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Reduce code for u8 byte read #342

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Reduce code for u8 byte read #342

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49 changes: 7 additions & 42 deletions src/impls/primitive.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,54 +9,19 @@ use alloc::format;
impl DekuRead<'_, (Endian, ByteSize)> for u8 {
fn read(
input: &BitSlice<u8, Msb0>,
(_, size): (Endian, ByteSize),
(_, _): (Endian, ByteSize),
) -> Result<(&BitSlice<u8, Msb0>, Self), DekuError> {
const MAX_TYPE_BITS: usize = BitSize::of::<u8>().0;
let bit_size: usize = size.0 * 8;

// TODO
// if they never give [bits] or [bytes] we don't need to check the size
if bit_size > MAX_TYPE_BITS {
return Err(DekuError::Parse(format!(
"too much data: container of {MAX_TYPE_BITS} bits cannot hold {bit_size} bits",
if input.len() < MAX_TYPE_BITS {
return Err(DekuError::Incomplete(crate::error::NeedSize::new(
MAX_TYPE_BITS,
)));
}

if input.len() < bit_size {
return Err(DekuError::Incomplete(crate::error::NeedSize::new(bit_size)));
}

let (bit_slice, rest) = input.split_at(bit_size);
let pad = 8 * ((bit_slice.len() + 7) / 8) - bit_slice.len();

let value = if pad == 0
&& bit_slice.len() == MAX_TYPE_BITS
&& bit_slice.domain().region().unwrap().1.len() * 8 == MAX_TYPE_BITS
{
// if everything is aligned, just read the value
bit_slice.load::<u8>()
} else {
let mut bits: BitVec<u8, Msb0> = BitVec::with_capacity(bit_slice.len() + pad);

// Copy bits to new BitVec
bits.extend_from_bitslice(bit_slice);

// Force align
//i.e. [1110, 10010110] -> [11101001, 0110]
bits.force_align();

let bytes: &[u8] = bits.as_raw_slice();

// cannot use from_X_bytes as we don't have enough bytes for $typ
// read manually
let mut res: u8 = 0;
for b in bytes.iter().rev() {
res |= *b;
}

res
};
// SAFETY: We already check that input.len() < bit_size above
let (bit_slice, rest) = unsafe { input.split_at_unchecked(MAX_TYPE_BITS) };

let value = bit_slice.load::<u8>();
Ok((rest, value))
}
}
Expand Down