javascript將文字轉為數字hashcode

如同c# asp.net中的GetHashCode():

function getHashcode(msnid){
var hash = 0;
if (msnid.length == 0) return hash;
for (i = 0; i < msnid.length; i++) {
char = msnid.charCodeAt(i);
hash = ((hash<<5)-hash)+char;
hash = hash & hash; // Convert to 32bit integer
}
return hash;
}