bech32

commit dbd32a5726d25cdf168f210a66a0bf602980b683
parent e9343601b5ba22d3902953df39026fb8b4d1f8e1
Author: Jared Tobin <jared@jtobin.io>
Date:   Sat, 10 Oct 2026 15:52:45 +0400

lib: select bech32 polymod generators by bit test

LLVM lowers the unrolled bit-test selection to conditional selects,
which run considerably faster than the equivalent mask arithmetic
(roughly 240ns vs 540ns over 71 words on an M4).

Diffstat:
M
lib/Data/ByteString/Bech32/Internal.hs
 | 
4
+++-

1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/lib/Data/ByteString/Bech32/Internal.hs b/lib/Data/ByteString/Bech32/Internal.hs
@@ -89,7 +89,9 @@ polymod = BS.foldl' alg 1 where
 
   -- the generator 'g' if bit 'i' of 'b' is set, else zero
   gen :: Word32 -> Int -> Word32 -> Word32
-  gen b i g = negate ((b `B.shiftR` i) .&. 1) .&. g
+  gen b i g
+    | B.testBit b i = g
+    | otherwise     = 0
   {-# INLINE gen #-}
 
 valid_hrp :: BS.ByteString -> Bool