Jun-ichiro itojun Hagino wrote:

> > BTW, I also analyzed why "seed2" failed the way it did.
> > 
> > The important thing to note is that, when using a prime modulus, the modular 
> > exponentiation has a cycle of modulus-1 (i.e. RU_N-1).  That is to say, the 
> > exponent RU_N-1 generates the same output as the exponent 0, RU_N the same as 
> > 1, etc.  The xor was causing aliasing.
> > 
> > Replacing the xor with an addition fixes this problem, but I'm not sure 
> > whether it has the desired behavior in other regards.
> 
> 	just changing xor into addition will consistute problem.  the topmost
> 	bit is used for special purpose, so the addition must be performed
> 	in mod 2^15 space.

The xor (or add) is used on the exponent argument passed to the pmod
function and thus it's value doesn't affect the high bit.

Simon.
--
Simon Burge                            <simonb@wasabisystems.com>
NetBSD Support and Service:         http://www.wasabisystems.com/