presto-main/src/main/java/io/prestosql/operator/SimplePagesHashStrategy.java/SimplePagesHashStrategy/hashPosition
class SimplePagesHashStrategy:    @Override
    public long hashPosition(int blockIndex, int position)
    {
        if (precomputedHashChannel != null) {
            return BIGINT.getLong(precomputedHashChannel.get(blockIndex), position);
        }
        long result = 0;
        for (int hashChannel : hashChannels) {
            Type type = types.get(hashChannel);
            Block block = channels.get(hashChannel).get(blockIndex);
            result = result * 31 + TypeUtils.hashPosition(type, block, position);
        }
        return result;
    }