Random generator

[Trythat]

This might seem a stupid question but here goes -

I wrote a key generator for one of my programs in Visual Basic, so I recieve
sales notification via email and then use my program to generate the key and
send it via Email.

Well after finding out about PHP, and that my host does PHP, I thought it would
be quicker and more reliable to generate the keys on the server and send them
out again either vai email or from the sales site.

So I wrote the generator in PHP and surprisingly it works, or rather it works
in a half assed fashion, I can generate keys, but they are not the same as the
ones generated by my VB program.

And here is my problem, I suspect its becuase I'm using a randomised Seed, and
I'm thinking that VB and PHP Randomisers are not compatable.

Am I right in my thoughts and if so, is there a way around it?
Is the only answer not to use a randomiser? or how do people generate keys from
the server when using other languages ie C++ etc?

TIA

[Garp]

Re: Random generator


"Trythat" <don't@bother.o rg> wrote in message
news:4qll70du7a qnuqr9p5rio1qse c1l7ht2pv@4ax.c om...[color=blue]
> This might seem a stupid question but here goes -
>
> I wrote a key generator for one of my programs in Visual Basic, so I[/color]
recieve[color=blue]
> sales notification via email and then use my program to generate the key[/color]
and[color=blue]
> send it via Email.[/color]
<snip>[color=blue]
> And here is my problem, I suspect its becuase I'm using a randomised Seed,[/color]
and[color=blue]
> I'm thinking that VB and PHP Randomisers are not compatable.[/color]

I should hope so.

If you truly want the same number from the same seed, use the same algorithm
in both.

Try this one in both:
(return x= (x*1103515245UL +12345UL)&0x7ff fffff);


Garp

[Trythat]

Re: Random generator

On Mon, 12 Apr 2004 19:01:19 GMT, "Garp" <garp7@no7.blue yonder.co.uk> wrote:
[color=blue]
>
>"Trythat" <don't@bother.o rg> wrote in message
>news:4qll70du7 aqnuqr9p5rio1qs ec1l7ht2pv@4ax. com...[color=green]
>> This might seem a stupid question but here goes -
>>
>> I wrote a key generator for one of my programs in Visual Basic, so I[/color]
>recieve[color=green]
>> sales notification via email and then use my program to generate the key[/color]
>and[color=green]
>> send it via Email.[/color]
><snip>[color=green]
>> And here is my problem, I suspect its becuase I'm using a randomised Seed,[/color]
>and[color=green]
>> I'm thinking that VB and PHP Randomisers are not compatable.[/color]
>
>I should hope so.
>
>If you truly want the same number from the same seed, use the same algorithm
>in both.
>
>Try this one in both:
>(return x= (x*1103515245UL +12345UL)&0x7ff fffff);
>[/color]

I am using the same algorithm, but using Random and as you say, they generate
the random numbers differently, I've not time to now to try out your answer
above, but what does it actually mean?

They way I understood the VB and PHP randomiser for that matter, is that if I
seed them, I will get a random number each time but its a psudo random number,
in so much as each time I call it the random numbers are repeatable.

But thinking about it, perhaps they're not as random as I thought, as I only
run the program each time I get a registration, and the seed is always the
same.

This mathamatics is making making my head hurt, I think I'm going to bed and
try and think this out a bit more.

Thanks for your help though, if you've anything more to add, I'll take it with
open arms.

[Chung Leong]

Re: Random generator

"Trythat" <don't@bother.o rg> wrote in message
news:nn4m70th9m p24bo3pedrii1oj eqfr4ha78@4ax.c om...[color=blue]
> On Mon, 12 Apr 2004 19:01:19 GMT, "Garp" <garp7@no7.blue yonder.co.uk>[/color]
wrote:[color=blue]
>
> I am using the same algorithm, but using Random and as you say, they[/color]
generate[color=blue]
> the random numbers differently, I've not time to now to try out your[/color]
answer[color=blue]
> above, but what does it actually mean?
>
> They way I understood the VB and PHP randomiser for that matter, is that[/color]
if I[color=blue]
> seed them, I will get a random number each time but its a psudo random[/color]
number,[color=blue]
> in so much as each time I call it the random numbers are repeatable.[/color]

How do you know you're using the same pseudo-random algorithm? The rand
function in PHP uses the C rand function, which may differ from C library to
C library.

