stuff-from-scratch/src/base/compression/huffman/HuffmanCodeLengthTable.cpp

#include "HuffmanCodeLengthTable.h"

#include "ByteUtils.h"
#include "RunLengthEncoder.h"
#include "BitStream.h"

#include <algorithm>
#include <sstream>
#include <iostream>

void HuffmanCodeLengthTable::buildCompressedLengthSequence()
{
    RunLengthEncoder rl_encoder;
    auto rle_encoded = rl_encoder.encode(mInputLengthSequence);

    for (const auto& entry : rle_encoded)
    {
        //std::cout << "Got rle " << static_cast<int>(entry.first) << " | " << entry.second << std::endl;
    }
    mCompressedLengthSequence.clear();

    for (const auto& entry : rle_encoded)
    {
        const auto length = entry.first;
        const auto count = entry.second;
        if (count < 3)
        {
            for(std::size_t idx=0; idx<count; idx++)
            {
                mCompressedLengthSequence.push_back({length, 0});
            }
        }
        else if (length == 0)
        {
            std::size_t num_big = count / 138;
            for(std::size_t idx=0; idx<num_big; idx++)
            {
                mCompressedLengthSequence.push_back({18, 127});
            }
            auto remainder_big = count % 138;
            if (remainder_big > 10)
            {
                mCompressedLengthSequence.push_back({18, remainder_big-11});
            }
            else if(remainder_big > 2)
            {
                mCompressedLengthSequence.push_back({17, remainder_big-3});
            }
            else
            {
                for(std::size_t idx=0; idx<remainder_big; idx++)
                {
                    mCompressedLengthSequence.push_back({0, 0});
                }
            }
        }
        else
        {
            mCompressedLengthSequence.push_back({length, 0});
            auto num_blocks_of_six = (count-1)/6;
            for(std::size_t idx=0; idx<num_blocks_of_six; idx++)
            {
                mCompressedLengthSequence.push_back({16, 3});
            }
            auto remaining_counts = (count-1) % 6;
            if (remaining_counts >= 3)
            {
                mCompressedLengthSequence.push_back({16, remaining_counts - 3});
            }
            else
            {
                for(std::size_t idx=0; idx<remaining_counts; idx++)
                {
                    mCompressedLengthSequence.push_back({length, 0});
                }
            }
        }
    }

    mCompressedLengthCounts = std::vector<std::size_t>(19, 0);
    for (const auto& entry : mCompressedLengthSequence)
    {
        mCompressedLengthCounts[entry.first]++;
    }
}

const std::vector<HuffmanCodeLengthTable::CompressedSequenceEntry>& HuffmanCodeLengthTable::getCompressedLengthSequence() const
{
    return mCompressedLengthSequence;
}

const std::vector<std::size_t> HuffmanCodeLengthTable::getCompressedLengthCounts() const
{
    return mCompressedLengthCounts;
}

std::optional<PrefixCode> HuffmanCodeLengthTable::getCodeForSymbol(unsigned symbol) const
{
    return mTree.getCode(symbol);
}

bool HuffmanCodeLengthTable::readNextSymbol(unsigned& result, BitStream* stream)
{
    if (getNumCodeLengths() == 0)
    {
        return false;
    }

    std::size_t working_index{0};
    auto length = getCodeLength(working_index);
    auto delta = length;

    bool found{false};
    unsigned char buffer{0};
    uint32_t working_bits{0};
    unsigned working_symbol{0};

    while(!found)
    {
        auto valid = stream->readNextNBits(delta, buffer);
        //std::cout << "Got buffer " << ByteUtils::toString(buffer) << std::endl;;

        unsigned hold = buffer;
        working_bits = working_bits | (hold << (length - delta));
        //std::cout << "Read " << delta << " bits with length " << length << " and value " << ByteUtils::toString(working_bits) << std::endl;

