CODEWITHSUNDEEP
randomhash
meps
meps

Reputation: 579

Non-recursive pseudo-random number generation with discrete uniform distribution

I wonder is there any cheap and effective function to generate pseudo-random numbers by their indices? With something like that implementation:

var rand = new PseudoRandom(seed); // all sequences for same seeds are equal
trace(rand.get(index1)); // get int number by index1, for example =0x12345678
trace(rand.get(index2));
...
trace(rand.get(index1)); // must return the SAME number, =0x12345678

Probably it isn't about randomness but about good (fast and close as much as possible to uniform distribution) hashing where initial seed used as salt.

Upvotes: 0

Views: 240

Answers (1)

user515430
user515430

Reputation: 3351

You could build such random number generator out of the stream cipher Salsa20. One of the nice features of Salsa20 is that you can jump ahead to any offset very cheaply. And Salsa20 is fast, typically less than 20 cycles per byte. Since the cipher is indistinguishable from a truly random stream, uniformity should be excellent.

Since you probably don't need cryptographically secure random numbers, you could even reduce the number of rounds to something like 8 instead of the usual 20 rounds.

Another option is to just use the ideas behind Salsa20, how to mix up a state array (Bernstein calls that a hashing function), to build your own random number generator.

Upvotes: 2

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