[Internal] add a utility to dump byte array in hexadecimal

Crypto/Internal/Hex.hs

@@ -0,0 +1,57 @@
+-- |
+-- Module      : Crypto.Internal.Hex
+-- License     : BSD-style
+-- Maintainer  : Vincent Hanquez <vincent@snarc.org>
+-- Stability   : experimental
+-- Portability : unknown
+--
+-- Hexadecimal escaper
+--
+{-# LANGUAGE MagicHash #-}
+{-# LANGUAGE UnboxedTuples #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE BangPatterns #-}
+module Crypto.Internal.Hex
+    ( showHexadecimal
+    ) where
+
+import Crypto.Internal.Compat
+import Data.Word
+import GHC.Prim
+import GHC.Types
+import Foreign.Storable
+import Foreign.Ptr (Ptr)
+
+showHexadecimal :: Ptr Word8 -> Int -> String
+showHexadecimal ptr len = loop 0
+  where
+        loop i
+            | i == len  = []
+            | otherwise =
+                let b = fromIntegral (byteIndex i)
+                 in toEnum (r tableHi b) : toEnum (r tableLo b) : loop (i+1)
+
+        byteIndex :: Int -> Word8
+        byteIndex i = unsafeDoIO (peekByteOff ptr i)
+
+        r :: Addr# -> Int -> Int
+        r table (I# index) = I# (word2Int# (indexWord8OffAddr# table index))
+
+        !tableLo =
+            "0123456789abcdef0123456789abcdef\
+            \0123456789abcdef0123456789abcdef\
+            \0123456789abcdef0123456789abcdef\
+            \0123456789abcdef0123456789abcdef\
+            \0123456789abcdef0123456789abcdef\
+            \0123456789abcdef0123456789abcdef\
+            \0123456789abcdef0123456789abcdef\
+            \0123456789abcdef0123456789abcdef"#
+        !tableHi =
+            "00000000000000001111111111111111\
+            \22222222222222223333333333333333\
+            \44444444444444445555555555555555\
+            \66666666666666667777777777777777\
+            \88888888888888889999999999999999\
+            \aaaaaaaaaaaaaaaabbbbbbbbbbbbbbbb\
+            \ccccccccccccccccdddddddddddddddd\
+            \eeeeeeeeeeeeeeeeffffffffffffffff"#