Question

我在Haskell中实施了Miller Rabin测试。我试图严格遵循例如在Miller Rabin测试的维基百科条目中给出的伪代码。现在我在网上发现，对于某些证人的选择，测试是确定性的，直到某些给定的界限。我对2 ^ 64下的素数很感兴趣，所以我在这篇文章中找到了足够的界限 What witnesses do i need for Rabin-Miller test for numbers up to 10¹⁸?。但是，代码似乎适用于我测试过的大多数小素数，但对于一些较大的素数则无效。例如，我尝试了十位数的素数5915587277，测试返回false。我认为我的实施是正确的，但希望有人可以发现我犯了错误并且误解了MR测试。在此先感谢您的帮助。此外，抱歉看起来很乱。

isPrime :: Int -> Bool
isPrime n = millerRabinTest n (factorizeN (n-1))

{- factorizeN finds a number s and odd number d such that n -1 = (2^s)d by 
succesively dividing n by two if it is even. -}
factorizeN :: Int -> (Int, Int)
factorizeN n = fN n 0
  where
    fN n s | even n    = fN (n `div` 2) (s + 1)
           | otherwise = (n,s)

{- this is the main function. it takes w values from a set of witnesses
and checks if n passes the test. If it doesn't, n is not prime, if it does 
for all w, it is probably prime. -}
millerRabinTest :: Int -> (Int,Int) -> Bool
millerRabinTest n (d,s) = and [test n (expmod w d n) s | w <- onesToCheck]

{- this is the test that is used in the millerRabinTest function. it sees if
w^d = 1 mod n  or n-1 mod n, if not it multiplies by two
and checks again for a total of s-1 times. If it is never true then the number 
is not prime -}
test :: Int -> Int -> Int -> Bool
test n w s | w `elem` [1,n-1] = True
           | otherwise        = or [ (expmod w (2^k) n) `elem` [1,n-1]| k <- [1..s]]   

{- set of witnesses that should make the Miller Rabin test deterministic if
n < 2^64. -}
onesToCheck :: [Int]
onesToCheck = [2,325,9375,28178,450775,9780504,1795265022]

{- function that calculates a^e mod n. -}
expmod :: Int -> Int -> Int -> Int
expmod a e n  | e == 1           = a `mod` n
              | (e `mod` 2) == 0 = (expmod ((a*a) `mod` n) (e `div` 2) n)
              | otherwise        = (a*(expmod ((a*a) `mod` n) (e `div` 2) n)) `mod` n

Answer 1

当您计算Int时，expmod可能会在a*a中溢出Int。 Int是一个机器大小的整数，不超过64位。您应该使用Integer（任意精度整数类型）替换程序中{{1}}的某些实例。

为什么我的Miller Rabin算法不起作用（Haskell）？

1 个答案: