On Thu, Sep 20, 2012 at 9:22 PM, Martin Kealey <mar...@kurahaupo.gen.nz> wrote: > On Thu, 20 Sep 2012, Stephen Pollei wrote:

> According to Wolfram, it's 75/25; so a positive result after 10 iterations > leaves about a one-in-a-million chance of being composite (more precisely, > one in 1048576). I'd believe wolfram over me, it's been a while since I've read Applied Cryptography by Schneier . >> multi method is-prime ( Int $x: Int $tries = 100) is export >> should also at least document that tries is never a negative number, >> or if it is that it has same behaviour as zero. > > Logically if "tries" is zero, is-prime shouldn't do any testing at all, and > should always return "true". (There's a chance it might be prime!) A good built in test before you try Miller-Rabin is at least test against some of the small prime numbers 2,3,5,7,11,13 otherwise even if if tries is zero saying 42 is prime is too wrong . However if only a miller-rabin style tests are used then a value of tries being zero should always return true. > If "tries" is negative, which idiom should we follow: multi method is-prime ( Int $x: UInt $tries = 100) is export I think I read somewhere that perl6 has both Int and UInt , just change the prototype multi method is-prime ( Int $x: UInt $tries = 100 where { $^n > 0 } ) is export I think I even read you can constrain it so if zero tries is completely useless you can outlaw it so document at least or change prototype to account for negative and zero values.