already can be encoded
// with an rle code.
good_for_rle = (uint8_t*)calloc(length, 1);
if (good_for_rle == NULL) {
return 0;
}
{
// Let's not spoil any of the existing good rle codes.
// Mark any seq of 0's that is longer as 5 as a good_for_rle.
// Mark any seq of non-0's that is longer as 7 as a good_for_rle.
int symbol = counts[0];
int stride = 0;
for (i = 0; i < length + 1; ++i) {
if (i == length || counts[i] != symbol) {
if ((symbol == 0 && stride >= 5) ||
(symbol != 0 && stride >= 7)) {
int k;
for (k = 0; k < stride; ++k) {
good_for_rle[i - k - 1] = 1;
}
}
stride = 1;
if (i != length) {
symbol = counts[i];
}
} else {
++stride;
}
}
}
// 3) Let's replace those population counts that lead to more rle codes.
stride = 0;
limit = counts[0];
sum = 0;
for (i = 0; i < length + 1; ++i) {
if (i == length || good_for_rle[i] ||
(i != 0 && good_for_rle[i - 1]) ||
!ValuesShouldBeCollapsedToStrideAverage(counts[i], limit)) {
if (stride >= 4 || (stride >= 3 && sum == 0)) {
int k;
// The stride must end, collapse what we have, if we have enough (4).
int count = (sum + stride / 2) / stride;
if (count < 1) {
count = 1;
}
if (sum == 0) {
// Don't make an all zeros stride to be upgraded to ones.
count = 0;
}
for (k = 0; k < stride; ++k) {
// We don't want to change value at counts[i],
// that is already belonging to the next stride. Thus - 1.
counts[i - k - 1] = count;
}
}
stride = 0;
sum = 0;
if (i < length - 3) {
// All interesting strides have a count of at least 4,
// at least when non-zeros.
limit = (counts[i] + counts[i + 1] +
counts[i + 2] + counts[i + 3] + 2) / 4;
} else if (i < length) {
limit = counts[i];
} else {
limit = 0;
}
}
++stride;
if (i != length) {
sum += counts[i];
if (stride >= 4) {
limit = (sum + stride / 2) / stride;
}
}
}
free(good_for_rle);
return 1;
}
static int GetHuffBitLengthsAndCodes(
const VP8LHistogramSet* const histogram_image,
@ -312,34 +204,11 @@ static int GetHuffBitLengthsAndCodes(
for (i = 0; i < histogram_image_size; ++i) {
HuffmanTreeCode* const codes = &huffman_codes[5 * i];
VP8LHistogram* const histo = histogram_image->histograms[i];
const int num_literals = codes[0].num_symbols;
// For each component, optimize histogram for Huffman with RLE compression,
// and create a Huffman tree (in the form of bit lengths) for each.
ok = ok && OptimizeHuffmanForRle(num_literals, histo->literal_);
ok = ok && VP8LCreateHuffmanTree(histo->literal_, num_literals, 15,
codes[0].code_lengths);
ok = ok && OptimizeHuffmanForRle(256, histo->red_);
ok = ok && VP8LCreateHuffmanTree(histo->red_, 256, 15,
codes[1].code_lengths);
ok = ok && OptimizeHuffmanForRle(256, histo->blue_);
ok = ok && VP8LCreateHuffmanTree(histo->blue_, 256, 15,
codes[2].code_lengths);
ok = ok && OptimizeHuffmanForRle(256, histo->alpha_);
ok = ok && VP8LCreateHuffmanTree(histo->alpha_, 256, 15,
codes[3].code_lengths);
ok = ok && OptimizeHuffmanForRle(DISTANCE_CODES_MAX, histo->distance_);
ok = ok && VP8LCreateHuffmanTree(histo->distance_, DISTANCE_CODES_MAX, 15,
codes[4].code_lengths);
// Create the actual bit codes for the bit lengths.
