How to create a fast pseudo-random hashCode?

Question

I am working on a Java to WebAssembly compiler (JWebAssembly). I need to replace native code with things that can run in WebAssembly.

For java.lang.Object.hashCode() and java.lang.System.identityHashCode() I use currently the follow JavaScript code:

identityHashCode = (o) => {
  var h = o[1];
  while( h == 0 ){
    o[1] = h = Math.round( ( Math.random() - 0.5 ) * 0xffff );
  }
  return h;
}

But this required for every new hashCode a round trip to the JavaScript scope which cost performance. With a browserless environment (without JavaScript) like WASI this will not work. That I search for a poor replacement.

I think a hashCode:

• does not need be really random
• the values must only be well distributed

Is this correct?

The follow Java code should be good enough.

private static int globalHash = (int)System.currentTimeMillis();

private int hashCode;
public int hashCode() {
  if( hashCode == 0 ) {
    hashCode = globalHash = (globalHash + 1) * 31; 
  }
  return hashCode;
}

Is this good enough for a generic hashCode function? Would there a better implementation?