0
193
VistasConvert strings to 16Bit UTF integers in Javascript
I'm working with firebase firestore and for some reason I need to hash every new user document ID to integer specifically a 16Bit UTF integer. Mostly it's an attempt at duplicating the .hashcode method in Dart.
what I have found and tried is this
// Convert to 32bit integer
const hashFunction = (string) => {
var hash = 0;
if (string.length == 0) return hash;
for (i = 0; i < string.length; i++) {
char = string.charCodeAt(i);
hash = (hash << 5) - hash + char;
hash = hash & hash;
}
return hash >>> 0; // returns hash as positive integer
};
but this only converts to 32bit int. Any and all help is appreciated.
EDIT1: Using @selbie's changes i made some progress but the hash i'm getting is quite different from the .hashCode method in Dart
and 
is there anyway i can get thesame result
1 Respuestas
Responde la pregunta0
If you only want a 16-bit hash, then:
Instead of this:
return hash >>> 0; // returns hash as positive integer
This:
return hash & 0xffff; // return lower 16-bits of hash value
This line:
if (string.length == 0) return hash;
Isn't needed since your for-loop will simply not run if string.length is 0.
Finally, not a good idea to have a variable name the same as a type. So let's just rename string to be s.
Here's a simplified solution:
const hashFunction = (s) => {
var hash = 0;
for (i = 0; i < s.length; i++) {
hash = (hash << 5) - hash + s.charCodeAt(i);
hash = hash & hash; // prevent overflow from happening
}
return hash & 0xffff; // returns lower 16-bit of hash value
};
With that in mind, a 16-bit hash isn't a very strong hash. There are sure to be collisions after a few thousand strings are hashed. Consider a crytographically strong hash or a larger hash width as appropriate.