Function cdbhashreduce

src/backend/cdb/cdbhash.c:252–285

* Reduce the hash to a segment number. */

 * Reduce the hash to a segment number.
 */
unsigned int
cdbhashreduce(CdbHash *h)
{
	int			result = 0;		/* TODO: what is a good initialization value?
								 * could we guarantee at this point that there
								 * will not be a negative segid in Cloudberry
								 * Database and therefore initialize to this
								 * value for error checking? */

	Assert(h->reducealg == REDUCE_BITMASK ||
		   h->reducealg == REDUCE_LAZYMOD ||
		   h->reducealg == REDUCE_JUMP_HASH);
	Assert(h->natts > 0);

	/*
	 * Reduce our 32-bit hash value to a segment number
	 */
	switch (h->reducealg)
	{
		case REDUCE_BITMASK:
			result = FASTMOD(h->hash, (uint32) h->numsegs); /* fast mod (bitmask) */
			break;

		case REDUCE_LAZYMOD:
			result = (h->hash) % (h->numsegs);	/* simple mod */
			break;

		case REDUCE_JUMP_HASH:
			result = jump_consistent_hash(h->hash, h->numsegs);
			break;
	}

	return result;
}

/*
 * Return a random segment number, for randomly distributed policy.