base64

commit e01f8d10d9bafcab783a6a3bce9ae1b31d6223b6
parent 72fa80fdb1438d0d10e0f536558afd2ddbd593c8
Author: Jared Tobin <jared@jtobin.io>
Date:   Sat, 16 May 2026 13:00:26 -0230

lib: dispatch encode/decode to ARM NEON when available

Wire 'Data.ByteString.Base64.encode' and 'decode' to the NEON
implementation added in the previous commit, with the pure Haskell
scalar loop kept as a fallback.

Mirrors the dispatch pattern in ppad-base16 / ppad-sha256:

    encode bs
      | Arm.base64_arm_available = Arm.encode bs
      | otherwise                = encode_scalar bs

No behavioural change beyond dispatch: on aarch64 the NEON path is
taken, on every other arch the C stubs return availability = 0 and
the scalar bodies run.

Existing tasty suite (5000 QuickCheck cases × 3 properties + the
RFC 4648 §10 unit vectors) passes through the dispatched path,
including under 'cabal test -fllvm -fsanitize' which exercises the
C kernel under AddressSanitizer + UndefinedBehaviorSanitizer.

Performance on 1 KiB inputs, M4 MacBook Air, GHC 9.10.3 + LLVM 19,
-fllvm:

  encode time:   270 ns -> 102 ns   (~2.6×)
  decode time:   273 ns -> 160 ns   (~1.7×)

Diffstat:
M
lib/Data/ByteString/Base64.hs
 | 
17
+++++++++++++----

1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/lib/Data/ByteString/Base64.hs b/lib/Data/ByteString/Base64.hs
@@ -18,6 +18,7 @@ module Data.ByteString.Base64 (
 import qualified Data.Bits as B
 import Data.Bits ((.&.), (.|.))
 import qualified Data.ByteString as BS
+import qualified Data.ByteString.Base64.Arm as Arm
 import qualified Data.ByteString.Internal as BI
 import Data.Word (Word8)
 import Foreign.ForeignPtr (withForeignPtr)
@@ -75,23 +76,31 @@ dec_tab =
 
 -- | Encode a base256 'ByteString' as base64.
 --
+--   Uses ARM NEON extensions when available, otherwise a pure
+--   Haskell scalar loop.
+--
 --   >>> encode "hello world"
 --   "aGVsbG8gd29ybGQ="
 encode :: BS.ByteString -> BS.ByteString
-encode = encode_scalar
+encode bs
+  | Arm.base64_arm_available = Arm.encode bs
+  | otherwise                = encode_scalar bs
 {-# INLINABLE encode #-}
 
 -- | Decode a base64 'ByteString' to base256.
 --
---   Invalid inputs (including incorrectly-padded or non-canonical
---   inputs) will produce 'Nothing'.
+--   Uses ARM NEON extensions when available, otherwise a pure
+--   Haskell scalar loop.  Invalid inputs (including incorrectly-
+--   padded or non-canonical inputs) will produce 'Nothing'.
 --
 --   >>> decode "aGVsbG8gd29ybGQ="
 --   Just "hello world"
 --   >>> decode "aGVsbG8gd29ybGQ" -- missing padding
 --   Nothing
 decode :: BS.ByteString -> Maybe BS.ByteString
-decode = decode_scalar
+decode bs
+  | Arm.base64_arm_available = Arm.decode bs
+  | otherwise                = decode_scalar bs
 {-# INLINABLE decode #-}
 
 encode_scalar :: BS.ByteString -> BS.ByteString