QPointF hash function

qpointf_hash.cpp

namespace std {
template<> struct hash<QPointF>
{
    size_t operator()(const QPointF &point, size_t seed) const
    {
        size_t x = static_cast<size_t>(point.x());
        size_t y = static_cast<size_t>(point.y());
        size_t half_qreal = sizeof(qreal) / 2;
        size_t half_bits = half_qreal*8;



        size_t half1s = pow(2, half_qreal*8)-1;
        size_t swappedX = (x & half1s) << half_bits | (x & (half1s << half_bits)) >> half_bits;
        return (swappedX | y) ^ seed;
    }
};
}

From Marc Mutz' presentation on Qt Container changes between Qt 5 and Qt 6, 20230913.
He asked us to implement a qHash function for hashing QPointF, which meets all the requirements for QHash.

Note that this is a bit odd because it does not make the assumption that qreal is a 64 bit type, since this can be altered when compiling Qt using the -qreal option.