Add conditional relative jumps

src/cpu/instructions/control.rs

@@ -33,6 +33,12 @@ pub enum ControlFlowInstruction {
         offset: i8,
     },
 
+    JumpRelativeIfFlagMatches {
+        flag: register::Flag,
+        value: u8,
+        offset: i8,
+    },
+
     Return,
 
     ReturnAndEnableInterrupts,

src/cpu/parse/control.rs

@@ -14,6 +14,7 @@ pub struct Parser;
 enum ConditionalControlFlowType {
     Call,
     Jump,
+    RelativeJump,
     Return,
 }
 
@@ -34,11 +35,11 @@ fn parse_unconditional_control_operation(data: &View) -> ParseResult {
 fn parse_unconditional_parameterized_control_flow_operation(data: &View) -> ParseResult {
     let opcode = parse::get_opcode_from_data(data);
     match opcode {
-        0xC3 => Ok(build_immediate_parameterized_control_flow_data(
+        0xC3 => Ok(build_immediate_addr_parameterized_control_flow_data(
             data,
             |addr| ControlFlowInstruction::JumpToImmediate { addr },
         )),
-        0xCD => Ok(build_immediate_parameterized_control_flow_data(
+        0xCD => Ok(build_immediate_addr_parameterized_control_flow_data(
             data,
             |addr| ControlFlowInstruction::Call { addr },
         )),
@@ -93,14 +94,19 @@ fn parse_conditional_control_operation(data: &View) -> ParseResult {
     let (flag, value) = conditional_control_flow_flag_for_opcode(opcode)?;
     let control_flow_type = conditional_control_flow_type_for_opcode(opcode)?;
     match control_flow_type {
-        ConditionalControlFlowType::Jump => Ok(build_immediate_parameterized_control_flow_data(
-            data,
-            |addr| ControlFlowInstruction::JumpToImmediateIfFlagMatches { flag, value, addr },
-        )),
-        ConditionalControlFlowType::Call => Ok(build_immediate_parameterized_control_flow_data(
-            data,
-            |addr| ControlFlowInstruction::CallIfFlagMatches { flag, value, addr },
-        )),
+        ConditionalControlFlowType::Jump => Ok(
+            build_immediate_addr_parameterized_control_flow_data(data, |addr| {
+                ControlFlowInstruction::JumpToImmediateIfFlagMatches { flag, value, addr }
+            }),
+        ),
+        ConditionalControlFlowType::Call => Ok(
+            build_immediate_addr_parameterized_control_flow_data(data, |addr| {
+                ControlFlowInstruction::CallIfFlagMatches { flag, value, addr }
+            }),
+        ),
+        ConditionalControlFlowType::RelativeJump => {
+            Ok(build_conditional_jump_relative_data(data, flag, value))
+        }
         ConditionalControlFlowType::Return => Ok((
             Instruction::ControlFlow(ControlFlowInstruction::ReturnIfFlagMatches { flag, value }),
             1,
@@ -115,21 +121,22 @@ fn conditional_control_flow_type_for_opcode(
         0xC2 | 0xD2 | 0xCA | 0xDA => Ok(ConditionalControlFlowType::Jump),
         0xC4 | 0xD4 | 0xCC | 0xDC => Ok(ConditionalControlFlowType::Call),
         0xC0 | 0xD0 | 0xC8 | 0xD8 => Ok(ConditionalControlFlowType::Return),
+        0x20 | 0x30 | 0x28 | 0x38 => Ok(ConditionalControlFlowType::RelativeJump),
         _ => Err(parse::Error::UnknownOpcode(opcode)),
     }
 }
 
 fn conditional_control_flow_flag_for_opcode(opcode: u8) -> Result<(Flag, u8), parse::Error> {
     match opcode {
-        0xC0 | 0xC2 | 0xC4 => Ok((Flag::Zero, 0)),
-        0xD0 | 0xD2 | 0xD4 => Ok((Flag::Carry, 0)),
-        0xC8 | 0xCA | 0xCC => Ok((Flag::Zero, 1)),
-        0xD8 | 0xDA | 0xDC => Ok((Flag::Carry, 1)),
+        0xC0 | 0xC2 | 0xC4 | 0x20 => Ok((Flag::Zero, 0)),
+        0xD0 | 0xD2 | 0xD4 | 0x30 => Ok((Flag::Carry, 0)),
+        0xC8 | 0xCA | 0xCC | 0x28 => Ok((Flag::Zero, 1)),
+        0xD8 | 0xDA | 0xDC | 0x38 => Ok((Flag::Carry, 1)),
         _ => Err(parse::Error::UnknownOpcode(opcode)),
     }
 }
 
-fn build_immediate_parameterized_control_flow_data<F: Fn(u16) -> ControlFlowInstruction>(
+fn build_immediate_addr_parameterized_control_flow_data<F: Fn(u16) -> ControlFlowInstruction>(
     data: &View,
     make_variant: F,
 ) -> ParseOutput {
@@ -139,3 +146,15 @@ fn build_immediate_parameterized_control_flow_data<F: Fn(u16) -> ControlFlowInst
 
