Generate a sequence of unique random integers

random-sequence-of-unique.js

// Credit to Jeff Preshing
// https://preshing.com/20121224/how-to-generate-a-sequence-of-unique-random-integers/

class RandomSequenceOfUnique {
	constructor(intermediateOffset, seedBase=1) {
		this.index = permuteQPR(permuteQPR(seedBase) + 0x682f0161);
		this.intermediateOffset = intermediateOffset;
	}
	getNext() {
		const next = this.getNth(this.index);
		++this.index;
	}
	getNth(n) {
		// >>> ensures conversion to unsigned int
		return permuteQPR(((permuteQPR(n) + this.intermediateOffset) ^ 0x5bf03635) >>> 0);
	}
}

function permuteQPR(x) {
    const prime = 4294967291;
    const halfPrime = 2147483645;
    if (x >= prime)
        return x;  // The 5 integers out of range are mapped to themselves.

    // squaring can cause exceeding 2^53
    const residue = Number((BigInt(x) * BigInt(x)) % BigInt(prime));
    return (x <= halfPrime) ? residue : prime - residue;
}

// permuteQPR can be useful for generating some fancy intermediateOffset
module.exports = {RandomSequenceOfUnique, permuteQPR}