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Brotli format change: small improvement to the encoding of Huffman codes

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Combine the HSKIP and the simple/complex Huffman code type bits.
This commit is contained in:
Zoltan Szabadka
2014-01-08 12:28:28 +01:00
parent efbc1a8965
commit 4c8c7fd31c
4 changed files with 32 additions and 25 deletions
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brotli/enc/encode.cc
+12 -10
View File
@@ -136,12 +136,16 @@ void StoreHuffmanTreeOfHuffmanTreeToBitMask(
if (num_codes == 1) {
codes_to_store = kCodeLengthCodes;
}
const int skip_two_first =
code_length_bitdepth[kStorageOrder[0]] == 0 &&
code_length_bitdepth[kStorageOrder[1]] == 0;
WriteBits(1, skip_two_first, storage_ix, storage);
for (int i = skip_two_first * 2; i < codes_to_store; ++i) {
int skip_some = 0; // skips none.
if (code_length_bitdepth[kStorageOrder[0]] == 0 &&
code_length_bitdepth[kStorageOrder[1]] == 0) {
skip_some = 2; // skips two.
if (code_length_bitdepth[kStorageOrder[2]] == 0) {
skip_some = 3; // skips three.
}
}
WriteBits(2, skip_some, storage_ix, storage);
for (int i = skip_some; i < codes_to_store; ++i) {
uint8_t len[] = { 2, 4, 3, 2, 2, 4 };
uint8_t bits[] = { 0, 5, 1, 3, 2, 13 };
int v = code_length_bitdepth[kStorageOrder[i]];
@@ -182,7 +186,7 @@ void StoreHuffmanCode(const EntropyCode<kSize>& code, int alphabet_size,
}
if (code.count_ == 0) { // emit minimal tree for empty cases
// bits: small tree marker: 1, count-1: 0, max_bits-sized encoding for 0
WriteBits(3 + max_bits, 0x01, storage_ix, storage);
WriteBits(4 + max_bits, 0x1, storage_ix, storage);
return;
}
if (code.count_ <= 4) {
@@ -202,7 +206,7 @@ void StoreHuffmanCode(const EntropyCode<kSize>& code, int alphabet_size,
}
}
// Small tree marker to encode 1-4 symbols.
WriteBits(1, 1, storage_ix, storage);
WriteBits(2, 1, storage_ix, storage);
WriteBits(2, code.count_ - 1, storage_ix, storage);
for (int i = 0; i < code.count_; ++i) {
WriteBits(max_bits, symbols[i], storage_ix, storage);
@@ -219,8 +223,6 @@ void StoreHuffmanCode(const EntropyCode<kSize>& code, int alphabet_size,
}
return;
}
WriteBits(1, 0, storage_ix, storage);
uint8_t huffman_tree[kSize];
uint8_t huffman_tree_extra_bits[kSize];
int huffman_tree_size = 0;
brotli/enc/literal_cost.cc
+1 -1
View File
@@ -51,7 +51,7 @@ void EstimateBitCostsForLiterals(size_t pos, size_t len, size_t mask,
histo = 1;
}
cost[masked_pos] = log2(static_cast<double>(in_window) / histo);
cost[masked_pos] += 0.03;
cost[masked_pos] += 0.029;
if (cost[masked_pos] < 1.0) {
cost[masked_pos] *= 0.5;
cost[masked_pos] += 0.5;