51 lines
1.7 KiB
Haskell
51 lines
1.7 KiB
Haskell
import Text.Read (readMaybe)
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import System.Exit (exitSuccess)
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import Data.Bits
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import Utils (askNumber)
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main :: IO ()
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main = do
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n <- askNumber "Enter an integer n>1 to factor:"
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b <- askNumber "Enter the bound B:"
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putStrLn ("n = " ++ show n)
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case pollardP1 n b of
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Just factor -> do
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putStrLn ("Found factor: " ++ show factor)
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let otherFactor = n `div` factor
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putStrLn ("Other factor: " ++ show otherFactor)
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Nothing -> do
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putStrLn "Failed to find a factor using Pollard p-1 method. n could be prime or different parameters needed."
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-- Pollard p-1 factorization algorithm
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pollardP1 :: Integer -> Integer -> Maybe Integer
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pollardP1 n b = tryBases [2..5]
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where
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tryBases [] = Nothing
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tryBases (a:as) =
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case pollardP1WithParams n a b of
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Just factor -> Just factor
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Nothing -> tryBases as
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-- Pollard p-1 with configurable parameters
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pollardP1WithParams :: Integer -> Integer -> Integer -> Maybe Integer
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pollardP1WithParams n a b = go a 2
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where
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go currentA k
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| k > b = Nothing -- Bound exceeded, failed to find factor
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| otherwise =
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let newA = modExp currentA k n
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d = gcd (newA - 1) n
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in if d > 1 && d < n
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then Just d -- Found a non-trivial factor
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else if d == n
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then Nothing -- Found n itself, try with different parameters
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else go newA (k + 1)
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-- Modular exponentiation: compute a^b mod m
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modExp :: Integer -> Integer -> Integer -> Integer
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modExp b 0 m = 1
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modExp b e m = t * modExp ((b * b) `mod` m) (shiftR e 1) m `mod` m
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where t = if testBit e 0 then b `mod` m else 1
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