// TODO(vikasa): merge with each VP8LCreateHuffmanTree() ?
for (k = 0; k < 5; ++k) {
VP8LConvertBitDepthsToSymbols(codes + k);
}
ok = ok && VP8LCreateHuffmanTree(histo->literal_, 15, codes + 0);
ok = ok && VP8LCreateHuffmanTree(histo->red_, 15, codes + 1);
ok = ok && VP8LCreateHuffmanTree(histo->blue_, 15, codes + 2);
ok = ok && VP8LCreateHuffmanTree(histo->alpha_, 15, codes + 3);
ok = ok && VP8LCreateHuffmanTree(histo->distance_, 15, codes + 4);
}
End:
@ -423,6 +292,10 @@ static int StoreFullHuffmanCode(VP8LBitWriter* const bw,
(HuffmanTreeToken*)malloc(bit_lengths_size * sizeof(*tokens));
if (tokens == NULL) return 0;
huffman_code.num_symbols = CODE_LENGTH_CODES;
huffman_code.code_lengths = code_length_bitdepth;
huffman_code.codes = code_length_bitdepth_symbols;
VP8LWriteBits(bw, 1, 0);
num_tokens = VP8LCreateCompressedHuffmanTree(bit_lengths, bit_lengths_size,
tokens, bit_lengths_size);
@ -433,17 +306,11 @@ static int StoreFullHuffmanCode(VP8LBitWriter* const bw,
++histogram[tokens[i].code];
}
if (!VP8LCreateHuffmanTree(histogram, CODE_LENGTH_CODES,
7, code_length_bitdepth)) {
if (!VP8LCreateHuffmanTree(histogram, 7, &huffman_code)) {
goto End;
}
}
huffman_code.num_symbols = CODE_LENGTH_CODES;
huffman_code.code_lengths = code_length_bitdepth;
huffman_code.codes = code_length_bitdepth_symbols;
VP8LConvertBitDepthsToSymbols(&huffman_code);
StoreHuffmanTreeOfHuffmanTreeToBitMask(bw, code_length_bitdepth);
ClearHuffmanTreeIfOnlyOneSymbol(&huffman_code);
{

142
src/utils/huffman_encode.c
View File

@ -20,6 +20,112 @@
#include <stdlib.h>
#include <string.h>
// -----------------------------------------------------------------------------
// Util function to optimize the symbol map for RLE coding
// Heuristics for selecting the stride ranges to collapse.
static int ValuesShouldBeCollapsedToStrideAverage(int a, int b) {
return abs(a - b) < 4;
}
// Change the population counts in a way that the consequent
// Hufmann tree compression, especially its RLE-part, give smaller output.
static int OptimizeHuffmanForRle(int length, int* const counts) {
int stride;
int limit;
int sum;
uint8_t* good_for_rle;
// 1) Let's make the Huffman code more compatible with rle encoding.
int i;
for (; length >= 0; --length) {
if (length == 0) {
return 1; // All zeros.
}
if (counts[length - 1] != 0) {
// Now counts[0..length - 1] does not have trailing zeros.
break;
}
}
// 2) Let's mark all population counts that already can be encoded
// with an rle code.
good_for_rle = (uint8_t*)calloc(length, 1);
if (good_for_rle == NULL) {
return 0;
}
{
// Let's not spoil any of the existing good rle codes.
// Mark any seq of 0's that is longer as 5 as a good_for_rle.
// Mark any seq of non-0's that is longer as 7 as a good_for_rle.
int symbol = counts[0];
int stride = 0;
for (i = 0; i < length + 1; ++i) {
if (i == length || counts[i] != symbol) {
if ((symbol == 0 && stride >= 5) ||
(symbol != 0 && stride >= 7)) {
int k;
for (k = 0; k < stride; ++k) {
good_for_rle[i - k - 1] = 1;
}
}
stride = 1;
if (i != length) {
symbol = counts[i];
}
} else {
++stride;
}
}
}
// 3) Let's replace those population counts that lead to more rle codes.
stride = 0;
limit = counts[0];
sum = 0;
for (i = 0; i < length + 1; ++i) {
if (i == length || good_for_rle[i] ||
(i != 0 && good_for_rle[i - 1]) ||
!ValuesShouldBeCollapsedToStrideAverage(counts[i], limit)) {
if (stride >= 4 || (stride >= 3 && sum == 0)) {
int k;
// The stride must end, collapse what we have, if we have enough (4).
int count = (sum + stride / 2) / stride;
if (count < 1) {
count = 1;
}
if (sum == 0) {
// Don't make an all zeros stride to be upgraded to ones.
count = 0;
}
for (k = 0; k < stride; ++k) {
// We don't want to change value at counts[i],
// that is already belonging to the next stride. Thus - 1.
