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cleanup reading a bit

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This commit is contained in:
Robin Appelman 2019-02-17 23:08:20 +01:00
commit 348fbb851b
1 changed files with 5 additions and 21 deletions
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26
src/lib.rs
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@ -1,4 +1,5 @@
#![feature(test)]
#![feature(try_from)]
#![warn(missing_docs)]
//! Tools for reading integers of arbitrary bit length and non byte-aligned integers and other data types
@ -44,23 +45,6 @@ pub struct BitBuffer<'a> {
byte_len: usize,
}
macro_rules! array_ref {
($arr:expr, $offset:expr, $len:expr) => {{
{
#[inline]
unsafe fn as_array<T>(slice: &[T]) -> &[T; $len] {
&*(slice.as_ptr() as *const [_; $len])
}
let offset = $offset;
let slice = & $arr[offset..offset + $len];
#[allow(unused_unsafe)]
unsafe {
as_array(slice)
}
}
}}
}
const USIZE_SIZE: usize = size_of::<usize>();
impl<'a> BitBuffer<'a> {
@ -121,11 +105,11 @@ impl<'a> BitBuffer<'a> {
}
let byte_index = position / 8;
let bit_offset = position & 7;
let bytes: &[u8; USIZE_SIZE] = array_ref!(self.bytes, byte_index, USIZE_SIZE);
let container_le = unsafe {
std::mem::transmute::<[u8; USIZE_SIZE], usize>(*bytes)
let slice = &self.bytes[byte_index..byte_index + USIZE_SIZE];
let bytes: [u8; USIZE_SIZE] = unsafe {
*(slice.as_ptr() as *const [u8; USIZE_SIZE])
};
let container = usize::from_le(container_le);
let container = usize::from_le_bytes(bytes);
let shifted = container >> bit_offset;
let mask = !(usize::max_value() << count);
Ok(shifted & mask)