presto-main/src/main/java/io/prestosql/operator/HashGenerator.java/HashGenerator/getPartition
class HashGenerator:    default int getPartition(int partitionCount, int position, Page page)
    {
        long rawHash = hashPosition(position, page);

        // clear the sign bit
        rawHash &= 0x7fff_ffff_ffff_ffffL;

        int partition = (int) (rawHash % partitionCount);

        checkState(partition >= 0 && partition < partitionCount);
        return partition;
    }