/// A trait for working with structs as little-endian byte arrays. Automatically
/// implemented for all built-in signed/unsigned integers.
pub trait LeBytes: Sized {
/// Write the memory representation of `self` as a byte array in
/// little-endian byte order into the provided buffer.
#[allow(clippy::wrong_self_convention)]
fn to_le_bytes(self, buf: &mut [u8]) -> Option<usize>;
/// Parse `self` from a byte array in little-endian byte order.
/// Returns None upon overflow.
fn from_le_bytes(buf: &[u8]) -> Option<Self>;
}
macro_rules! impl_to_le_bytes {
($($num:ty)*) => {
$(
impl LeBytes for $num {
fn to_le_bytes(self, buf: &mut [u8]) -> Option<usize> {
let len = core::mem::size_of::<$num>();
if buf.len() < len {
return None
}
buf[..len].copy_from_slice(&<$num>::to_le_bytes(self));
Some(len)
}
fn from_le_bytes(buf: &[u8]) -> Option<Self> {
let len = core::mem::size_of::<$num>();
let buf = if buf.len() > len {
let (extra, buf) = buf.split_at(buf.len() - len);
if extra.iter().any(|&b| b != 0) {
return None
}
buf
} else {
buf
};
let mut res: Self = 0;
for b in buf.iter().copied().rev() {
let b: Self = b as Self;
// `res <<= 8` causes the compiler to complain in the `u8` case
res <<= 4;
res <<= 4;
res |= b;
}
Some(res)
}
}
)*
};
}
impl_to_le_bytes!(u8 u16 u32 u64 u128 usize i8 i16 i32 i64 i128 isize);
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn basic() {
assert_eq!(
0x12345678,
LeBytes::from_le_bytes(&[0x78, 0x56, 0x34, 0x12]).unwrap()
)
}
#[test]
fn small() {
assert_eq!(
0x123456,
LeBytes::from_le_bytes(&[0x56, 0x34, 0x12]).unwrap()
)
}
#[test]
fn too_big() {
assert_eq!(
0x1234_u16,
LeBytes::from_le_bytes(&[0xde, 0xad, 0xbe, 0xef]).unwrap_or(0x1234)
)
}
}