reduce bound checks

heed/src/reserved_space.rs

@@ -111,17 +111,17 @@ impl io::Write for ReservedSpace<'_> {
 
  #[inline]
  fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
- let remaining = &mut self.bytes[self.write_head..];
+ let remaining = unsafe { self.bytes.get_unchecked_mut(self.write_head..) };
 
  if buf.len() > remaining.len() {
  return Err(io::Error::from(io::ErrorKind::WriteZero));
  }
 
- // SAFETY: we can always cast `T` -> `MaybeUninit<T>` as it's a transparent wrapper
- let buf_uninit: &[std::mem::MaybeUninit<u8>] =
- unsafe { std::slice::from_raw_parts(buf.as_ptr().cast(), buf.len()) };
-
- remaining[..buf.len()].copy_from_slice(buf_uninit);
+ unsafe {
+  // SAFETY: we can always cast `T` -> `MaybeUninit<T>` as it's a transparent wrapper
+ let buf_uninit = std::slice::from_raw_parts(buf.as_ptr().cast(), buf.len());
+ remaining.get_unchecked_mut(..buf.len()).copy_from_slice(buf_uninit);
+ }
 
  self.write_head += buf.len();
  self.written = usize::max(self.written, self.write_head);