secp256k1

commit 87fb7fe848f01d90e98508aed1fcec27fc29cb94
parent 07e360a0da43053bff65c81f5e992fb37fa4e996
Author: Jared Tobin <jared@jtobin.io>
Date:   Tue, 23 Dec 2025 07:30:45 -0330

lib: dumber/faster modQ

Diffstat:
M
lib/Crypto/Curve/Secp256k1.hs
 | 
7
+++++--

1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/lib/Crypto/Curve/Secp256k1.hs b/lib/Crypto/Curve/Secp256k1.hs
@@ -283,9 +283,12 @@ unroll32 (Wider (# w0, w1, w2, w3 #)) =
     Storable.pokeByteOff ptr 31 (word8 w0)
 {-# INLINABLE unroll32 #-}
 
--- cheeky montgomery-assisted modQ
+-- modQ via conditional subtraction
 modQ :: Wider -> Wider
-modQ = S.from . S.to
+modQ x =
+  let !(Wider xw) = x
+      !(Wider qw) = _CURVE_Q
+  in  W.select x (x - _CURVE_Q) (CT.not# (W.lt# xw qw))
 {-# INLINABLE modQ #-}
 
 -- bytewise xor