Implement as_ne_bytes for floats and integers

library/core/src/num/int_macros.rs

@@ -2054,6 +2054,41 @@ assert_eq!(
             }
         }
 
+        doc_comment! {
+            concat!("
+Return the memory representation of this integer as a byte array in
+native byte order.
+
+[`to_ne_bytes`] should be preferred over this whenever possible.
+
+[`to_ne_bytes`]: #method.to_ne_bytes
+",
+
+"
+# Examples
+
+```
+#![feature(num_as_ne_bytes)]
+let num = ", $swap_op, stringify!($SelfT), ";
+let bytes = num.as_ne_bytes();
+assert_eq!(
+    bytes,
+    if cfg!(target_endian = \"big\") {
+        &", $be_bytes, "
+    } else {
+        &", $le_bytes, "
+    }
+);
+```"),
+            #[unstable(feature = "num_as_ne_bytes", issue = "76976")]
+            #[inline]
+            pub fn as_ne_bytes(&self) -> &[u8; mem::size_of::<Self>()] {
+                // SAFETY: integers are plain old datatypes so we can always transmute them to
+                // arrays of bytes
+                unsafe { &*(self as *const Self as *const _) }
+            }
+        }
+
 doc_comment! {
             concat!("Create an integer value from its representation as a byte array in
 big endian.