Rockbox General > Rockbox General Discussion

what is "True random shuffle "

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riksweeney:

--- Quote from: RotAtoR on August 17, 2006, 05:22:03 PM ---It's general practice to seed it with the current (processor) clock tick, which for all devices so far is 1/100ths of seconds since rockbox was booted. A RTC is not necessary at all.

--- End quote ---

That's quite a cool idea, I was wondering how Rockbox did randomness on players without a clock.

ryran:
Ya know... am I the only one who would really love to have the option of a not-somuch-true-random, i.e. intelligent, shuffle? I love to create on-the-fly playlists of a handful to a dozen albums by different artists and have always thought it would be awesome if I could tell RB to shuffle the list in such a way that no two consecutive songs are from the same artist (or album).

That would rock. Perhaps I'll fill out a feature request.

soap:

--- Quote from: ryran on August 22, 2006, 10:45:43 AM ---Ya know... am I the only one who would really love to have the option of a not-somuch-true-random, i.e. intelligent, shuffle? I love to create on-the-fly playlists of a handful to a dozen albums by different artists and have always thought it would be awesome if I could tell RB to shuffle the list in such a way that no two consecutive songs are from the same artist (or album).

That would rock. Perhaps I'll fill out a feature request.

--- End quote ---

Foobar2000 has a pluggin (Shuffle) that does this in a very nice manner.  It allows you to set three variables.
1 - What percentage of the playlist to play before a repeat is allowed.
2 - What tag(s) to watch for when shuffling (example:  -album|+genre would shuffle to a different album, but same genre.  Leaving the field blank puts no restraint on the shuffle at all)
3 - A minimum and maximum distance from the last track the randomizer is allowed to jump.

Just thought I would throw that in there...

afruff23:
Actually no PRNG is actually random. Rockbox uses a Mersenne Twister(look in FAQ). Mersenne Twisters have a periodicity of  2^19937 − 1. Read
http://en.wikipedia.org/wiki/Mersenne_Twister
 for more info. After a while(a VERY LONG while), you will begin to notice repeating.

bk:
...where "a VERY LONG while" (if you change songs once per second) is a period of time many, many, many orders of magnitude greater than the age of the known universe.

Plug 2^19937 into a computer calculator with a sufficient output (bc on unix/linux works) to see how huge it is.

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