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Full Discussion: Hash Function Speed
Top Forums Programming Hash Function Speed Post 302364017 by killerqb on Wednesday 21st of October 2009 11:14:23 PM
Old 10-22-2009
Hash Function Speed

I have created my own hash table class, but am looking to speed it up. My current hash function is:

Code:
 int HashTable::hashFunc(const string &key) const
        {
		int tableSize = theLists.size();
            int hashVal = 0;
			for(int i = 0; i<key.length();  i++)
			hashVal = 37*hashVal+key[i];
			hashVal %= tableSize;
			if(hashVal<0)
			hashVal += tableSize;
			return hashVal;
        }

I am looking for an alternative function that can hash a string. That will probably yield similar results.
 

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Tie::SubstrHash(3pm)					 Perl Programmers Reference Guide				      Tie::SubstrHash(3pm)

NAME
Tie::SubstrHash - Fixed-table-size, fixed-key-length hashing SYNOPSIS
require Tie::SubstrHash; tie %myhash, 'Tie::SubstrHash', $key_len, $value_len, $table_size; DESCRIPTION
The Tie::SubstrHash package provides a hash-table-like interface to an array of determinate size, with constant key size and record size. Upon tying a new hash to this package, the developer must specify the size of the keys that will be used, the size of the value fields that the keys will index, and the size of the overall table (in terms of key-value pairs, not size in hard memory). These values will not change for the duration of the tied hash. The newly-allocated hash table may now have data stored and retrieved. Efforts to store more than $table_size elements will result in a fatal error, as will efforts to store a value not exactly $value_len characters in length, or reference through a key not exactly $key_len characters in length. While these constraints may seem excessive, the result is a hash table using much less internal memory than an equivalent freely-allocated hash table. CAVEATS
Because the current implementation uses the table and key sizes for the hashing algorithm, there is no means by which to dynamically change the value of any of the initialization parameters. The hash does not support exists(). perl v5.16.3 2013-02-26 Tie::SubstrHash(3pm)
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