counts[i - k - 1] = count;
}
}
stride = 0;
sum = 0;
if (i < length - 3) {
// All interesting strides have a count of at least 4,
// at least when non-zeros.
limit = (counts[i] + counts[i + 1] +
counts[i + 2] + counts[i + 3] + 2) / 4;
} else if (i < length) {
limit = counts[i];
} else {
limit = 0;
}
}
++stride;
if (i != length) {
sum += counts[i];
if (stride >= 4) {
limit = (sum + stride / 2) / stride;
}
}
}
free(good_for_rle);
return 1;
}
typedef struct {
int total_count_;
int value_;
@ -58,7 +164,13 @@ static void SetBitDepths(const HuffmanTree* const tree,
}
}
// This function will create a Huffman tree.
// Create an optimal Huffman tree.
//
// (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 occurred.
//
// The catch here is that the tree cannot be arbitrarily deep
//
@ -71,18 +183,21 @@ static void SetBitDepths(const HuffmanTree* const tree,
// we are not planning to use this with extremely long blocks.
//
// See http://en.wikipedia.org/wiki/Huffman_coding
int VP8LCreateHuffmanTree(const int* const histogram, int histogram_size,
int tree_depth_limit, uint8_t* const bit_depths) {
static int GenerateOptimalTree(const int* const histogram, int histogram_size,
int tree_depth_limit,
uint8_t* const bit_depths) {
int count_min;
HuffmanTree* tree_pool;
HuffmanTree* tree;
int tree_size_orig = 0;
int i;
for (i = 0; i < histogram_size; ++i) {
if (histogram[i] != 0) {
++tree_size_orig;
}
}
// 3 * tree_size is enough to cover all the nodes representing a
// population and all the inserted nodes combining two existing nodes.
// The tree pool needs 2 * (tree_size_orig - 1) entities, and the
@ -282,7 +397,8 @@ static uint32_t ReverseBits(int num_bits, uint32_t bits) {
return retval;
}
void VP8LConvertBitDepthsToSymbols(HuffmanTreeCode* const tree) {
// Get the actual bit values for a tree of bit depths.
static void ConvertBitDepthsToSymbols(HuffmanTreeCode* const tree) {
// 0 bit-depth means that the symbol does not exist.
int i;
int len;
@ -311,4 +427,22 @@ void VP8LConvertBitDepthsToSymbols(HuffmanTreeCode* const tree) {
}
}
// -----------------------------------------------------------------------------
// Main entry point
int VP8LCreateHuffmanTree(int* const histogram, int tree_depth_limit,
HuffmanTreeCode* const tree) {
const int num_symbols = tree->num_symbols;
if (!OptimizeHuffmanForRle(num_symbols, histogram)) {
return 0;
}
if (!GenerateOptimalTree(histogram, num_symbols,
tree_depth_limit, tree->code_lengths)) {
return 0;
}
// Create the actual bit codes for the bit lengths.
ConvertBitDepthsToSymbols(tree);
return 1;
}
#endif

22
src/utils/huffman_encode.h
View File

@ -20,24 +20,15 @@
extern "C" {
#endif
// Create a Huffman tree.
//
// (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 occurred.
int VP8LCreateHuffmanTree(const int* data, const int length,
const int tree_limit, uint8_t* bit_depths);
// Turn the Huffman tree into a token sequence.
// Returns the number of tokens used.
// Struct for holding the tree header in coded form.
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,
// Turn the Huffman tree into a token sequence.
// Returns the number of tokens used.
int VP8LCreateCompressedHuffmanTree(const uint8_t* const depth, int depth_size,
HuffmanTreeToken* tokens, int max_tokens);
// Struct to represent the tree codes (depth and bits array).
@ -47,8 +38,9 @@ typedef struct {
uint16_t* codes; // Symbol Codes.
} HuffmanTreeCode;
// Get the actual bit values for a tree of bit depths.
void VP8LConvertBitDepthsToSymbols(HuffmanTreeCode* const tree);
// Create an optimized tree, and tokenize it.
int VP8LCreateHuffmanTree(int* const histogram, int tree_depth_limit,
HuffmanTreeCode* const tree);
#if defined(__cplusplus) || defined(c_plusplus)
}