Merge pull request gimli-rs#297 from philipc/issue-294

pod: add bytes_of_mut and bytes_of_slice_mut

src/pod.rs

@@ -114,6 +114,17 @@ pub fn bytes_of<T: Pod>(val: &T) -> &[u8] {
     unsafe { slice::from_raw_parts(slice::from_ref(val).as_ptr().cast(), size) }
 }
 
+/// Cast a `Pod` type to a mutable byte slice.
+#[inline]
+pub fn bytes_of_mut<T: Pod>(val: &mut T) -> &mut [u8] {
+    let size = mem::size_of::<T>();
+    // Safety:
+    // Any alignment is allowed.
+    // The size is determined in this function.
+    // The Pod trait ensures the type is valid to cast to bytes.
+    unsafe { slice::from_raw_parts_mut(slice::from_mut(val).as_mut_ptr().cast(), size) }
+}
+
 /// Cast a slice of a `Pod` type to a byte slice.
 #[inline]
 pub fn bytes_of_slice<T: Pod>(val: &[T]) -> &[u8] {
@@ -125,6 +136,17 @@ pub fn bytes_of_slice<T: Pod>(val: &[T]) -> &[u8] {
     unsafe { slice::from_raw_parts(val.as_ptr().cast(), size) }
 }
 
+/// Cast a slice of a `Pod` type to a mutable byte slice.
+#[inline]
+pub fn bytes_of_slice_mut<T: Pod>(val: &mut [T]) -> &mut [u8] {
+    let size = val.len().wrapping_mul(mem::size_of::<T>());
+    // Safety:
+    // Any alignment is allowed.
+    // The size is determined in this function.
+    // The Pod trait ensures the type is valid to cast to bytes.
+    unsafe { slice::from_raw_parts_mut(val.as_mut_ptr().cast(), size) }
+}
+
 /// A newtype for byte slices.
 ///
 /// It has these important features:
@@ -425,26 +447,41 @@ mod tests {
     #[test]
     fn single() {
         let x = u32::to_be(0x0123_4567);
+        let mut x_mut = x;
         let bytes = bytes_of(&x);
+        let bytes_mut = bytes_of_mut(&mut x_mut);
         assert_eq!(bytes, [0x01, 0x23, 0x45, 0x67]);
+        assert_eq!(bytes, bytes_mut);
 
         let x16 = [u16::to_be(0x0123), u16::to_be(0x4567)];
 
         let (y, tail) = from_bytes::<u32>(bytes).unwrap();
+        let (y_mut, tail_mut) = from_bytes_mut::<u32>(bytes_mut).unwrap();
         assert_eq!(*y, x);
+        assert_eq!(y, y_mut);
         assert_eq!(tail, &[]);
+        assert_eq!(tail, tail_mut);
 
         let (y, tail) = from_bytes::<u16>(bytes).unwrap();
+        let (y_mut, tail_mut) = from_bytes_mut::<u16>(bytes_mut).unwrap();
         assert_eq!(*y, x16[0]);
+        assert_eq!(y, y_mut);
         assert_eq!(tail, &bytes[2..]);
+        assert_eq!(tail, tail_mut);
 
         let (y, tail) = from_bytes::<u16>(&bytes[2..]).unwrap();
+        let (y_mut, tail_mut) = from_bytes_mut::<u16>(&mut bytes_mut[2..]).unwrap();
         assert_eq!(*y, x16[1]);
+        assert_eq!(y, y_mut);
         assert_eq!(tail, &[]);
+        assert_eq!(tail, tail_mut);
 
         assert_eq!(from_bytes::<u16>(&bytes[1..]), Err(()));
         assert_eq!(from_bytes::<u16>(&bytes[3..]), Err(()));
         assert_eq!(from_bytes::<u16>(&bytes[4..]), Err(()));
+        assert_eq!(from_bytes_mut::<u16>(&mut bytes_mut[1..]), Err(()));
+        assert_eq!(from_bytes_mut::<u16>(&mut bytes_mut[3..]), Err(()));
+        assert_eq!(from_bytes_mut::<u16>(&mut bytes_mut[4..]), Err(()));
     }
 
     #[test]
@@ -455,20 +492,33 @@ mod tests {
             u16::to_be(0x89ab),
             u16::to_be(0xcdef),
         ];
+        let mut x_mut = x;
+
         let bytes = bytes_of_slice(&x);
+        let bytes_mut = bytes_of_slice_mut(&mut x_mut);
         assert_eq!(bytes, [0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef]);
+        assert_eq!(bytes, bytes_mut);
 
-        let (y, tail) = slice_from_bytes::<u16>(&bytes, 4).unwrap();
+        let (y, tail) = slice_from_bytes::<u16>(bytes, 4).unwrap();
+        let (y_mut, tail_mut) = slice_from_bytes_mut::<u16>(bytes_mut, 4).unwrap();
         assert_eq!(y, x);
+        assert_eq!(y, y_mut);
         assert_eq!(tail, &[]);
+        assert_eq!(tail, tail_mut);
 
         let (y, tail) = slice_from_bytes::<u16>(&bytes[2..], 2).unwrap();
+        let (y_mut, tail_mut) = slice_from_bytes::<u16>(&mut bytes_mut[2..], 2).unwrap();
         assert_eq!(y, &x[1..3]);
+        assert_eq!(y, y_mut);
         assert_eq!(tail, &bytes[6..]);
+        assert_eq!(tail, tail_mut);
 
-        assert_eq!(slice_from_bytes::<u16>(&bytes, 5), Err(()));
+        assert_eq!(slice_from_bytes::<u16>(bytes, 5), Err(()));
         assert_eq!(slice_from_bytes::<u16>(&bytes[2..], 4), Err(()));
         assert_eq!(slice_from_bytes::<u16>(&bytes[1..], 2), Err(()));
+        assert_eq!(slice_from_bytes_mut::<u16>(bytes_mut, 5), Err(()));
+        assert_eq!(slice_from_bytes_mut::<u16>(&mut bytes_mut[2..], 4), Err(()));
+        assert_eq!(slice_from_bytes_mut::<u16>(&mut bytes_mut[1..], 2), Err(()));
     }
 
     #[test]