48-bit bitwise operations in Javascript?

Question

I've been given the task of porting Java's Java.util.Random() to JavaScript, and I've run across a huge performance hit/inaccuracy using bitwise operators in Javascript on sufficiently large numbers. Some cursory research states that "bitwise operators in JavaScript are inherently slow," because internally it appears that JavaScript will cast all of its double values into signed 32-bit integers to do the bitwise operations (see here for more on this.) Because of this, I can't do a direct port of the Java random number generator, and I need to get the same numeric results as Java.util.Random(). Writing something like

  this.next = function(bits) {
    if (!bits) {
       bits = 48;
    }
    this.seed = (this.seed * 25214903917 + 11) & ((1 << 48) - 1);
    return this.seed >>> (48 - bits);
  };

(which is an almost-direct port of the Java.util.Random()) code won't work properly, since Javascript can't do bitwise operations on an integer that size.)

I've figured out that I can just make a seedable random number generator in 32-bit space using the Lehmer algorithm, but the trick is that I need to get the same values as I would with Java.util.Random(). What should I do to make a faster, functional port?

Answer 1

Instead of foo & ((1 << 48) - 1) you should be able to use foo % Math.pow(2,48).

All numbers in Javascript are 64-bit floating point numbers, which is sufficient to represent any 48-bit integer.