fixed

commit 87c28f17c8d5ca7e73f44b4f47de2f10c92d6562
parent 73eca8c98fb444609b725a557eb4406b943132de
Author: Jared Tobin <jared@jtobin.io>
Date:   Sun, 30 Nov 2025 12:57:18 +0400

limb: input mask on sub, return mask

Diffstat:
M
lib/Data/Word/Limb.hs
 | 
6
++++--

1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/lib/Data/Word/Limb.hs b/lib/Data/Word/Limb.hs
@@ -300,8 +300,10 @@ sub_b#
   -> Limb              -- ^ subtrahend
   -> Limb              -- ^ borrow
   -> (# Limb, Limb #)  -- ^ (# difference, new borrow #)
-sub_b# (Limb m) (Limb n) (Limb b) =
-  let !(# d0, b0 #) = Exts.subWordC# m n
+sub_b# (Limb m) (Limb n) (Limb a) =
+  let !s = case B.finiteBitSize (0 :: Word) of Exts.I# bs -> bs Exts.-# 1#
+      !b = Exts.uncheckedShiftRL# a s
+      !(# d0, b0 #) = Exts.subWordC# m n
       !(#  d, b1 #) = Exts.subWordC# d0 b
       !c = Exts.int2Word# (Exts.negateInt# (Exts.orI# b0 b1))
   in  (# Limb d, Limb c #)