From 19d02d1eed0886220e64f4ed87bc8da8666f8760 Mon Sep 17 00:00:00 2001
From: alekseiplusplus <alekseijeaves@protonmail.com>
Date: Mon, 27 Mar 2023 12:56:11 +1100
Subject: Added instructions, changed C and V set flag funcs

---
 applesystem.h | 24 +++++++++++++++++-------
 instruction.h | 33 ++++++++++++++++++++++++++++++---
 2 files changed, 47 insertions(+), 10 deletions(-)

diff --git a/applesystem.h b/applesystem.h
index a3a33f5..ea9b322 100644
--- a/applesystem.h
+++ b/applesystem.h
@@ -2,6 +2,12 @@ typedef unsigned char byte;
 byte acc, X, Y, S, P = 0x00;
 byte Memory[4096]; // TO DO. Add expansion capability to memory.
 
+/*
+To Do.
+	+ Find variables better passed as pointers instead
+*/
+
+
 //	FLAGS
 const byte flag_N = 0x80;	// Negative (Note that byte cast is necessary here only)
 const byte flag_V = 0x40;	// Overflow
@@ -65,8 +71,9 @@ Zero Page     ADC $44       $65  2   3
 instruction(0x65); -> ADC({enum for Zero Page}); 
 */
 // Set particular flags
-void setFlagN(){
-	if (acc ^ 0x80){
+// Functions which quickly set specific flags that are straightforward checks, and are repeated often.
+void setFlagN(byte x){
+	if (x ^ flag_N == flag_N){
 		setFlag(flag_N, 1);
 	}else{ //not sure if this should be present, I think it is
 		setFlag(flag_N, 0);
@@ -74,11 +81,13 @@ void setFlagN(){
 }
 
 //Perform prior to any changes
-void setFlagV(byte x, byte y){ //This is pathetic.
+void setFlagV(byte x, byte y){
 	if ((x & flag_N) == (y & flag_N)){
-		if (((x + y) & (flag_N ^ 0xFF)) > 0x8F) setFlag(flag_V, 1);
+		if (((x + y) & (flag_N ^ 0xFF)) > 0x7F) setFlag(flag_V, 1);
+		else setFlag(flag_V, 0);
 	}else{
-		if (((x - y) & (flag_N ^ 0xFF)) > 0x8F) setFlag(flag_V, 1);
+		if (((x - y) & (flag_N ^ 0xFF)) > 0x7F) setFlag(flag_V, 1);
+		else setFlag(flag_V, 0);
 	}
 }
 /*void setFlagB(){ //WORK ON
@@ -95,9 +104,10 @@ void setFlagZ(int x){
 		setFlag(flag_Z, 1);
 	}
 }
-void setFlagC(){ // NOTE. Must make setFlagC functional with independence. Look into carrying on 6502
+//Only 6 instructions, 2 not including stack instructions, use the carry flag.
+/*void setFlagC(){ // NOTE. Must make setFlagC functional with independence. Look into carrying on 6502
 	setFlag(flag_Z, 1);
-}
+}*/
 
 
 
diff --git a/instruction.h b/instruction.h
index af48ba0..054e629 100644
--- a/instruction.h
+++ b/instruction.h
@@ -27,9 +27,36 @@ void fSTY(Addressing addr, int val){
 	Memory[(fAddressing(addr, val))] = Y;
 }
 
+// Arithmetic Instructions
 
+void fADC(Addressing addr, int val){
+	int buffer = acc + fAddressing(addr, val);
+	setFlagV(buffer, acc);
 
-// Arithmetic Instructions
+	if (buffer > 255){
+		setFlag(flag_C, 1);
+	}else{
+		setFlag(flag_C, 0);
+	}
+
+	acc += fAddressing(addr, val);
+	setFlagN(acc);
+	setFlagZ(acc);
+}
+
+void fSBC(Addressing addr, int val){
+	int buffer = acc - fAddressing(addr, val);
+	setFlagV(buffer, acc);
+
+	if (buffer < 0){
+		setFlag(flag_C, 1);
+	}else{
+		setFlag(flag_C, 0);
+	}
+	acc -= fAddressing(addr, val);
+	setFlagN(acc);
+	setFlagZ(acc);
+}
 
 //Increment and Decrement Instructions
 
@@ -52,7 +79,7 @@ void fORA(Addressing addr, int val){
 
 void fEOR(Addressing addr, int val){
 	acc = acc ^ fAddressing(addr, val);
-	setFlagN();
+	setFlagN(acc);
 	setFlagZ(acc);
 }
 
@@ -67,7 +94,7 @@ void fEOR(Addressing addr, int val){
 void fASL(Addressing addr, int val){
 	setFlag(flag_C, (val & 0x80));
 	acc = (val << 1);
-	setFlagN();
+	setFlagN(acc);
 	setFlagZ(acc);
 }
 
-- 
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