Cabal-syntax/src/Distribution/Utils/Base62.hs

   1 -- | Implementation of base-62 encoding, which we use when computing hashes
   2 -- for fully instantiated unit ids.
   3 module Distribution.Utils.Base62 (hashToBase62) where
   4
   5 import Data.Char (chr)
   6 import GHC.Fingerprint (Fingerprint (..), fingerprintString)
   7 import Numeric (showIntAtBase)
   8
   9 -- | Hash a string using GHC's fingerprinting algorithm (a 128-bit
  10 -- MD5 hash) and then encode the resulting hash in base 62.
  11 hashToBase62 :: String -> String
  12 hashToBase62 s = showFingerprint $ fingerprintString s
  13   where
  14     showIntAtBase62 x = showIntAtBase 62 representBase62 x ""
  15     representBase62 x
  16       | x < 10 = chr (48 + x)
  17       | x < 36 = chr (65 + x - 10)
  18       | x < 62 = chr (97 + x - 36)
  19       | otherwise = '@'
  20     showFingerprint (Fingerprint a b) = showIntAtBase62 a ++ showIntAtBase62 b