BlockState.cpp

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#include "Globals.h"
#include "BlockState.h"





BlockState::BlockState():
    mChecksum(initializeChecksum())
{
    // Nothing needed yet
}





BlockState::BlockState(const AString & aKey, const AString & aValue):
    mState({{aKey, aValue}}),
    mChecksum(initializeChecksum())
{
}





BlockState::BlockState(std::initializer_list<std::pair<const AString, AString>> aKeysAndValues):
    mState(aKeysAndValues),
    mChecksum(initializeChecksum())
{
}





BlockState::BlockState(const std::map<AString, AString> & aKeysAndValues):
    mState(aKeysAndValues),
    mChecksum(initializeChecksum())
{
}





BlockState::BlockState(std::map<AString, AString> && aKeysAndValues):
    mState(std::move(aKeysAndValues)),
    mChecksum(initializeChecksum())
{
}





BlockState::BlockState(const BlockState & aCopyFrom, std::initializer_list<std::pair<const AString, AString>> aAdditionalKeysAndValues):
    mState(aCopyFrom.mState)
{
    for (const auto & kav: aAdditionalKeysAndValues)
    {
        mState[kav.first] = kav.second;
    }
    mChecksum = initializeChecksum();
}





BlockState::BlockState(const BlockState & aCopyFrom, const std::map<AString, AString> & aAdditionalKeysAndValues):
    mState(aCopyFrom.mState)
{
    for (const auto & kav: aAdditionalKeysAndValues)
    {
        mState[kav.first] = kav.second;
    }
    mChecksum = initializeChecksum();
}





bool BlockState::operator <(const BlockState & aOther) const
{
    // Fast-return this using checksum
    if (mChecksum != aOther.mChecksum)
    {
        return (mChecksum < aOther.mChecksum);
    }

    // Can fast-return this due to how comparison works
    if (mState.size() != aOther.mState.size())
    {
        return (mState.size() < aOther.mState.size());
    }

    auto itA = mState.begin();
    auto itOther = aOther.mState.begin();

    // don't need to check itOther, size checks above ensure size(A) == size(O)
    while (itA != mState.end())
    {
        {
            const auto cmp = itA->first.compare(itOther->first);
            if (cmp != 0)
            {
                return (cmp < 0);
            }
        }
        {
            const auto cmp = itA->second.compare(itOther->second);
            if (cmp != 0)
            {
                return (cmp < 0);
            }
        }

        ++itA;
        ++itOther;
    }

    return false;
}





bool BlockState::operator ==(const BlockState & aOther) const
{
    // Fast-fail if the checksums differ or differrent counts:
    if ((mChecksum != aOther.mChecksum) || (mState.size() != aOther.mState.size()))
    {
        return false;
    }

    // Slow-check everything if the checksums match:
    return std::equal(mState.begin(), mState.end(), aOther.mState.begin());
}





const AString & BlockState::value(const AString & aKey) const
{
    auto itr = mState.find(aKey);
    if (itr == mState.end())
    {
        static AString empty;
        return empty;
    }
    return itr->second;
}





UInt32 BlockState::initializeChecksum()
{
    removeEmptyKeys();

    // Calculate the checksum as a XOR of all mState keys' and values' checksums
    // This way we don't depend on the std::map's ordering
    UInt32 res = 0;
    for (const auto & kv: mState)
    {
        auto partial = partialChecksum(kv.first) ^ partialChecksum(kv.second);
        res = res ^ partial;
    }
    return res;
}





void BlockState::removeEmptyKeys()
{
    for (auto itr = mState.begin(); itr != mState.end();)
    {
        if (itr->second.empty())
        {
            itr = mState.erase(itr);
        }
        else
        {
            ++itr;
        }
    }
}





UInt32 BlockState::partialChecksum(const AString & aString)
{
    UInt32 shift = 0;
    UInt32 res = 0;
    for (auto ch: aString)
    {
        UInt32 v = static_cast<UInt8>(ch);
        v = v << shift;
        shift = (shift + 1) % 24;
        res = res ^ v;
    }
    return res;
}