[Garp]

Re: Random generator


"Chung Leong" <chernyshevsky@ hotmail.com> wrote in message
news:nLmdnQ20oe-AvObdRVn-vw@comcast.com. ..[color=blue]
> "Trythat" <don't@bother.o rg> wrote in message
> news:nn4m70th9m p24bo3pedrii1oj eqfr4ha78@4ax.c om...[color=green]
> > On Mon, 12 Apr 2004 19:01:19 GMT, "Garp" <garp7@no7.blue yonder.co.uk>[/color]
> wrote:[color=green]
> >
> > I am using the same algorithm, but using Random and as you say, they[/color]
> generate[color=green]
> > the random numbers differently, I've not time to now to try out your[/color]
> answer[color=green]
> > above, but what does it actually mean?
> >
> > They way I understood the VB and PHP randomiser for that matter, is that[/color]
> if I[color=green]
> > seed them, I will get a random number each time but its a psudo random[/color]
> number,[color=green]
> > in so much as each time I call it the random numbers are repeatable.[/color]
>
> How do you know you're using the same pseudo-random algorithm? The rand
> function in PHP uses the C rand function, which may differ from C library[/color]
to[color=blue]
> C library.[/color]

Almost certainly.

What the PRNG system does is calculate a seemingly random number based on a
seed value, using an algorithm like the one I posted above. That will
produce a predictable sequence from known seeds, but seed it from time() and
it will be as random as you need.

What I'm suggesting to the OP is that he doesn't rely on the built-ins
because he's getting different results - so use a consistent algorithm on
both. He could then store the seed in the database and get the same value
from both systems, which is what he wanted.

Garp

[Trythat]

Re: Random generator

On Mon, 12 Apr 2004 23:33:22 GMT, "Garp" <garp7@no7.blue yonder.co.uk> wrote:
[color=blue]
>
>"Chung Leong" <chernyshevsky@ hotmail.com> wrote in message
>news:nLmdnQ20o e-AvObdRVn-vw@comcast.com. ..[color=green]
>> "Trythat" <don't@bother.o rg> wrote in message
>> news:nn4m70th9m p24bo3pedrii1oj eqfr4ha78@4ax.c om...[color=darkred]
>> > On Mon, 12 Apr 2004 19:01:19 GMT, "Garp" <garp7@no7.blue yonder.co.uk>[/color]
>> wrote:[color=darkred]
>> >
>> > I am using the same algorithm, but using Random and as you say, they[/color]
>> generate[color=darkred]
>> > the random numbers differently, I've not time to now to try out your[/color]
>> answer[color=darkred]
>> > above, but what does it actually mean?
>> >
>> > They way I understood the VB and PHP randomiser for that matter, is that[/color]
>> if I[color=darkred]
>> > seed them, I will get a random number each time but its a psudo random[/color]
>> number,[color=darkred]
>> > in so much as each time I call it the random numbers are repeatable.[/color]
>>
>> How do you know you're using the same pseudo-random algorithm? The rand
>> function in PHP uses the C rand function, which may differ from C library[/color]
>to[color=green]
>> C library.[/color]
>
>Almost certainly.
>
>What the PRNG system does is calculate a seemingly random number based on a
>seed value, using an algorithm like the one I posted above. That will
>produce a predictable sequence from known seeds, but seed it from time() and
>it will be as random as you need.
>
>What I'm suggesting to the OP is that he doesn't rely on the built-ins
>because he's getting different results - so use a consistent algorithm on
>both. He could then store the seed in the database and get the same value
>from both systems, which is what he wanted.[/color]

Thank you both for your help, I think for the time being I'm going to leave
this one program as it is.

But I plan on converting the main program to Java and running it on the Palm
and Pocket PC, so I can use basicly the same routine but without using Random
from either Java or PHP.

Garp is there a page I can find out a bit more info about the algorithm you
posted, as I really didn't understand it :(?

[Sandman]

Re: Random generator

In article <6HFec.2251$i67 .22112301@news-text.cableinet. net>, "Garp"
<garp7@no7.blue yonder.co.uk> wrote:
[color=blue][color=green][color=darkred]
>>> I am using the same algorithm, but using Random and as you say, they
>>> generate the random numbers differently, I've not time to now to try
>>> out your answer above, but what does it actually mean?
>>>
>>> They way I understood the VB and PHP randomiser for that matter, is
>>> that if I seed them, I will get a random number each time but its a
>>> psudo random number, in so much as each time I call it the random
>>> numbers are repeatable.[/color]
>>
>> How do you know you're using the same pseudo-random algorithm? The
>> rand function in PHP uses the C rand function, which may differ from
>> C library to C library.[/color]
>
> Almost certainly.
>
> What the PRNG system does is calculate a seemingly random number based
> on a seed value, using an algorithm like the one I posted above. That
> will produce a predictable sequence from known seeds, but seed it from
> time() and it will be as random as you need.[/color]

I suggest using microtime() instead, if you may want to access a random value
more than once in a second.



function getmicrotime(){
list($usec, $sec) = explode(" ",microtime ());
return ((float)$usec + (float)$sec);
}

--
Sandman[.net]