Severi Salminen wrote:
>>   It's horribly ugly C code. I have made a clean C++ implementation if
>> you are interested.
> 
> Actually I'm interested.

http://warp.povusers.org/IsaacRand.zip

  If you want to increase the cryptographical strength of the RNG,
increase the value of RANDSIZL in the IsaacRand.hh file. According to
the author, values between 4 and 8 should be ok. The larger the value,
the (cryptographically) stronger the results (and the larger the cycle),
at the cost of the class taking more memory.
  (One instance of the class requires 4*4 + 4*2*2^RANDSIZL bytes. For
example with RANDSIZL 4 the amount of space required is 144 bytes, while
with RANDSIZL 8 it requires 2064 bytes.)

  According to the author, a value of 4 for RANDSIZL should be enough
for your purposes. You could try 5 or 6, though.

  (Curiously, as I found out recently, increasing this size actually
makes the RNG slightly faster. For instance, increasing RANDSIZL from 4
to 8 makes the RNG approximately 10% faster in my computer.)

> Do you know how it compares to Mersenne Twister speed-wise?

  Unfortunately I don't. However, I believe this RNG to be very fast,
especially taking into account the high quality of the results.

> I don't need 100% cryptographic robustness but fast
> generation and decent randomness for (say) 1280x1024x10x10000 numbers.
> (resolution * rays/pixel * passes). So the cycle must be a lot larger
> than that :)

  Increasing RANDSIZL increases the smallest cycle, but even with 4 I
think it's pretty large.

Post a reply to this message