i8 pwr = 0x400; // start with 1024
int diff=2<<30;
for(int i=0; i < 32; i++)
{
pwr<<=1;
if(pwr > base) {
break;
} else {
diff = base - pwr;
}
}
if( (pwr - base) > diff) {
// use previous pwr
pwr >>=1;
}
i8 p2 = w_findprime(pwr);
if(debug) {
cout
<< "base " << base
<< " closest power of 2 " << pwr
<< " findprime -> " << p2
<< endl;
}
if(printpower) cout << pwr << endl;
if(printprime) cout << p2 << endl;
// i8 p1 = w_findprime(base);
// Work backward from p1 to bpool size to request.
i8 nbufpages = ((p2 * 9)-8)/16 ;
void testit() {
::srand (4344); // for repeatability
for (int i = 0; i < HASH_COUNT; ++i) {
_hash_seeds[i] = ((uint32_t) ::rand() << 16) + ::rand();
}
cout << "tries=" << tries << endl;
dump();
#define page_sz 8192ull
int64_t nbufpages=(_size * 1024 - 1)/page_sz + 1; // sm.cpp passes to
// bf_m constructor
int64_t nbuckets=(16*nbufpages+8)/9; // bf_core_m constructor
int64_t _prime = w_findprime(int64_t(nbuckets));
if(!use_prime) { // override
_prime = _prime_replacement;
}
cout << "For requested bp size "<< _size << ": "
<< endl
<< "\t nbufpages=" << nbufpages << " of page size " << page_sz << ","
<< endl
<< "\t nbuckets (from bf_core_m constructor)=" << nbuckets << ","
<< endl;
if(use_prime) {
cout << "\t use prime " ;
}
cout
<< " _size=" << _prime
<< endl;
_size = _prime;
int *buckets = new int[_size];
for(int i=0; i < _size; i++)
{ buckets[i]=0; }
for(int i=0; i < tries; i++)
{
#define START 0
int j= START + i;
bfpid_t p(1,5,j);
for (int k=0; k < hash_count; k++)
{
unsigned h=::hash(k,p);
if(prnt) {
cout << ::hex << "0x" << h << ::dec
<< " \t " << p
<< " hash # " << k ;
if(buckets[int(h)] > 0) cout << " XXXXXXXXXXXXXXXXXXXX ";
cout << endl;
}
buckets[int(h)]++;
}
}
int worst=0;
int ttl=0;
for(int i=0; i < _size; i++)
{
int collisions=buckets[i]-1;
if(collisions > 0) {
ttl += collisions;
if(collisions > worst) worst=collisions;
}
}
cout << "SUMMARY: buckets: " << _size
<< endl
<< " tries: " << tries << "(x " << hash_count
<< " hashes=" << tries*hash_count << "); "
<< endl
<< " collisions: " << ttl
<< " ( " << 100*float(ttl)/float(tries*hash_count) << " %) "
<< endl
<< " worst case (max bkt len): " << worst
<< endl;
delete[] buckets;
}
