OpenEuphoria

Re: 32-bit random numbers

• Posted by "Juergen Luethje" <j.lue at gmx.de> Jul 05, 2004
• 579 views

Me wrote:

> Derek Parnell wrote:
>
> [snipped old text]
>
>> Maybe this will be useful...
>>
>> -- rand32.e
>> -- Produces a pseudo-random integer between 1 and N
>>
>> include machine.e
>> object vOldSeed vOldSeed = #69F5C10D
>>
>> function rand32(atom N)
>>     integer a, b
>>     sequence d
>>     atom X
>>
>>     d = date()
>>     d = vOldSeed * d
>>     vOldSeed = d[1] + d[2] + d[3] + d[4] + d[5] + d[6]
>>     vOldSeed += time() * (time() + 17)
>>     vOldSeed = floor(remainder(vOldSeed * (vOldSeed - 3), #3FFFFFFF))
>>     set_rand(vOldSeed)
>>     a = rand(#3FFFFFFF)
>>     vOldSeed += d[4] + d[5] + d[6]
>>     vOldSeed += (time() + 3.1427) * (time() + 619)
>>     vOldSeed = floor(remainder(vOldSeed * (vOldSeed - 3), #3FFFFFFF))
>>     set_rand(vOldSeed)
>>     b = rand(#3FFFFFFF)
>>     X =  and_bits(a, #FFFF) * #10000 + and_bits(b, #FFFF)
>>     return floor(X - floor(X/N)*N) + 1
>>
>> end function
>> constant debug = find("DEBUG:RAND32", command_line())
>> if debug then
>> for i = 1 to 32 do
>>     printf(1, "%4d ", rand32(2))
>> end for
>> end if
>
> Cool. Thanks, Derek!

I made a synthesis of yours and Tommy's code. 

function rand32 (atom n)
   -- Produces a pseudo-random integer between 1 and n
   atom x
   integer hiWord, loWord

   if n <= #3FFFFFFF then
      return rand(n)
   else
      hiWord = rand(#10000) - 1
      loWord = rand(#10000) - 1
      x = hiWord*#10000 + loWord
      return remainder(x, floor(n)) + 1
   end if
end function

Derek, do you think using set_rand() is essential here?

Regards,
   Juergen