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#[derive(Default, Debug, PartialEq)]
pub struct Flags {
pub z: bool,
pub s: bool,
pub p: bool,
pub cy: bool,
pub ac: bool,
}
impl Flags {
pub fn from_processor_status_word(psw: u8) -> Flags {
Flags {
z: (psw & (1 << 6)) != 0,
s: (psw & (1 << 7)) != 0,
p: (psw & (1 << 2)) != 0,
cy: (psw & 1) != 0,
ac: (psw & (1 << 4)) != 0,
}
}
pub fn set_flags_for(&mut self, operand1: u8, result: i16) {
self.z = (result as u8) == 0;
self.s = (result & 0x0080) != 0;
self.p = Flags::parity(result as u8);
self.cy = (result as u16 & 0xff00) != 0;
self.ac = (operand1 & 0x000f) + ((result.wrapping_sub(operand1 as i16)) & 0x000f) as u8 > 0x0f;
}
pub fn set_flags_except_carry_for(&mut self, operand1: u8, result: i16) {
self.z = (result as u8) == 0;
self.s = (result & 0x0080) != 0;
self.p = Flags::parity(result as u8);
self.ac = (operand1 & 0x000f) + ((result.wrapping_sub(operand1 as i16)) & 0x000f) as u8 > 0x0f;
}
pub fn to_processor_status_word(&self) -> u8 {
(self.cy as u8)
+ 2
+ ((self.p as u8) << 2)
+ ((self.ac as u8) << 4)
+ ((self.z as u8) << 6)
+ ((self.s as u8) << 7)
}
fn parity(mut value: u8) -> bool {
value ^= value >> 4;
value ^= value >> 2;
value ^= value >> 1;
(value & 1) == 0
}
}
#[cfg(test)]
mod tests {
use super::Flags;
#[test]
fn flags_non_zero_sign_pair_ac() {
let mut flags: Flags = Default::default();
flags.set_flags_for(0x0f, 0x96);
assert_eq!(flags.z, false);
assert_eq!(flags.s, true);
assert_eq!(flags.p, true);
assert_eq!(flags.cy, false);
assert_eq!(flags.ac, true);
}
#[test]
fn flags_zero() {
let mut flags: Flags = Default::default();
flags.set_flags_for(0, 0);
assert_eq!(flags.z, true);
assert_eq!(flags.s, false);
assert_eq!(flags.p, true);
assert_eq!(flags.cy, false);
assert_eq!(flags.ac, false);
}
#[test]
fn flags_carry() {
let mut flags: Flags = Default::default();
flags.set_flags_for(0, 0x0101);
assert_eq!(flags.z, false);
assert_eq!(flags.s, false);
assert_eq!(flags.p, false);
assert_eq!(flags.cy, true);
assert_eq!(flags.ac, false);
}
#[test]
fn flags_underflow() {
let mut flags: Flags = Default::default();
flags.set_flags_for(0, -0x0012);
assert_eq!(flags.z, false);
assert_eq!(flags.s, true);
assert_eq!(flags.p, true);
assert_eq!(flags.cy, true);
assert_eq!(flags.ac, false);
}
}