@Fred: Questions about RandomSeed(), Random()

[Hades]

Hi Fred.

1. What values make sense for RandomSeed() ? (0..2^31-1 ?)

2. What is the highest useful value for Random() ? (2^31-1 ?)

3. Any hint what kind of PRNG you are using?


Have a nice day,

Hades

[Hades]

Still no answer...

[Comtois]

1. What values make sense for RandomSeed() ? (0..2^31-1 ?)

RandomSeed(ElapsedMilliseconds()) or use a long.

2. What is the highest useful value for Random() ? (2^31-1 ?)

$7FFFFFFF or +2147483647 (it's a signed long)

[Trond]

Random() takes any number from 0 to 2147483647. (Quads are truncated.)
RandomSeed() takes any number from -2147483648 to 2147483647. I don't know whether it actually uses the entire range.

[Hades]

Thank you for your answers.

to RandomSeed():
I have to be sure I can use at least 30 bit for the seed, and they are fully used by the PRNG (produce different, repeatable results). Does anybody know if that is the case?

[Trond]

Thank you for your answers.

to RandomSeed():
I have to be sure I can use at least 30 bit for the seed, and they are fully used by the PRNG (produce different, repeatable results). Does anybody know if that is the case?

If that is not the case it sounds like a bug, but you can always test it.

[Dare2]

This ..

Code: Select all

RandomSeed(%111111111111111111111111111111)
For i = 1 To 20
  Debug Random($7FFFFFFF)
Next

Always gives me this ..

• 1428841689
  1400720876
  2101687175
  1376130085
  509981955
  1786875312
  1012963906
  743527194
  1792047849
  1862237268
  1854146918
  1918186864
  634768099
  2090250383
  243859415
  814637835
  2055386557
  230076762
  681308473
  415508342

And this..

Code: Select all

RandomSeed(%101010101010101010101010101010)
For i = 1 To 20
  Debug Random($7FFFFFFF)
Next

Always gives me this..

• 694093175
  733968713
  375167596
  360530968
  1269931708
  162140230
  1154304316
  127478278
  734274873
  904269346
  496657588
  969237289
  142867284
  1356160719
  830562000
  1422205369
  1447137896
  40352398
  520117975
  282751248

[Hades]

@Trond

No, it wouldn't be a bug, just a weak random number generator.
And if it's a good generator it isn't that easy to test.
The easiest way would be an answer of Fred. He should know.

@Dare2

Ok, but how do I know that there aren't other seeds, that give the same numbers?

[Trond]

I didn't say it was easy to test if it was good, only if it produces repeatable results.

[Dare2]

@Dare2

Ok, but how do I know that there aren't other seeds, that give the same numbers?

Only thought I have on that is looping from min to max random seed and getting the first few results from each. Store results, look for duplicates, if there are dupes, use these in a smaller test with a larger sample.

Not too trivial a file size, though. But it would resolve your question for you.

[Hades]

Oh no, thanks. I don't want to kill your CPU.

Would be easier just to implement a Mersenne Twister.

[Dare2]

Oh no, thanks. I don't want to kill your CPU.

Actually, I was rather thinking of it happening on your gear.

[Hades]

I thought you said :
'Not too trivial a file size, though. But I would resolve your question for you.'

Now I see you said 'it'.

[Dare2]

[josku_x]

PS: though is different than thought. You got a typo or I am blind.

EDIT: @Dare2: Grrrrrrrrr!!!!!