String Hash function

hash.js

  //this uses a 32bit hash with a 1/100000 collison prob for a 300 string cache
  //this can has hash a 5k string 15000 per sec
  //so lets say about 500 messages per msec
  String.prototype.hashCode = function() {
    var hash = 0, i, chr, len;
    if (this.length == 0) return hash;
    for (i = 0, len = this.length; i < len; i++) {
      chr   = this.charCodeAt(i);
      hash  = ((hash << 5) - hash) + chr;
      hash = hash && hash; // hash |= 0; Convert to 32bit integer
    }
    return hash;
  };

We are not using the hash for security we are just using it to create a unique key for a given string.

The thing is that the although simple and fast the hash collision probability is really just too high to make a 32bit hash viable in almost all use cases.

MD5 creates a 128Bit hash which has a collision probability in the 100's of Trillions for our typical use case. iReal/FastMD5 has a very fast algorithm 240k ops per sec on the sort of string sizes we commonly use. So we can convert a complete module and template in around 2-3ms. Since this will only happen once a month and even then only on demand this is fast enough.

A comprehensive list of general purpose hash functions and their implementations can found here:

https://www.partow.net/programming/hashfunctions/index.html