0xe8の実装

src/main.rs

@@ -25,6 +25,15 @@ impl CPU {
         self.update_zero_and_negative_flags(self.register_x);
     }
 
+    fn inx(&mut self) {
+        if self.register_x == 0xff {
+            self.register_x = 0;
+        } else {
+            self.register_x += 1;
+        }
+        self.update_zero_and_negative_flags(self.register_x);
+    }
+
     fn update_zero_and_negative_flags(&mut self, result: u8) {
         if result == 0 {
             self.status = self.status | 0b0000_0010;
@@ -46,16 +55,15 @@ impl CPU {
             self.program_counter += 1;
 
             match opcode {
-                // LDA
                 0xA9 => {
                     // Fetch a parameter
                     let param = program[self.program_counter as usize];
                     self.program_counter += 1;
 
                     self.lda(param);
                 }
-                // TAX
                 0xAA => self.tax(),
+                0xE8 => self.inx(),
                 0x00 => {
                     return;
                 }
@@ -107,4 +115,32 @@ mod test {
         assert!(cpu.status & 0b0000_0010 == 0b00);
         assert!(cpu.status & 0b1000_0000 == 0b1000_0000);
     }
+
+    #[test]
+    fn test_0xe8_inx_increment_x() {
+        let mut cpu = CPU::new();
+        cpu.register_x = 0x7F;
+        assert!(cpu.status & 0b1000_0000 != 0b1000_0000);
+        cpu.interpret(vec![0xe8, 0x00]);
+        assert_eq!(cpu.register_x, 0x80);
+        assert!(cpu.status & 0b0000_0010 == 0b00);
+        assert!(cpu.status & 0b1000_0000 == 0b1000_0000);
+    }
+
+    #[test]
+    fn test_5_ops_working_together() {
+        let mut cpu = CPU::new();
+        cpu.interpret(vec![0xa9, 0xc0, 0xaa, 0xe8, 0x00]);
+
+        assert_eq!(cpu.register_x, 0xc1)
+    }
+
+    #[test]
+    fn test_inx_overflow() {
+        let mut cpu = CPU::new();
+        cpu.register_x = 0xff;
+        cpu.interpret(vec![0xe8, 0xe8, 0x00]);
+
+        assert_eq!(cpu.register_x, 1)
+    }
 }