cpubits: add 16 vs 32 and 32 vs 64-bit patterns

For use cases where one of the three sizes won't be supported (either
16-bit or 64-bit), allows matching against only two of the three options

Author: tarcieri

cpubits/src/lib.rs

@@ -197,6 +197,30 @@ macro_rules! cpubits {
         }
     };
 
+    // Select between 16-bit and 32-bit options, where no code will be generated for 64-bit targets
+    (
+        16 => { $( $tokens16:tt )* }
+        32 => { $( $tokens32:tt )* }
+    ) => {
+        $crate::cpubits! {
+            16 => { $( $tokens16 )* }
+            32 => { $( $tokens32 )* }
+            64 => { }
+        }
+    };
+
+    // Select between 32-bit and 64-bit options, where no code will be generated for 16-bit targets
+    (
+        32 => { $( $tokens32:tt )* }
+        64 => { $( $tokens64:tt )* }
+    ) => {
+        $crate::cpubits! {
+            16 => { }
+            32 => { $( $tokens32 )* }
+            64 => { $( $tokens64 )* }
+        }
+    };
+
     // Select between 16-bit and 32-bit options, where 64-bit will use the 32-bit option
     (
         16 => { $( $tokens16:tt )* }