6502/mre-mos6502
1
0
Fork 0
mirror of https://github.com/mre/mos6502.git synced 2024-11-28 22:51:26 +00:00
Code Issues Projects Releases Wiki Activity

DEX instruction and test

Browse Source
This commit is contained in:
Alex Weisberger 2014-10-07 23:52:38 -04:00
parent 34cd5edd44
commit d132f040f2
1 changed files with 43 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
src/machine.rs
View File

@ -90,6 +90,10 @@ impl Machine {
self.add_with_carry(val);
},
(instruction::DEX, instruction::UseImplied) => {
self.dec_x();
}
(instruction::LDA, instruction::UseImmediate(val)) => {
log!(log::DEBUG, "load A immediate: {}", val);
self.load_accumulator(val as i8);
@ -199,6 +203,26 @@ impl Machine {
log!(log::DEBUG, "accumulator: {}", self.registers.accumulator);
}
pub fn dec_x(&mut self) {
let x_before = self.registers.index_x;
let value = 1i8;
let x_after = x_before - value;
self.registers.index_x = x_before - 1;
let is_negative = x_after < 0;
let is_zero = x_after == 0;
let mask = ps_negative | ps_zero;
self.registers.status.set_with_mask(
mask,
Status::new(StatusArgs {
negative: is_negative,
zero: is_zero,
..StatusArgs::none()
})
);
}
}
impl std::fmt::Show for Machine {
@ -281,3 +305,22 @@ fn add_with_carry_test() {
assert_eq!(machine.registers.status.contains(PS_NEGATIVE), true);
assert_eq!(machine.registers.status.contains(PS_OVERFLOW), true);
}
#[test]
fn dec_x_test() {
let mut machine = Machine::new();
machine.dec_x();
assert_eq!(machine.registers.index_x, -1);
assert_eq!(machine.registers.status.contains(ps_carry), false);
assert_eq!(machine.registers.status.contains(ps_zero), false);
assert_eq!(machine.registers.status.contains(ps_negative), true);
assert_eq!(machine.registers.status.contains(ps_overflow), false);
machine.dec_x();
assert_eq!(machine.registers.index_x, -2);
assert_eq!(machine.registers.status.contains(ps_carry), false);
assert_eq!(machine.registers.status.contains(ps_zero), false);
assert_eq!(machine.registers.status.contains(ps_negative), true);
assert_eq!(machine.registers.status.contains(ps_overflow), false);
}