base16

commit 8e191be7f9227b4a59051b04c3e964f3f32f1155
parent 4439e0efafbb5185bd7d9bfb352a17c2a31b96b4
Author: Jared Tobin <jared@jtobin.io>
Date:   Fri, 28 Feb 2025 09:05:23 +0400

lib: more efficient word8 -> word4

Diffstat:
M
lib/Data/ByteString/Base16.hs
 | 
6
+++++-

1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/lib/Data/ByteString/Base16.hs b/lib/Data/ByteString/Base16.hs
@@ -122,8 +122,12 @@ encode bs@(BI.PS _ _ l)
         let !w16 = expand_w8 h
         in  BSB.word16BE w16 <> go16 t
 
+-- word8 hex character to word4
 word4 :: Word8 -> Maybe Word8
-word4 w8 = fmap fi (BS.elemIndex w8 hex_charset)
+word4 c
+  | c > 47 && c < 58  = pure $! c - 48
+  | c > 96 && c < 103 = pure $! c - 87
+  | otherwise         = Nothing
 {-# INLINE word4 #-}
 
 -- | Decode a base16 'ByteString' to base256.