Implement BVC instruction

README.md

@@ -28,7 +28,7 @@ A (soon to be) fully-featured NES emulator written in Rust.
 - [X] BNE
 - [X] BPL
 - [ ] BRK
-- [ ] BVC
+- [X] BVC
 - [ ] BVS
 - [ ] CLC
 - [ ] CLD

src/cpu/instructions.rs

@@ -67,9 +67,10 @@ pub static INSTRUCTIONS: Lazy<HashMap<u8, Instruction>> = Lazy::new(|| {
         Instruction {opcode: 0xB0, name: "BCS", bytes: 2, addressing_mode: AddressingMode::Relative},
         Instruction {opcode: 0xF0, name: "BEQ", bytes: 2, addressing_mode: AddressingMode::Relative},
         Instruction {opcode: 0x30, name: "BMI", bytes: 2, addressing_mode: AddressingMode::Relative},
-        Instruction {opcode: 0x10, name: "BPL", bytes: 2, addressing_mode: AddressingMode::Relative},
         Instruction {opcode: 0xD0, name: "BNE", bytes: 2, addressing_mode: AddressingMode::Relative},
+        Instruction {opcode: 0x10, name: "BPL", bytes: 2, addressing_mode: AddressingMode::Relative},
         Instruction {opcode: 0x00, name: "BRK", bytes: 1, addressing_mode: AddressingMode::Implicit},
+        Instruction {opcode: 0x50, name: "BVC", bytes: 2, addressing_mode: AddressingMode::Relative},
         Instruction {opcode: 0xA9, name: "LDA", bytes: 2, addressing_mode: AddressingMode::Immediate},
         Instruction {opcode: 0xA5, name: "LDA", bytes: 2, addressing_mode: AddressingMode::ZeroPage},
         Instruction {opcode: 0xB5, name: "LDA", bytes: 2, addressing_mode: AddressingMode::ZeroPage_X},

src/cpu/mod.rs

@@ -101,6 +101,10 @@ impl CPU {
                 self.bpl();
                 None
             }
+            "BVC" => {
+                self.bvc();
+                None
+            }
             "BRK" => Some(0),
             "LDA" => {
                 self.lda(&instruction.addressing_mode);
@@ -366,6 +370,19 @@ impl CPU {
         }
     }
 
+    fn bvc (&mut self) {
+        match self.get_flag_state(STATUS_FLAG_MASK_OVERFLOW) {
+            FlagStates::CLEAR => {
+                let distance = self.mem_read(self.program_counter);
+                self.program_counter =
+                    self.branch_off_program_counter(self.program_counter, distance as u16);
+            }
+            FlagStates::SET => {
+                return;
+            }
+        }
+    }
+
     fn lda(&mut self, addressing_mode: &AddressingMode) {
         let operand = self.get_operand(addressing_mode);
         self.register_a = operand;
@@ -646,15 +663,15 @@ mod test_cpu {
         assert_eq!(cpu.program_counter, expected_program_counter);
     }
 
-    #[test_case(0b1000_0000, 0x8080, 0x8080, 0x06)]
+    #[test_case(0b0100_0000, 0x8080, 0x8080, 0x06)]
     #[test_case(0b0000_0000, 0xE004, 0xE009, 0x06)]
     #[test_case(0b0000_0000, 0xE009, 0xE003, 0xFA)]
-    fn test_bpl(status: u8, program_counter: u16, expected_program_counter: u16, distance: u8) {
+    fn test_bvc(status: u8, program_counter: u16, expected_program_counter: u16, distance: u8) {
         let mut cpu = CPU::new();
         cpu.status = status;
         cpu.program_counter = program_counter;
         cpu.memory[cpu.program_counter as usize] = distance;
-        cpu.bpl();
+        cpu.bvc();
         assert_eq!(cpu.program_counter, expected_program_counter);
     }