From 45339997c863a7798839de76265b4c1182345711 Mon Sep 17 00:00:00 2001
From: pingu <nor@acorneroftheweb.com>
Date: Mon, 30 Mar 2026 13:59:53 +0200
Subject: [PATCH] All the 8bit arithmetic things done

---
 src/GB/CPU.hs | 44 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 36 insertions(+), 8 deletions(-)

diff --git a/src/GB/CPU.hs b/src/GB/CPU.hs
index bb563ba..1205a8c 100644
--- a/src/GB/CPU.hs
+++ b/src/GB/CPU.hs
@@ -9,13 +9,12 @@ import Lens.Micro.Platform
 import Data.Word
 import Data.Bits
 import qualified Data.Vector.Sized as V
-import Prelude hiding (subtract)
 
 class Convert a b where
   convert :: a -> b
 
 data FlagRegister = FlagRegister { _zero      :: Bool
-                                 , _subtract  :: Bool
+                                 , _negative  :: Bool
                                  , _halfCarry :: Bool
                                  , _carry     :: Bool
                                  }
@@ -25,8 +24,8 @@ makeLenses ''FlagRegister
 
 zeroFlagPosition :: Int
 zeroFlagPosition = 7
-subtractFlagPosition :: Int
-subtractFlagPosition = 6
+negativeFlagPosition :: Int
+negativeFlagPosition = 6
 halfCarryFlagPosition :: Int
 halfCarryFlagPosition = 5
 carryFlagPosition :: Int
@@ -35,14 +34,14 @@ carryFlagPosition = 4
 instance Convert FlagRegister Word8 where
   convert r =
     ((`shiftL` zeroFlagPosition) $ if r ^. zero then 1 else 0) +
-    ((`shiftL` subtractFlagPosition) $ if r ^. subtract then 1 else 0) +
+    ((`shiftL` negativeFlagPosition) $ if r ^. negative then 1 else 0) +
     ((`shiftL` halfCarryFlagPosition) $ if r ^. halfCarry then 1 else 0) +
     ((`shiftL` carryFlagPosition) $ if r ^. carry then 1 else 0)
   
 instance Convert Word8 FlagRegister where
   convert w =
     let _zero = (shiftR w zeroFlagPosition .&. 1 /= 0)
-        _subtract = (shiftR w subtractFlagPosition .&. 1 /= 0)
+        _negative = (shiftR w negativeFlagPosition .&. 1 /= 0)
         _halfCarry = (shiftR w halfCarryFlagPosition .&. 1 /= 0)
         _carry = (shiftR w carryFlagPosition .&. 1 /= 0) in
       FlagRegister {..}
@@ -96,6 +95,13 @@ data Instruction where
   IncHL :: Instruction
   DecR :: ArithmeticTarget -> Instruction
   DecHL :: Instruction
+  BOR :: ArithmeticTarget -> (Word8 -> Word8 -> Word8) -> FlagRegister -> Instruction
+  BOHL :: (Word8 -> Word8 -> Word8) -> FlagRegister -> Instruction
+  BON :: Word8 -> (Word8 -> Word8 -> Word8) -> FlagRegister -> Instruction
+  CCF :: Instruction
+  SCF :: Instruction
+  DAA :: Instruction -- TODO: What does this do?
+  CPL :: Instruction
 
 execute :: CPU -> Instruction -> CPU
 execute cpu = \case
@@ -135,11 +141,33 @@ execute cpu = \case
                value = fetch cpu target
                (newValue, newFlags) = sub value 1 False in
            write cpu target newValue & registers . flags .~ newFlags
+  BOR t op _f -> let newValue = (cpu ^. registers . a) `op` (cpu ^. registers . t)
+                     newFlags = _f {_zero = newValue == 0} in
+                cpu & registers . a .~ newValue & registers . flags .~ newFlags
+  BOHL op _f -> let target = getHL $ cpu ^. registers
+                    value = fetch cpu target
+                    newValue = (cpu ^. registers . a) `op` value
+                    newFlags = _f {_zero = value == 0} in
+                cpu & registers . a .~ newValue & registers . flags .~ newFlags
+            
+  BON value op _f -> let newValue = (cpu ^. registers . a) `op` value
+                         newFlags = _f {_zero = newValue == 0} in
+                    cpu & registers . a .~ newValue & registers . flags .~ newFlags
+  CCF -> cpu & registers . flags . negative .~ False
+             & registers . flags . halfCarry .~  False
+             & registers . flags . carry %~ not
+  SCF -> cpu & registers . flags . negative .~ False
+             & registers . flags . halfCarry .~  False
+             & registers . flags . carry .~ True
+  DAA -> undefined -- TODO: undefined in manual
+  CPL -> cpu & registers . a %~ complement
+             & registers . flags . negative .~ True
+             & registers . flags . halfCarry .~ True
   where
     add :: Word8 -> Word8 -> Bool -> (Word8, FlagRegister)
     add o n _c = let new        = o + n + if _c then 1 else 0
                      _zero      = new == 0
-                     _subtract  = False
+                     _negative  = False
                      _carry     = o > new
                      _halfCarry = o .&. 16 + n .&. 16 > 16 in
                  (new, FlagRegister {..})
@@ -147,7 +175,7 @@ execute cpu = \case
     sub :: Word8 -> Word8 -> Bool -> (Word8, FlagRegister)
     sub o n _c = let new        = o - n - if _c then 1 else 0
                      _zero      = new == 0
-                     _subtract  = True
+                     _negative  = True
                      _carry     = o > new
                      _halfCarry = o .&. 16 + n .&. 16 > 16 in
                  (new, FlagRegister {..})