51–56 of 56 posts
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Fisher-Yates is one of the simplest things out there IMO. Isn't the Lehmer code the thing that you want? Then you can specify your permutation with an integer and extract the individual digits from it repeatedly.
Fisher-Yates is one of the simplest things out there IMO Just using "$n xor $something" would be simpler. I am just not sure yet, what a good "$something" is.
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Wouldn't a SIMDified implementation of other RNGs speed them up by a comparable factor, making MT relatively slower again?
If the next number depends on the previous number (like with wyrand and many others) it can't be simdified. You could simdify computation with different seeds tho, which might be fine for many purposes. However at that point it's also a custom implementation with a different number sequence than the non-simd version, which isn't the case with a SIMDified MT.
https://nullprogram.com/blog/2018/07/31/
Out of curiosity, is running the state through a hash a reasonable rand strategy?
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Xoring won’t work: - xoring will only produce permutations that have period two, and every element will be part of a 2-cycle. - if your n isn’t a power of two, it may produce numbers larger than n The set of 2-cycles will have a lot of structure, too (for example, if your magic constant is even, all cycles will have either two even numbers or two odd numbers; if it is odd, all cycles will have an even and an odd numb…
if your n isn’t a power of two, it may produce numbers larger than n This is the biggest problem. The others are not such big problems as I don't need strong resemblence to real randomness.
For example, it will still alternate odd and even numbers.
Also, an adversary can derive the xor key from a single sample, and predict the entire sequence from it.
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if your n isn’t a power of two, it may produce numbers larger than n This is the biggest problem. The others are not such big problems as I don't need strong resemblence to real randomness.
I can’t look into your use case, but I’m not sure you realize how spectacularly bad xoring with a fixed value is as a way to generate a ‘random’ permutation. For example, it will still alternate odd and even numbers. Also, an adversary can derive the xor key from a single sample, and predict the entire sequence from it.
There is no adversary. The use case is not about security.