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dont read unalligned usize

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This commit is contained in:
Robin Appelman 2019-12-25 15:38:14 +01:00
commit 8147ae1988
1 changed files with 9 additions and 15 deletions
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24
src/buffer.rs
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@ -103,32 +103,26 @@ where
let bit_offset = position & 7;
let usize_bit_size = size_of::<usize>() * 8;
let container = if cfg!(feature = "unsafe") {
let bytes: [u8; USIZE_SIZE] = if cfg!(feature = "unsafe") {
use std::mem::transmute;
// panic instead of accessing out of bounds data when the caller didn't do it's job bounds checking
// due to the magic of branch prediction and this check "always" passing, the cost for this
// is below the point of being measurable by `cargo bench`
assert!(position + count <= self.bit_len());
let raw_container: &usize = unsafe {
unsafe {
// this is safe here because we already have checks that we don't read past the slice
let ptr = self.bytes.as_ptr().add(byte_index);
transmute(ptr)
};
if E::is_le() {
usize::from_le(*raw_container)
} else {
usize::from_be(*raw_container)
*transmute::<_, &[u8; USIZE_SIZE]>(ptr)
}
} else {
let bytes = self.read_usize_bytes(byte_index);
self.read_usize_bytes(byte_index)
};
if E::is_le() {
usize::from_le_bytes(bytes)
} else {
usize::from_be_bytes(bytes)
}
let container = if E::is_le() {
usize::from_le_bytes(bytes)
} else {
usize::from_be_bytes(bytes)
};
let shifted = if E::is_le() {