From: SinaPtayAsiaM AT hotmail DOT com (Philip Snowberger)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: how about "more" random ? SPEED???
Date: Sun, 22 Aug 1999 17:20:40 GMT
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References: <199907311044 DOT GAA17866 AT delorie DOT com> <37A3D14C DOT A90398BE AT cartsys DOT com>
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To: djgpp AT delorie DOT com
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>> I was wondering about how fast rand actually executes, Is it something to
>> consider when using it alot or is it virtually unnoticable? Is there anyway
>> to avoid the multiplications and mods?  Is there a better alternative like
>> making some kind of randomness look-up-table or something?

well, you could create a rather large array of longs containing a
series of random values, and then have a function that returns the
next one in the list and increments the index from which the next one
should be grabbed... something like the following:

//begin untested junk

class RandomList {
private:
   long list[64*1024];
   long index;
public:
   RandomList();
   ~RandomList();
   long getNext();
}

RandomList::RandomList() {
// initialize the random number generator
// fill the list
   for (index = 0; index < 64*1024; index++)
      list[index] = rand(); // optionally do scaling & shifting here

   index = 0;
}

RandomList::~RandomList() {
}

long RandomList::getNext(void) {
   return(list[index++];
}

//end untested junk

i believe this is somewhat how POVRay does it, but don't hold me to
that, i've never looked into the code...

just my 20 yen,
--Philip Snowberger