Implement array sizes in the 16-bit index range

src/array.rs

@@ -4,6 +4,9 @@ pub unsafe trait Array {
     /// The array's element type
     type Item;
     #[doc(hidden)]
+    /// The smallest index type that indexes the array.
+    type Index: Index;
+    #[doc(hidden)]
     fn as_ptr(&self) -> *const Self::Item;
     #[doc(hidden)]
     fn as_mut_ptr(&mut self) -> *mut Self::Item;
@@ -11,10 +14,29 @@ pub unsafe trait Array {
     fn capacity() -> usize;
 }
 
+pub trait Index : PartialEq + Copy {
+    fn zero() -> Self;
+    fn to_usize(self) -> usize;
+    fn from(usize) -> Self;
+}
+
+impl Index for u8 {
+    fn zero() -> Self { 0 }
+    fn to_usize(self) -> usize { self as usize }
+    fn from(ix: usize) ->  Self { ix as u8 }
+}
+
+impl Index for u16 {
+    fn zero() -> Self { 0 }
+    fn to_usize(self) -> usize { self as usize }
+    fn from(ix: usize) ->  Self { ix as u16 }
+}
+
 macro_rules! fix_array_impl {
-    ($len:expr ) => (
+    ($index_type:ty, $len:expr ) => (
         unsafe impl<T> Array for [T; $len] {
             type Item = T;
+            type Index = $index_type;
             #[inline(always)]
             fn as_ptr(&self) -> *const T { self as *const _ as *const _ }
             #[inline(always)]
@@ -26,14 +48,15 @@ macro_rules! fix_array_impl {
 }
 
 macro_rules! fix_array_impl_recursive {
-    () => ();
-    ($len:expr, $($more:expr,)*) => (
-        fix_array_impl!($len);
-        fix_array_impl_recursive!($($more,)*);
+    ($index_type:ty, ) => ();
+    ($index_type:ty, $len:expr, $($more:expr,)*) => (
+        fix_array_impl!($index_type, $len);
+        fix_array_impl_recursive!($index_type, $($more,)*);
     );
 }
 
-fix_array_impl_recursive!(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+fix_array_impl_recursive!(u8, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
                           16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
                           32, 40, 48, 56, 64, 72, 96, 128, 160, 192, 224,);
+fix_array_impl_recursive!(u16, 256, 384, 512, 768, 1024, 2048, 4096, 8192, 16384, 32768,);