     (Instruction::ControlFlow(make_variant(addr)), 3)
 }
+
+fn build_conditional_jump_relative_data(data: &View, flag: Flag, flag_value: u8) -> ParseOutput {
+    let (_opcode, offset) = data.get_tuple();
+
+    let ins = Instruction::ControlFlow(ControlFlowInstruction::JumpRelativeIfFlagMatches {
+        flag,
+        value: flag_value,
+        offset: i8::from_be_bytes([offset]),
+    });
+
+    (ins, 2)
+}

src/cpu/run/arithutil.rs

@@ -171,6 +171,7 @@ impl CarryingSub<CarriedNumber<u8>> for u8 {
     }
 }
 
+
 /// `did_8_bit_add_half_carry` checks whether or not the given addition would have done an 8 bit half carry.
 // NOTE: These generics are not as generic as they could be. The Into<u16> is just a shortcut because we
 //       only use up to u16s

src/cpu/run/control.rs

@@ -81,18 +81,22 @@ impl Run for ControlFlowInstruction {
             }
 
             Self::JumpRelative { offset } => {
-                let current_pc = processor
-                    .registers
-                    .get_single_16bit_register(register::SingleSixteenBit::ProgramCounter);
-
-                // We don't need the flags, but this trait does the propper adding for us
-                // TODO: Break this out into its own arithutil function?
-                let (updated_pc, _half_carry, _carry) = current_pc.add_with_carry(offset);
-
-                jump_to(processor, updated_pc);
-
+                do_relative_jump(processor, offset);
                 Ok(Cycles(12))
             }
+
+            Self::JumpRelativeIfFlagMatches {
+                flag,
+                value,
+                offset,
+            } => {
+                if processor.registers.get_flag_bit(flag) == value {
+                    do_relative_jump(processor, offset);
+                    Ok(Cycles(12))
+                } else {
+                    Ok(Cycles(8))
+                }
+            }
         }
     }
 }
@@ -115,6 +119,18 @@ fn jump_to(processor: &mut Processor, to_addr: u16) {
         .set_single_16bit_register(register::SingleSixteenBit::ProgramCounter, to_addr);
 }
 
+fn do_relative_jump(processor: &mut Processor, offset: i8) {
+    let current_pc = processor
+        .registers
+        .get_single_16bit_register(register::SingleSixteenBit::ProgramCounter);
+
+    // We don't need the flags, but this trait does the propper adding for us
+    // TODO: Break this out into its own arithutil function?
+    let (updated_pc, _half_carry, _carry) = current_pc.add_with_carry(offset);
+
+    jump_to(processor, updated_pc);
+}
+
 fn return_to_popped_addr(processor: &mut Processor) -> Result<(), super::Error> {
     processor.pop_from_stack_to_16bit_register(register::SingleSixteenBit::ProgramCounter.into())
 }

tests/cpu/control.rs

@@ -2,7 +2,7 @@ use ferris_boi::{
     cpu::{instructions::Instruction, Processor},
     register::{self, Flag},
 };
-use test_case::test_case;
+use test_case::{test_case, test_matrix};
 
 #[test]
 fn test_can_jump_to_immediate() {
@@ -232,6 +232,68 @@ fn test_jump_relative_jumps_by_the_given_number_of_bytes(distance: i8) {
     assert_eq!(expected_pc, processor.registers.program_counter);
 }
 
+#[test_matrix(
+    [
+        (0x20, Flag::Zero, 0),
+        (0x30, Flag::Carry, 0),
+        (0x28, Flag::Zero, 1),
+        (0x38, Flag::Carry, 1),
+    ],
+    [10, 0, -8]
+)]
+fn test_jump_relative_jumps_by_the_given_number_of_bytes_if_condition_matches(
+    (opcode, flag, flag_value): (u8, Flag, u8),
+    distance: i8,
+) {
+    let mut processor = Processor::default();
+    processor.registers.set_flag_bit(flag, flag_value);
+
+    let starting_pc = processor.registers.program_counter;
+    let data = [opcode, i8::to_be_bytes(distance)[0], 0x06];
+    let (ins, extra_data) = Instruction::from_data(&data).expect("could not parse instruction");
+
+    assert_eq!(extra_data, &[0x06]);
+
+    processor.run_instruction(ins);
+    let expected_pc = if distance > 0 {
+        starting_pc + u16::from(distance.unsigned_abs())
+    } else {
+        starting_pc - u16::from(distance.unsigned_abs())
+    };
+
+    assert_eq!(expected_pc, processor.registers.program_counter);
+}
+
+#[test_matrix(
+    [
+        (0x20, Flag::Zero, 0),
+        (0x30, Flag::Carry, 0),
+        (0x28, Flag::Zero, 1),
+        (0x38, Flag::Carry, 1),
+    ],
+    [10, 0, -8]
+)]
+fn test_jump_relative_does_nothing_if_condition_does_not_match(
+    (opcode, flag, flag_value): (u8, Flag, u8),
+    distance: i8,
+) {
+    let mut processor = Processor::default();
+    processor
+        .registers
+        .set_flag_bit(flag, if flag_value == 0 { 1 } else { 0 });
+
+    let starting_pc = processor.registers.program_counter;
+    let data = [opcode, i8::to_be_bytes(distance)[0], 0x06];
+    let (ins, extra_data) = Instruction::from_data(&data).expect("could not parse instruction");
+
+    assert_eq!(extra_data, &[0x06]);
+
+    processor.run_instruction(ins);
+
+    // Would normally advance, but run_instruction does not advance PC
+    assert_eq!(starting_pc, processor.registers.program_counter);
+}
+
 #[test_case(0xC9; "RET")]
 #[test_case(0xD9; "RETI")]
 fn test_ret_jumps_to_address_on_stack(opcode: u8) {