From 5be0da1a90232d81344d702217ec961e6911f801 Mon Sep 17 00:00:00 2001
From: Lea <me@janderedev.xyz>
Date: Wed, 25 Jan 2023 19:08:00 +0100
Subject: [PATCH] turns out 8 bit processors process 8 bit numbers

---
 src/emulator/instructions/arithmetic.rs | 12 ++++++------
 src/emulator/main.rs                    | 22 +++++++++++-----------
 2 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/src/emulator/instructions/arithmetic.rs b/src/emulator/instructions/arithmetic.rs
index 2baf4dd..6af8f5d 100644
--- a/src/emulator/instructions/arithmetic.rs
+++ b/src/emulator/instructions/arithmetic.rs
@@ -12,7 +12,7 @@ fn set_cc(state: &mut EmulatorState, result: u16, flags: u8) {
 
 /// Add values of `register` and `A`
 pub fn add(register: Register, state: &mut EmulatorState) {
-    let result = get_register(register, state) + state.a as u16;
+    let result = get_register(register, state) as u16 + state.a as u16;
     set_cc(state, result, 0b1111);
     state.a = (result & 0xff) as u8;
 }
@@ -26,7 +26,7 @@ pub fn adi(byte: u8, state: &mut EmulatorState) {
 
 /// Add values of `register` and `A` and add +1 if carry bit is set
 pub fn adc(register: Register, state: &mut EmulatorState) {
-    let result = get_register(register, state) + state.a as u16 + if state.cc.c { 1 } else { 0 };
+    let result = get_register(register, state) as u16 + state.a as u16 + if state.cc.c { 1 } else { 0 };
     set_cc(state, result, 0b1111);
     state.a = (result & 0xff) as u8;
 }
@@ -41,14 +41,14 @@ pub fn aci(byte: u8, state: &mut EmulatorState) {
 /// Double precision add - Add B&C, D&E or H&L to H&L
 pub fn dad(register: Register, state: &mut EmulatorState) {
     let num = match register {
-        Register::B  => (state.b as u16) << 8 | state.c as u16,
-        Register::D  => (state.d as u16) << 8 | state.e as u16,
-        Register::H  => get_register(Register::M, state),
+        Register::B  => u16::from_le_bytes([state.c, state.b]),
+        Register::D  => u16::from_le_bytes([state.e, state.d]),
+        Register::H  => u16::from_le_bytes([state.l, state.h]),
         Register::SP => state.sp,
         _ => panic!("Cannot perform DAD on register {:?}", register),
     };
 
-    let result = num as u32 + get_register(Register::M, state) as u32;
+    let result = num as u32 + u16::from_le_bytes([state.l, state.h]) as u32;
     state.cc.c = result > 0xffff;
     state.h = (result >> 8) as u8;
     state.l = result as u8;
diff --git a/src/emulator/main.rs b/src/emulator/main.rs
index e3b3e43..f123e6c 100644
--- a/src/emulator/main.rs
+++ b/src/emulator/main.rs
@@ -58,17 +58,17 @@ fn register_from_num(b: u8) -> Register {
     }
 }
 
-fn get_register(register: Register, state: &EmulatorState) -> u16 {
+fn get_register(register: Register, state: &EmulatorState) -> u8 {
     match register {
-        Register::B => state.b as u16,
-        Register::C => state.c as u16,
-        Register::D => state.d as u16,
-        Register::E => state.e as u16,
-        Register::H => state.h as u16,
-        Register::L => state.l as u16,
-        Register::A => state.a as u16,
-        Register::M => (state.memory[(state.h as usize)] as u16) << 8 | (state.memory[state.l as usize] as u16),
-        Register::SP => state.sp,
+        Register::B => state.b as u8,
+        Register::C => state.c as u8,
+        Register::D => state.d as u8,
+        Register::E => state.e as u8,
+        Register::H => state.h as u8,
+        Register::L => state.l as u8,
+        Register::A => state.a as u8,
+        Register::M => state.memory[u16::from_le_bytes([state.l, state.h]) as usize],
+        Register::SP => unreachable!(),
     }
 }
 
@@ -81,7 +81,7 @@ fn set_register(register: Register, value: u8, state: &mut EmulatorState) {
         Register::H => state.h = value,
         Register::L => state.l = value,
         Register::A => state.a = value,
-        Register::M => panic!("Cannot set pseudoregister 'M'"),
+        Register::M => state.memory[u16::from_le_bytes([state.l, state.h]) as usize] = value,
         Register::SP => panic!("Cannot set 'SP' through set_register()"),
     };
 }