README

xx-prng

A seeded 32 bit counter prng based on the xxHash algorithm.

This is designed for procedural art or games where you may need to save or resume state from a different point in a render or level generation.

Usage

Generate seeded random functions

import seeded from 'xx-prng/lib/seeded.js';

import uint from 'xx-prng/lib/transforms/uint.js';
import range from 'xx-prng/lib/transforms/range.js';
import list from 'xx-prng/lib/transforms/list.js';

const { random } = seeded(12345);

// Default is a Math.random() like float in the range [0.0,1.0)
random();

// Random float in the range [0.0,1.0]
random(range(0,1));

// Random float in the range [0.0,5.0]
random(range(5));

// Random float in the range [5.0,15.0]
random(range(5,15));

// Random 32 bit integer the range [0,0xffffffff]
random(uint())

// Random list of 5 floats
random(list(5));

// Random list of 3 uints
random(list(3,uint()));

Saving & Loading Counter State

import seeded from 'xx-prng/lib/seeded.js';

const A = seeded(123);
A.random();
A.random();

// Create a new instance from same seed and A's current counter
const B = seeded(123, A.state());

A.random() == B.random()

// Set state
A.state(10)
B.state(10)
A.random() = B.random()

Internal Hash Functions

You can use the internal hash functions directly with your own state or counters...

import hash from 'xx-prng/lib/hash.js';
import hash0 from 'xx-prng/lib/hash0.js';
import hash1 from 'xx-prng/lib/hash1.js';
import hash2 from 'xx-prng/lib/hash2.js';
import hash3 from 'xx-prng/lib/hash3.js';

const levelSeed = 12345;
const level = Array.from(Array(100), () => new Array(100));

// Generate random 32 bit integers from multiple counters
for(let x = 0 ; x < 100; x++) {
  for(let y = 0 ; y < 100; y++) {
    // Random 32 bit integer from seed + 2 counters
    level[x][y] = hash2(levelSeed, x,y);
  }
}

// Generate random 32 bit integer from a single seed
let s = hash0(123);

// Generate random 32 bit integer from a seed and a counter
let s1 = hash1(123,1);

// Generate random 32 bit integer from a seed and a list of integers
let s7 = hash(123,[1,2,3,4,5,6,7]);

// Hash of arrays of integers are equal to named functions but slower
hash3(123,1,2,3) == hash(123,[1,2,3]);