From 131b0f312db3e9676aa9eb617ee1da28820653dd Mon Sep 17 00:00:00 2001
From: Sam M W <you@example.com>
Date: Sun, 2 Apr 2023 21:35:18 +0100
Subject: [PATCH] remove get_byte_mut_ref method from Memory

This is the right thing to do, because the actual hardware will perform
a read and then perform a write. This could have observable side effects
on a real system
---
 src/cpu.rs    | 42 ++++++++++++++++++------------------------
 src/memory.rs |  4 ----
 2 files changed, 18 insertions(+), 28 deletions(-)

diff --git a/src/cpu.rs b/src/cpu.rs
index ff81865..c4208bc 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -103,10 +103,9 @@ impl CPU {
                 self.registers.accumulator = val as i8;
             }
             (Instruction::ASL, OpInput::UseAddress(addr)) => {
-                CPU::shift_left_with_flags(
-                    self.memory.get_byte_mut_ref(addr),
-                    &mut self.registers.status,
-                );
+                let mut operand: u8 = self.memory.get_byte(addr);
+                CPU::shift_left_with_flags(&mut operand, &mut self.registers.status);
+                self.memory.set_byte(addr, operand);
             }
 
             (Instruction::BCC, OpInput::UseRelative(rel)) => {
@@ -208,10 +207,9 @@ impl CPU {
             }
 
             (Instruction::DEC, OpInput::UseAddress(addr)) => {
-                CPU::decrement(
-                    self.memory.get_byte_mut_ref(addr),
-                    &mut self.registers.status,
-                );
+                let mut operand: u8 = self.memory.get_byte(addr);
+                CPU::decrement(&mut operand, &mut self.registers.status);
+                self.memory.set_byte(addr, operand);
             }
 
             (Instruction::DEY, OpInput::UseImplied) => {
@@ -231,10 +229,9 @@ impl CPU {
             }
 
             (Instruction::INC, OpInput::UseAddress(addr)) => {
-                CPU::increment(
-                    self.memory.get_byte_mut_ref(addr),
-                    &mut self.registers.status,
-                );
+                let mut operand: u8 = self.memory.get_byte(addr);
+                CPU::increment(&mut operand, &mut self.registers.status);
+                self.memory.set_byte(addr, operand);
             }
             (Instruction::INX, OpInput::UseImplied) => {
                 CPU::increment(&mut self.registers.index_x, &mut self.registers.status);
@@ -282,10 +279,9 @@ impl CPU {
                 self.registers.accumulator = val as i8;
             }
             (Instruction::LSR, OpInput::UseAddress(addr)) => {
-                CPU::shift_right_with_flags(
-                    self.memory.get_byte_mut_ref(addr),
-                    &mut self.registers.status,
-                );
+                let mut operand: u8 = self.memory.get_byte(addr);
+                CPU::shift_right_with_flags(&mut operand, &mut self.registers.status);
+                self.memory.set_byte(addr, operand);
             }
 
             (Instruction::ORA, OpInput::UseImmediate(val)) => {
@@ -327,10 +323,9 @@ impl CPU {
                 self.registers.accumulator = val as i8;
             }
             (Instruction::ROL, OpInput::UseAddress(addr)) => {
-                CPU::rotate_left_with_flags(
-                    self.memory.get_byte_mut_ref(addr),
-                    &mut self.registers.status,
-                );
+                let mut operand: u8 = self.memory.get_byte(addr);
+                CPU::rotate_left_with_flags(&mut operand, &mut self.registers.status);
+                self.memory.set_byte(addr, operand);
             }
             (Instruction::ROR, OpInput::UseImplied) => {
                 // Accumulator mode
@@ -339,10 +334,9 @@ impl CPU {
                 self.registers.accumulator = val as i8;
             }
             (Instruction::ROR, OpInput::UseAddress(addr)) => {
-                CPU::rotate_right_with_flags(
-                    self.memory.get_byte_mut_ref(addr),
-                    &mut self.registers.status,
-                );
+                let mut operand: u8 = self.memory.get_byte(addr);
+                CPU::rotate_right_with_flags(&mut operand, &mut self.registers.status);
+                self.memory.set_byte(addr, operand);
             }
 
             (Instruction::SBC, OpInput::UseImmediate(val)) => {
diff --git a/src/memory.rs b/src/memory.rs
index 1929365..097c110 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -69,10 +69,6 @@ impl Memory {
         self.bytes[address as usize]
     }
 
-    pub fn get_byte_mut_ref(&mut self, address: u16) -> &mut u8 {
-        &mut self.bytes[address as usize]
-    }
-
     pub fn get_slice(&self, start: u16, diff: u16) -> &[u8] {
         let orig: usize = start.into();
         let end = orig + diff as usize;