Javascript geohash implementation

gistfile1.js

Array.prototype.average = function() {
	var i, len, sum = 0;

	for (i=0, len=this.length; i<len; i++) {
		sum += this[i];
	}
	
	return sum / this.length;
};

GeoHash = {
	'generate' : function(latitude, longitude, geohashLength) {
		
	}, 'decode' : function(hash) {
		var i, j, len, symbol, index, tmp, interval,
			binaryValue = '',
			latitudeBinary = '',
			longitudeBinary = '',
			lat = 0,
			lng = 0,
			base32 = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "b", "c", "d", "e", "f", "g", "h", "j", "k", "m", "n", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"];
		
		for (i=0, len=hash.length; i<len; i++) {
			symbol = hash.substr(i, 1);
			index = base32.indexOf(symbol);
			
			if (index === -1) {
				return false;
			}
			
			tmp = index.toString(2);
			if (tmp.length < 5 ) {
				for (j=tmp.length; j<5; j++) {
					tmp = '0' + tmp;
				}
			}
			
			binaryValue += tmp;
		}
		
		for (i=0, len=binaryValue.length; i<len; i++) {
			if (i%2 === 0) {
				longitudeBinary += binaryValue.substr(i, 1);
			} else {
				latitudeBinary += binaryValue.substr(i, 1);
			}
		}
		
		// calculate latitude
		interval = [-90, 90];
		for (i=0, len=latitudeBinary.length; i<len; i++) {
			tmp = parseInt(latitudeBinary.substr(i, 1), 10);
			if (tmp === 1) {
				interval[0] = interval.average();
			} else {
				interval[1] = interval.average();
			}
			
			lat = interval.average();
		}
		
		// calculate longitude
		interval = [-180, 180];
		for (i=0, len=longitudeBinary.length; i<len; i++) {
			tmp = parseInt(longitudeBinary.substr(i, 1), 10);
			if (tmp === 1) {
				interval[0] = interval.average();
			} else {
				interval[1] = interval.average();
			}
			
			lng = interval.average();
		}
		
		return [lat, lng];
	}
};