int main(){
int x=3;
printf("%d\n",ispowof2(x));
x=4;
printf("%d\n",ispowof2(x));
return 0;
}
/*
* Create a CdbHash for this session.
*
* CdbHash maintains the following information about the hash.
* In here we set the variables that should not change in the scope of the newly created
* CdbHash, these are:
*
* 1 - number of segments in Greenplum Database.
* 2 - hashingalgorithm used.
* 3 - reduction method.
*
* The hash value itself will be initialized for every tuple in cdbhashinit()
*/
CdbHash *
makeCdbHash(int numsegs, CdbHashAlg algorithm)
{
CdbHash *h;
assert(numsegs > 0); /* verify number of segments is legal. */
assert(algorithm == HASH_FNV_1); /* make sure everybody uses same algorithm */
/* Create a pointer to a CdbHash that includes the hash properties */
h = palloc(sizeof(CdbHash));
/*
* set this hash session characteristics.
*/
h->hash = 0;
h->numsegs = numsegs;
h->hashalg = algorithm;
if (h->hashalg == HASH_FNV_1)
h->hashfn = &fnv1_32_buf;
else if (h->hashalg == HASH_FNV_1A)
h->hashfn = &fnv1a_32_buf;
/*
* set the reduction algorithm: If num_segs is power of 2 use bit mask,
* else use lazy mod (h mod n)
*/
if (ispowof2(numsegs))
{
h->reducealg = REDUCE_BITMASK;
}
else
{
h->reducealg = REDUCE_LAZYMOD;
}
/*
* if we distribute into a relation with an empty partitioning policy,
* we will round robin the tuples starting off from this index. Note that
* the random number is created one per makeCdbHash. This means that commands
* that create a cdbhash object only once for all tuples (like COPY,
* INSERT-INTO-SELECT) behave more like a round-robin distribution, while
* commands that create a cdbhash per row (like INSERT) behave more like a
* random distribution.
*/
h->rrindex = cdb_randint(0, UPPER_VAL);
ereport(DEBUG4,
(errmsg("CDBHASH started using algorithm %d into %d segment databases",
h->hashalg,
h->numsegs)));
return h;
}
