Martijn Apparently PHP does not ensure backwards compatibility for their Mersenne Twister implementation. In other words: if you depend on predictable pseudo-randomness you might want to roll your own implementation. That's just silly.

Mark Dain When would you depend on predictable random number generators in that way?

Martijn When results must be verifiable. Most Monte Carlo simulations use a seeded PRNG so other people can test and re-run them to validate the results. Many of today's video games make use of a seeded PRNG as well, e.g. The Binding of Isaac offers randomly generated dungeons but also shows you their seed values for easy sharing amongst players. Mersenne Twister was never cryptographically secure, it was just relatively fast, very fit for seeded pseudo-randomness. And PHP choose to break backwards compatibility.

Mark Dain PHP sucks in general. But thanks for the explanation, now it hits me how Minecraft's level generator works (you share the seed for the PRNG).