H6502/my.patch at main · damiik/H6502 · GitHub

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--- a/src/MOS6502Emulator/Instructions.hs
+++ b/src/MOS6502Emulator/Instructions.hs
@@ -393,59 +393,55 @@
-modifyOperand :: AddressMode -> (Word8 -> FDX Word8) -> FDX ()
-modifyOperand Immediate _ = return () -- TODO: should this be an error?
-modifyOperand Zeropage op = do
-  b  <- fetchByteAtPC
-  b' <- op b
-  writeByteMem (toWord b) b'
-modifyOperand ZeropageX op = do
-  b <- fetchByteAtPC
-  x <- getReg rX
-  let addr = toWord (b + x) -- stay on the zeropage but add x
-  v <- fetchByteMem addr
-  v' <- op v
-  writeByteMem addr v'
-modifyOperand ZeropageY op = do
-  b <- fetchByteAtPC
-  y <- getReg rY
-  let addr = toWord (b + y) -- stay on the zeropage but add y
-  v <- fetchByteMem addr
-  v' <- op v
-  writeByteMem addr v'
-modifyOperand Absolute  op = do
-  addr <- fetchWordAtPC
-  b  <- fetchByteMem addr
-  b' <- op b
-  writeByteMem addr b'
-modifyOperand AbsoluteX op = do
-  w <- fetchWordAtPC
-  x <- getReg rX
-  -- TODO: what does it mean to increment the address with carry?
-  -- I think it means that you convert x to 16 bit and then add
-  let addr = w + toWord x
-  b  <- fetchByteMem addr
-  b' <- op b
-  writeByteMem addr b'
-modifyOperand AbsoluteY op = do
-  w <- fetchWordAtPC
-  y <- getReg rY
-  -- TODO: what does it mean to increment the address with carry?
-  -- I think it means that you convert y to 16 bit and then add
-  let addr = w + toWord y
-  b  <- fetchByteMem addr
-  b' <- op b
-  writeByteMem addr b' -- Corrected typo here (was v')
-modifyOperand IndirectX op = do
-  b <- fetchByteAtPC
-  x <- getReg rX
-  let zeroPageAddr = b + x -- zeropage indexed by b + x
-  addr <- fetchWordMem zeroPageAddr
-  v    <- fetchByteMem addr
-  v'   <- op v
-  writeByteMem addr v'
-modifyOperand IndirectY op = do
-  b <- fetchByteAtPC
-  y <- getReg rY
-  v1 <- fetchWordMem b -- zeropage indexed by b, add y to result
-  let addr = v1 + toWord y
-  v  <- fetchByteMem addr
-  v' <- op v
-  writeByteMem addr v'
+modifyOperand :: AddressMode -> (Word8 -> FDX Word8) -> FDX ()
+modifyOperand Immediate _ = return () -- Cannot write to immediate
+modifyOperand Zeropage op = do
+  zpAddr <- fetchAndIncPC
+  v <- fetchByteMem (toWord zpAddr)
+  v' <- op v
+  writeByteMem (toWord zpAddr) v'
+modifyOperand ZeropageX op = do
+  zpAddr <- fetchAndIncPC
+  x <- getReg rX
+  let addr = toWord (zpAddr + x)
+  v <- fetchByteMem addr
+  v' <- op v
+  writeByteMem addr v'
+modifyOperand ZeropageY op = do
+  zpAddr <- fetchAndIncPC
+  y <- getReg rY
+  let addr = toWord (zpAddr + y)
+  v <- fetchByteMem addr
+  v' <- op v
+  writeByteMem addr v'
+modifyOperand Absolute op = do
+  addr <- fetchWordAndIncPC
+  v <- fetchByteMem addr
+  v' <- op v
+  writeByteMem addr v'
+modifyOperand AbsoluteX op = do
+  base <- fetchWordAndIncPC
+  x <- getReg rX
+  let addr = base + toWord x
+  v <- fetchByteMem addr
+  v' <- op v
+  writeByteMem addr v'
+modifyOperand AbsoluteY op = do
+  base <- fetchWordAndIncPC
+  y <- getReg rY
+  let addr = base + toWord y
+  v <- fetchByteMem addr
+  v' <- op v
+  writeByteMem addr v'
+modifyOperand IndirectX op = do
+  zpAddr <- fetchAndIncPC
+  x <- getReg rX
+  addr <- fetchWordMem (zpAddr + x)
+  v <- fetchByteMem addr
+  v' <- op v
+  writeByteMem addr v'
+modifyOperand IndirectY op = do
+  zpAddr <- fetchAndIncPC
+  y <- getReg rY
+  base <- fetchWordMem zpAddr
+  let addr = base + toWord y
+  v <- fetchByteMem addr
+  v' <- op v
+  writeByteMem addr v'
@@