Function ExecHashGetBucketAndBatch

src/backend/executor/nodeHash.c:2221–2241

* ExecHashGetBucketAndBatch * Determine the bucket number and batch number for a hash value * * Note: on-the-fly increases of nbatch must not change the bucket number * for a given hash code (since we don't move tuples to different hash * chains), and must only cause the batch number to remain the same or * increase. Our algorithm is * bucketno = hashvalue MOD nbuckets * batchno = ROR(

 * than to lose the ability to divide batches.
 */
void
ExecHashGetBucketAndBatch(HashJoinTable hashtable,
						  uint32 hashvalue,
						  int *bucketno,
						  int *batchno)
{
	uint32		nbuckets = (uint32) hashtable->nbuckets;
	uint32		nbatch = (uint32) hashtable->nbatch;

	if (nbatch > 1)
	{
		*bucketno = hashvalue & (nbuckets - 1);
		*batchno = pg_rotate_right32(hashvalue,
									 hashtable->log2_nbuckets) & (nbatch - 1);
	}
	else
	{
		*bucketno = hashvalue & (nbuckets - 1);
		*batchno = 0;
	}
}

/*
 * ExecScanHashBucket