# [mythtv] MythMusic playlists still not intelligent enough IMHO

Eskil Heyn Olsen myth at eskil.org
Thu Apr 19 05:45:02 UTC 2007

```On Wed, 2007-04-18 at 10:50 -0400, Dan Wilga wrote:

> - choose the index of the first song, S, randomly:  S = rand() % N
> - afterward, each new song, S' is calculated like so:  S' = (S + P) % N
>
> A mathematics guru friend of mine sent me the proof that this
> sequence is guaranteed to visit each song exactly once, in a
> pseudorandom order. It also has the advantage that the sequence is

After looking at this, it seems that the pseudorandom order is just
continuously adding P % N to S and wrapping at N. So essentially, let N
be 50, P be 15485863 (big prime) and S0 be 20.

S1 = (20 + 15485863) % 50 = 33
S2 = (33 + 15485863) % 50 = 46
S3 = (46 + 15485863) % 50 = 9
S4 = (9 + 15485863) % 50 = 22

essentially you just add 13 (15485863 % 50) every time. That seems sub
pseudorandom to me. It even seems that the only reason you need a prime
is to ensure that P % N isn't 0.

Or did I (again) brainfart on something ?

eskil
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```