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Implement the DEC instruction.

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This commit is contained in:
Andrew Keeton 2014-10-19 21:20:19 -04:00
parent 6d7388c779
commit 2a78062b12
1 changed files with 55 additions and 3 deletions
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54
src/machine.rs
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@ -29,7 +29,7 @@ use log;
use std;
use address::{AddressDiff};
use address::{Address, AddressDiff};
use instruction;
use instruction::{DecodedInstr};
use memory::Memory;
@ -90,6 +90,10 @@ impl Machine {
self.add_with_carry(val);
},
(instruction::DEC, instruction::UseAddress(addr)) => {
self.decrement_memory(addr)
}
(instruction::DEX, instruction::UseImplied) => {
self.dec_x();
}
@ -204,6 +208,24 @@ impl Machine {
log!(log::DEBUG, "accumulator: {}", self.registers.accumulator);
}
pub fn decrement_memory(&mut self, addr: Address) {
let value_new = self.memory.get_byte(addr) - 1;
self.memory.set_byte(addr, value_new);
let is_negative = (value_new as i8) < 0;
let is_zero = value_new == 0;
self.registers.status.set_with_mask(
PS_NEGATIVE | PS_ZERO,
Status::new(StatusArgs {
negative: is_negative,
zero: is_zero,
..StatusArgs::none()
})
);
}
pub fn dec_x(&mut self) {
let val = self.registers.index_x;
self.load_x_register(val - 1);
@ -291,6 +313,36 @@ fn add_with_carry_test() {
assert_eq!(machine.registers.status.contains(PS_OVERFLOW), true);
}
#[test]
fn decrement_memory_test() {
let mut machine = Machine::new();
let addr = Address(0xA1B2);
machine.memory.set_byte(addr, 5);
machine.decrement_memory(addr);
assert_eq!(machine.memory.get_byte(addr), 4);
assert_eq!(machine.registers.status.contains(PS_ZERO), false);
assert_eq!(machine.registers.status.contains(PS_NEGATIVE), false);
machine.decrement_memory(addr);
assert_eq!(machine.memory.get_byte(addr), 3);
assert_eq!(machine.registers.status.contains(PS_ZERO), false);
assert_eq!(machine.registers.status.contains(PS_NEGATIVE), false);
machine.decrement_memory(addr);
machine.decrement_memory(addr);
machine.decrement_memory(addr);
assert_eq!(machine.memory.get_byte(addr), 0);
assert_eq!(machine.registers.status.contains(PS_ZERO), true);
assert_eq!(machine.registers.status.contains(PS_NEGATIVE), false);
machine.decrement_memory(addr);
assert_eq!(machine.memory.get_byte(addr) as i8, -1);
assert_eq!(machine.registers.status.contains(PS_ZERO), false);
assert_eq!(machine.registers.status.contains(PS_NEGATIVE), true);
}
#[test]
fn dec_x_test() {
let mut machine = Machine::new();