Given just four different values for the seed, how can you pick from 24,

I didn't say it could generate all those sequences. Only that from any given starting point, the non-repeating sequence could be any permutation of those 24 permutations.

Sure. But how many different such sequences can it make?

That's the wrong question. When generating the OPs 25-char sequences, you don't re-seed before starting each new sequence. You seed (implicitely) once and then follow that sequence until you have enough.

Therefore the upper bound is the length of the non-repeating sequence (the period) the prng can generate. (4.31e+6001 in the Mersenne Twister).

Of course, that is further constrained because of the modulo operation to bring the generated random values into the 0 .. 61 range. hence 6.45e44.

For the 15-bit RCPRNG built-in to perl on win32, the period (at least when seeded(1), seems (by experiment) to be 214741815.

Which looks suspiciously close to 2^31, but not quite.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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The start of some sanity?

In reply to Re^6: How likely is rand() to repeat? by BrowserUk
in thread How likely is rand() to repeat? by desertrat

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