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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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30
src/dec/vp8l.c
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@ -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;
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;
}
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] = 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);