# Hashing function and bloom filter

Refer to this example

http://billmill.org/bloomfilter-tutorial/

1) Using the 2 of the 9 hash functions you have, duplicate the process found in the above example.

2) Next create a file with random inputs and use all 9 hashes this time

http://pages.cs.wisc.edu/~cao/papers/summary-cache/node8.html

3) Choose several spots in the table with 9 hashes and confirm results with your program.

False Positive -> (1-e^(-km/n))^k where

n is the bit vector size

k are the number of hashes

m are the number of keys used in the hash to fill the vector.

code c++

HashTest.cpp

#include <iostream> //iostrem
#include <string>   //string
#include <vector>   //vector
#include “GeneralHashFunctions.h”

int main(int argc, char* argv[])
{
const std::string key = “abcdefghijklmnopqrstuvwxyz1234567890”;

std::cout << “General Purpose Hash Function Algorithms Test” << std::endl;
std::cout << “By Arash Partow – 2002        ” << std::endl;
std::cout << “Key: ”                          << key           << std::endl;
std::cout << ” 1. RS-Hash Function Value:   ” << RSHash (key) << std::endl;
std::cout << ” 2. JS-Hash Function Value:   ” << JSHash (key) << std::endl;
std::cout << ” 3. PJW-Hash Function Value: ” << PJWHash (key) << std::endl;
std::cout << ” 4. ELF-Hash Function Value: ” << ELFHash (key) << std::endl;
std::cout << ” 5. BKDR-Hash Function Value: ” << BKDRHash(key) << std::endl;
std::cout << ” 6. SDBM-Hash Function Value: ” << SDBMHash(key) << std::endl;
std::cout << ” 7. DJB-Hash Function Value: ” << DJBHash (key) << std::endl;
std::cout << ” 8. DEK-Hash Function Value: ” << DEKHash (key) << std::endl;
std::cout << ” 9. FNV-Hash Function Value: ” << FNVHash (key) << std::endl;
std::cout << “10. BP-Hash Function Value:   ” << BPHash (key) << std::endl;
std::cout << “11. AP-Hash Function Value:   ” << APHash (key) << std::endl;

return 1;
}

GeneralHashFunctions.cpp

#include “GeneralHashFunctions.h”

unsigned int RSHash(const std::string& str)
{
unsigned int b    = 378551;
unsigned int a    = 63689;
unsigned int hash = 0;

for(std::size_t i = 0; i < str.length(); i++)
{
hash = hash * a + str[i];
a    = a * b;
}

return hash;
}
/* End Of RS Hash Function */

unsigned int JSHash(const std::string& str)
{
unsigned int hash = 1315423911;

for(std::size_t i = 0; i < str.length(); i++)
{
hash ^= ((hash << 5) + str[i] + (hash >> 2));
}

return hash;
}
/* End Of JS Hash Function */

unsigned int PJWHash(const std::string& str)
{
unsigned int BitsInUnsignedInt = (unsigned int)(sizeof(unsigned int) * 8);
unsigned int ThreeQuarters     = (unsigned int)((BitsInUnsignedInt * 3) / 4);
unsigned int OneEighth         = (unsigned int)(BitsInUnsignedInt / 8);
unsigned int HighBits          = (unsigned int)(0xFFFFFFFF) << (BitsInUnsignedInt – OneEighth);
unsigned int hash              = 0;
unsigned int test              = 0;

for(std::size_t i = 0; i < str.length(); i++)
{
hash = (hash << OneEighth) + str[i];

if((test = hash & HighBits) != 0)
{
hash = (( hash ^ (test >> ThreeQuarters)) & (~HighBits));
}
}

return hash;
}
/* End Of P. J. Weinberger Hash Function */

unsigned int ELFHash(const std::string& str)
{
unsigned int hash = 0;
unsigned int x    = 0;

for(std::size_t i = 0; i < str.length(); i++)
{
hash = (hash << 4) + str[i];
if((x = hash & 0xF0000000L) != 0)
{
hash ^= (x >> 24);
}
hash &= ~x;
}

return hash;
}
/* End Of ELF Hash Function */

unsigned int BKDRHash(const std::string& str)
{
unsigned int seed = 131; // 31 131 1313 13131 131313 etc..
unsigned int hash = 0;

for(std::size_t i = 0; i < str.length(); i++)
{
hash = (hash * seed) + str[i];
}

return hash;
}
/* End Of BKDR Hash Function */

unsigned int SDBMHash(const std::string& str)
{
unsigned int hash = 0;

for(std::size_t i = 0; i < str.length(); i++)
{
hash = str[i] + (hash << 6) + (hash << 16) – hash;
}

return hash;
}
/* End Of SDBM Hash Function */

unsigned int DJBHash(const std::string& str)
{
unsigned int hash = 5381;

for(std::size_t i = 0; i < str.length(); i++)
{
hash = ((hash << 5) + hash) + str[i];
}

return hash;
}
/* End Of DJB Hash Function */

unsigned int DEKHash(const std::string& str)
{
unsigned int hash = static_cast(str.length());

for(std::size_t i = 0; i < str.length(); i++)
{
hash = ((hash << 5) ^ (hash >> 27)) ^ str[i];
}

return hash;
}
/* End Of DEK Hash Function */

unsigned int BPHash(const std::string& str)
{
unsigned int hash = 0;
for(std::size_t i = 0; i < str.length(); i++)
{
hash = hash << 7 ^ str[i];
}

return hash;
}
/* End Of BP Hash Function */

unsigned int FNVHash(const std::string& str)
{
const unsigned int fnv_prime = 0x811C9DC5;
unsigned int hash = 0;
for(std::size_t i = 0; i < str.length(); i++)
{
hash *= fnv_prime;
hash ^= str[i];
}

return hash;
}
/* End Of FNV Hash Function */

unsigned int APHash(const std::string& str)
{
unsigned int hash = 0xAAAAAAAA;

for(std::size_t i = 0; i < str.length(); i++)
{
hash ^= ((i & 1) == 0) ? ( (hash << 7) ^ str[i] * (hash >> 3)) :
(~((hash << 11) + (str[i] ^ (hash >> 5))));
}

return hash;
}
/* End Of AP Hash Function */

GeneralHashFunctions.h

#ifndef INCLUDE_GENERALHASHFUNCTION_CPP_H
#define INCLUDE_GENERALHASHFUNCTION_CPP_H

#include

typedef unsigned int (*HashFunction)(const std::string&);

unsigned int RSHash (const std::string& str);
unsigned int JSHash (const std::string& str);
unsigned int PJWHash (const std::string& str);
unsigned int ELFHash (const std::string& str);
unsigned int BKDRHash(const std::string& str);
unsigned int SDBMHash(const std::string& str);
unsigned int DJBHash (const std::string& str);
unsigned int DEKHash (const std::string& str);
unsigned int BPHash (const std::string& str);
unsigned int FNVHash (const std::string& str);
unsigned int APHash (const std::string& str);

#endif

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