1. // This snippet compares two PRNG algorithms using the incremental seed test
  3. // "Small Fast Counter 32"
  4. // This is a good algorithm from the PractRand test suite: http://pracrand.sourceforge.net/RNG_engines.txt
  5. // It passes stringent randomness tests (PractRand, TestU01).
  7. function sfc32(a, b, c, d) {
  8. return function() {
  9. a >>>= 0; b >>>= 0; c >>>= 0; d >>>= 0;
  10. var t = (a + b) | 0;
  11. a = b ^ b >>> 9;
  12. b = c + (c << 3) | 0;
  13. c = (c << 21 | c >>> 11);
  14. d = d + 1 | 0;
  15. t = t + d | 0;
  16. c = c + t | 0;
  17. return (t >>> 0) / 4294967296;
  18. }
  19. }
  21. // MWC1616, as used in Chrome's Math.random() circa 2015
  22. // This is NOT a good algorithm: https://medium.com/@betable/tifu-by-using-math-random-f1c308c4fd9d#.7p3lk9bvk
  23. // It fails stringent randomness tests.
  25. function mwc(a, b) {
  26. return function() {
  27. a = 36969 * (a & 65535) + (a >>> 16);
  28. b = 18000 * (b & 65535) + (b >>> 16);
  29. var result = (a << 16) + (b & 65535) >>> 0;
  30. return result / 4294967296;
  31. }
  32. }
  34. // Which one passes the seed test?
  36. let count = 0; setInterval(() => {
  37. console.log(
  38. Math.round(sfc32(count++,count++,count++,count++)()*100),
  39. Math.round(mwc(count++,count++)()*100),
  40. );
  41. }, 500);