thermostat/src/ad7172/checksum.rs

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#[derive(Clone, Copy, PartialEq)]
#[repr(u8)]
pub enum ChecksumMode {
Off = 0b00,
/// Seems much less reliable than `Crc`
Xor = 0b01,
Crc = 0b10,
}
impl From<u8> for ChecksumMode {
fn from(x: u8) -> Self {
match x {
0 => ChecksumMode::Off,
1 => ChecksumMode::Xor,
_ => ChecksumMode::Crc,
}
}
}
pub struct Checksum {
mode: ChecksumMode,
state: u8,
}
impl Checksum {
pub fn new(mode: ChecksumMode) -> Self {
Checksum { mode, state: 0 }
}
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fn feed_byte(&mut self, input: u8) {
match self.mode {
ChecksumMode::Off => {},
ChecksumMode::Xor => self.state ^= input,
ChecksumMode::Crc => {
for i in 0..8 {
let input_mask = 0x80 >> i;
self.state = (self.state << 1) ^
if ((self.state & 0x80) != 0) != ((input & input_mask) != 0) {
0x07 /* x8 + x2 + x + 1 */
} else {
0
};
}
}
}
}
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pub fn feed(&mut self, input: &[u8]) {
for &b in input {
self.feed_byte(b);
}
}
pub fn result(&self) -> Option<u8> {
match self.mode {
ChecksumMode::Off => None,
_ => Some(self.state)
}
}
}