        if (const auto symbol = findMatch(working_index, working_bits))
        {
            found = true;
            working_symbol = *symbol;
        }
        else
        {
            working_index++;
            if (working_index >= getNumCodeLengths())
            {
                break;
            }

            auto new_length = getCodeLength(working_index);
            delta = new_length - length;
            length = new_length;
        }
    }

    if (found)
    {
        result = working_symbol;
        // std::cout << "Found symbol " << working_symbol << " with bits " << ByteUtils::toString(working_bits) << std::endl;
        // std::cout << "At Byte offset " << stream->getCurrentByteOffset() << " and bit offset " << stream->getCurrentBitOffset() << std::endl;
        return true;
    }
    else
    {
        //std::cout << "SYMBOL NOT FOUND " << " with bits " << ByteUtils::toString(working_bits) << " and index " << working_index << std::endl;
        return false;
    }
}

void HuffmanCodeLengthTable::buildPrefixCodes()
{
    if(mInputLengthSequence.empty())
    {
        return;
    }

    unsigned char max_length = *std::max_element(mInputLengthSequence.begin(), mInputLengthSequence.end());
    std::vector<unsigned> counts(max_length+1, 0);
    for (const auto length : mInputLengthSequence)
    {
        counts[length]++;
    }
    counts[0] = 0;

    uint32_t code{0};
    std::vector<uint32_t> next_code(max_length + 1, 0);
    for (unsigned bits = 1; bits <= max_length; bits++)
    {
        code = (code + counts[bits-1]) << 1;
        //std::cout << "Start code for bit " << bits << " is " << ByteUtils::toString(code) << " | dec " << code << " count " << counts[bits-1] << std::endl;
        next_code[bits] = code;
    }

    for(std::size_t idx=0; idx<mInputLengthSequence.size(); idx++)
    {
        if (const auto length = mInputLengthSequence[idx]; length != 0)
        {
            const auto code = next_code[length];
            next_code[length]++;
            auto prefix_code = PrefixCode(code, length);
            mTree.addCodeLengthEntry(length, {PrefixCode(code, length), static_cast<unsigned>(idx)});
            mCodes.push_back(prefix_code);
        }
    }
    mTree.sortTable();
    //std::cout << dumpPrefixCodes();
}

const PrefixCode& HuffmanCodeLengthTable::getCode(std::size_t index) const
{
    return mCodes[index];
}

std::string HuffmanCodeLengthTable::dumpPrefixCodes() const
{
    return mTree.dump();
}

std::size_t HuffmanCodeLengthTable::mapToDeflateIndex(std::size_t index) const
{
    if (index>= DEFLATE_PERMUTATION_SIZE)
    {
        return 0;
    }
    else
    {
        return DEFLATE_PERMUTATION[index];
    }
}

std::size_t HuffmanCodeLengthTable::getNumCodeLengths() const
{
    return mTree.getNumCodeLengths();
}

std::optional<HuffmanTree::Symbol> HuffmanCodeLengthTable::findMatch(std::size_t treeIndex, uint32_t code) const
{
    return mTree.findMatch(treeIndex, code);
}

unsigned HuffmanCodeLengthTable::getCodeLength(std::size_t index) const
{
    return mTree.getCodeLength(index);
}

void HuffmanCodeLengthTable::setInputLengthSequence(const std::vector<unsigned char>& sequence, bool targetDeflate)
{
    mTargetDeflate = targetDeflate;

    if (targetDeflate)
    {
        mInputLengthSequence = std::vector<unsigned char>(DEFLATE_PERMUTATION_SIZE, 0);
        for(std::size_t idx=0; idx<sequence.size(); idx++)
        {
            mInputLengthSequence[mapToDeflateIndex(idx)] = sequence[idx];
            //std::cout << "Got code length for " << mapToDeflateIndex(idx) << " of " << static_cast<unsigned>(sequence[idx]) << std::endl;
        }
    }
    else
    {
        mInputLengthSequence = sequence;
    }
}