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Simple Huffman code changes.

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No empty trees are codified with the simple Huffman code. The simple Huffman
code is simplified to be either a 1-bit code or 8-bit code for symbols.

Change-Id: I3e2813027b5a643862729339303d80197c497aff
This commit is contained in:
Vikas Arora 2012-04-27 05:51:13 +00:00 committed by James Zern
parent a2849bc502
commit 781c01f421
2 changed files with 23 additions and 32 deletions
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28
src/dec/vp8l.c
View File

@ -238,25 +238,17 @@ static int ReadHuffmanCode(int alphabet_size, VP8LDecoder* const dec,
int symbols[2];
int codes[2];
int code_lengths[2];
const int nbits = VP8LReadBits(br, 3);
const int num_symbols = 1 + ((nbits == 0) ? 0 : VP8LReadBits(br, 1));
if (nbits == 0) {
symbols[0] = 0;
const int num_symbols = VP8LReadBits(br, 1) + 1;
const int first_symbol_len_code = VP8LReadBits(br, 1);
// The first code is either 1 bit or 8 bit code.
symbols[0] = VP8LReadBits(br, (first_symbol_len_code == 0) ? 1 : 8);
codes[0] = 0;
code_lengths[0] = 0;
} else {
const int num_bits = (nbits - 1) * 2 + 4;
int i;
for (i = 0; i < num_symbols; ++i) {
symbols[i] = VP8LReadBits(br, num_bits);
if (symbols[i] >= alphabet_size) {
dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
return 0;
}
codes[i] = i;
code_lengths[i] = num_symbols - 1;
}
code_lengths[0] = num_symbols - 1;
// The second code (if present), is always 8 bit long.
if (num_symbols == 2) {
symbols[1] = VP8LReadBits(br, 8);
codes[1] = 1;
code_lengths[1] = num_symbols - 1;
}
ok = HuffmanTreeBuildExplicit(tree, code_lengths, codes,
symbols, num_symbols);

25
src/enc/vp8l.c
View File

@ -531,20 +531,19 @@ static int StoreHuffmanCode(VP8LBitWriter* const bw,
++count;
}
}
if (count <= 2) {
int num_bits = 4;
// 0, 1 or 2 symbols to encode.
VP8LWriteBits(bw, 1, 1);
if (count == 0) {
VP8LWriteBits(bw, 3, 0);
ok = 1;
goto End;
}
while (symbols[count - 1] >= (1 << num_bits)) num_bits += 2;
VP8LWriteBits(bw, 3, (num_bits - 4) / 2 + 1);
if (count == 0) count = 1;
if (count <= 2 && symbols[0] < 256 && symbols[1] < 256) {
VP8LWriteBits(bw, 1, 1); // Small tree marker to encode 1 or 2 symbols.
VP8LWriteBits(bw, 1, count - 1);
for (i = 0; i < count; ++i) {
VP8LWriteBits(bw, num_bits, symbols[i]);
if (symbols[0] <= 1) {
VP8LWriteBits(bw, 1, 0); // Code bit for small (1 bit) symbol value.
VP8LWriteBits(bw, 1, symbols[0]);
} else {
VP8LWriteBits(bw, 1, 1);
VP8LWriteBits(bw, 8, symbols[0]);
}
if (count == 2) {
VP8LWriteBits(bw, 8, symbols[1]);
}
ok = 1;
goto End;