From 702c02383cd35685133e1970a1d3d78652107c75 Mon Sep 17 00:00:00 2001
From: g1n <g1n@ttm.sh>
Date: Fri, 15 Oct 2021 14:27:10 +0300
Subject: [PATCH] Add DEX and DEY instructions

---
 src/6502/6502.h |  3 +++
 src/6502/main.c | 12 ++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/src/6502/6502.h b/src/6502/6502.h
index 8cc8c14..e1cfcae 100644
--- a/src/6502/6502.h
+++ b/src/6502/6502.h
@@ -41,6 +41,9 @@ typedef unsigned short word; // 16 bit
 #define INS_INX 0xE8 // INX Implied
 #define INS_INY 0xC8 // INY Implied
 
+#define INS_DEX 0xCA // DEX Implied
+#define INS_DEY 0x88 // DEY Implied
+
 struct MEMORY {
 	byte memory[MAX_MEMORY];
 };
diff --git a/src/6502/main.c b/src/6502/main.c
index 5a7e851..8936ac0 100644
--- a/src/6502/main.c
+++ b/src/6502/main.c
@@ -175,6 +175,7 @@ void execute() {
 				break;
 		        case INS_NOP:
 			        break;
+				
          		case INS_INX:
 			        cpu.X++;
 			        cpu.Z = (cpu.X == 0);
@@ -185,6 +186,17 @@ void execute() {
 			        cpu.Z = (cpu.Y == 0);
 				cpu.N = (cpu.Y & 0b1000000) > 0;
 			        break;
+
+		        case INS_DEX:
+			        cpu.X--;
+			        cpu.Z = (cpu.X == 0);
+				cpu.N = (cpu.X & 0b1000000) > 0;
+			        break;
+		        case INS_DEY:
+			        cpu.Y--;
+			        cpu.Z = (cpu.Y == 0);
+				cpu.N = (cpu.Y & 0b1000000) > 0;
+			        break;
 		        case 0x00: // EOF
 			        return;
 			default: