Common hash functions

Principles refer to "Introduction to Algorithms"

One, the division hash function

 

Implement the algorithm according to the description, first take the corresponding seed

int hash_mod_seed( int n, int iCheck) { // Store n keywords, an unsuccessful search needs to check iCheck keywords, the default one character is 8 bits 
    int iStart= n / iCheck, prime = (iStart == 1 ) ? 2 : iStart;
    assert(iCheck >= 0 && iCheck <= 8 );
     // The odd start should skip the already judged odd number 
    for ( int j = 0 , odd = (iStart % 2 == 0 ) ? iStart / 2 : (iStart - 1 ) / 2 + 1 ;
        j < 8 - iCheck; odd++ ) {
         // generate a prime number 
        bool fPrime = true ;
         for ( int k = 2 ; k <= sqrt(prime); k++ )
             if (prime % k == 0 ) {
                fPrime = false;
                break;
            }
        if (fPrime) // Record the prime number 
            j++ ;
        prime = odd * 2 + 1 ; // odd number to be determined 
    }
     return prime - 2 ;
}

Key Algorithm Implementation

int hash_mod(int key, int seed) {
    return key % seed;
}

2. Multiplicative Hash Function

Implemented according to the algorithm description

int hash_mul( int key, int w, int p) { // w means that the keyword int is 32 bits, and p is the most significant bit truncated after mapping 
    __int64 s = (sqrt( 5 ) - 1 ) / 2 * pow( 2 , w);
    __int64 r0 = s*key % ( int )pow( 2 , w);
     return r0 / pow( 2 , w - p); // high p significant bits 
}

 

All code is tested and the result is correct