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Implement the DEC instruction.
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6d7388c779
commit
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@ -29,7 +29,7 @@ use log;
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use std;
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use address::{AddressDiff};
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use address::{Address, AddressDiff};
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use instruction;
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use instruction::{DecodedInstr};
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use memory::Memory;
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@ -90,6 +90,10 @@ impl Machine {
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self.add_with_carry(val);
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},
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(instruction::DEC, instruction::UseAddress(addr)) => {
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self.decrement_memory(addr)
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}
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(instruction::DEX, instruction::UseImplied) => {
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self.dec_x();
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}
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@ -204,6 +208,24 @@ impl Machine {
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log!(log::DEBUG, "accumulator: {}", self.registers.accumulator);
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}
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pub fn decrement_memory(&mut self, addr: Address) {
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let value_new = self.memory.get_byte(addr) - 1;
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self.memory.set_byte(addr, value_new);
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let is_negative = (value_new as i8) < 0;
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let is_zero = value_new == 0;
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self.registers.status.set_with_mask(
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PS_NEGATIVE | PS_ZERO,
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Status::new(StatusArgs {
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negative: is_negative,
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zero: is_zero,
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..StatusArgs::none()
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})
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);
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}
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pub fn dec_x(&mut self) {
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let val = self.registers.index_x;
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self.load_x_register(val - 1);
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@ -291,6 +313,36 @@ fn add_with_carry_test() {
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assert_eq!(machine.registers.status.contains(PS_OVERFLOW), true);
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}
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#[test]
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fn decrement_memory_test() {
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let mut machine = Machine::new();
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let addr = Address(0xA1B2);
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machine.memory.set_byte(addr, 5);
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machine.decrement_memory(addr);
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assert_eq!(machine.memory.get_byte(addr), 4);
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assert_eq!(machine.registers.status.contains(PS_ZERO), false);
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assert_eq!(machine.registers.status.contains(PS_NEGATIVE), false);
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machine.decrement_memory(addr);
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assert_eq!(machine.memory.get_byte(addr), 3);
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assert_eq!(machine.registers.status.contains(PS_ZERO), false);
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assert_eq!(machine.registers.status.contains(PS_NEGATIVE), false);
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machine.decrement_memory(addr);
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machine.decrement_memory(addr);
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machine.decrement_memory(addr);
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assert_eq!(machine.memory.get_byte(addr), 0);
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assert_eq!(machine.registers.status.contains(PS_ZERO), true);
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assert_eq!(machine.registers.status.contains(PS_NEGATIVE), false);
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machine.decrement_memory(addr);
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assert_eq!(machine.memory.get_byte(addr) as i8, -1);
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assert_eq!(machine.registers.status.contains(PS_ZERO), false);
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assert_eq!(machine.registers.status.contains(PS_NEGATIVE), true);
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}
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#[test]
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fn dec_x_test() {
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let mut machine = Machine::new();
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