huffman.cpp

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/* xoreos - A reimplementation of BioWare's Aurora engine
 *
 * xoreos is the legal property of its developers, whose names
 * can be found in the AUTHORS file distributed with this source
 * distribution.
 *
 * xoreos is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 3
 * of the License, or (at your option) any later version.
 *
 * xoreos is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with xoreos. If not, see <http://www.gnu.org/licenses/>.
 */

#include <cassert>

#include "src/common/huffman.h"
#include "src/common/util.h"
#include "src/common/error.h"
#include "src/common/bitstream.h"

namespace Common {

Huffman::Symbol::Symbol(uint32 c, uint32 s) : code(c), symbol(s) {
}


Huffman::Huffman(const HuffmanTable &table) {
    init(table.maxLength, table.codeCount, table.codes, table.lengths, table.symbols);
}

Huffman::Huffman(uint8 maxLength, size_t codeCount, const uint32 *codes,
                 const uint8 *lengths, const uint32 *symbols) {

    init(maxLength, codeCount, codes, lengths, symbols);
}

void Huffman::init(uint8 maxLength, size_t codeCount, const uint32 *codes,
                   const uint8 *lengths, const uint32 *symbols) {

    assert(codeCount > 0);

    assert(codes);
    assert(lengths);

    if (maxLength == 0)
        for (size_t i = 0; i < codeCount; i++)
            maxLength = MAX(maxLength, lengths[i]);

    assert(maxLength <= 32);

    _codes.resize(maxLength);
    _symbols.resize(codeCount);

    for (size_t i = 0; i < codeCount; i++) {
        // The symbol. If none were specified, just assume it's identical to the code index
        uint32 symbol = symbols ? symbols[i] : i;

        // Put the code and symbol into the correct list
        _codes[lengths[i] - 1].push_back(Symbol(codes[i], symbol));

        // And put the pointer to the symbol/code struct into the symbol list.
        _symbols[i] = &_codes[lengths[i] - 1].back();
    }
}

Huffman::~Huffman() {
}

void Huffman::setSymbols(const uint32 *symbols) {
    for (size_t i = 0; i < _symbols.size(); i++)
        _symbols[i]->symbol = symbols ? *symbols++ : i;
}

uint32 Huffman::getSymbol(BitStream &bits) const {
    uint32 code = 0;

    for (size_t i = 0; i < _codes.size(); i++) {
        bits.addBit(code, i);

        for (CodeList::const_iterator cCode = _codes[i].begin(); cCode != _codes[i].end(); ++cCode)
            if (code == cCode->code)
                return cCode->symbol;
    }

    throw Exception("Unknown Huffman code");
}

} // End of namespace Common