26 lines
838 B
Haskell
26 lines
838 B
Haskell
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#!/usr/bin/env nix-script
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#!>haskell
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{- Mathematical way to convert a diceware number. -}
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import Data.List (elemIndex)
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-- | Convert a decimal numeral n into k-adic base system.
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--
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-- \boldsymbol{A}_k(n) = \sum_{j=0}^{m-1} 10^j \ [1 + \delta_j \mod k]
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-- where m = \bigl \lfloor \log_k [n(k-1)+1] \bigr \rfloor
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-- \delta_j = \left \lfloor\frac{n(k-1)+1-k^m}{k^j(k-1)} \right \rfloor
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a :: Int -> Int -> Int
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a k n = sum [(1 + (d j) `mod` k) * 10^j | j <- [0..m-1]]
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where
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m = floor $ logBase k' (n'*(k'-1) + 1)
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d j = (n*(k-1) + 1 - k^m) `div` ((k-1) * k^j)
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(k', n') = (fromIntegral k, fromIntegral n)
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interact' :: (String -> String) -> IO ()
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interact' f = interact (unlines . map f . lines)
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main :: IO ()
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main = interact' (show . d . read) where
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d = flip elemIndex $ map (a 6 . (+1555)) [0..7775]
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