Prevent potential bitwise operations issue (#1309)

* fix: potential bitwise operations issue

* fix: comment

docs/modules/ROOT/pages/api/utilities.adoc

@@ -174,7 +174,7 @@ Module containing math utilities.
 [[math-average]]
 ==== `[.contract-item-name]#++average++#++(a: T, b: T) → T++` [.item-kind]#function#
 
-Returns the average of two values. The result is rounded down.
+Returns the average of two unsigned integers. The result is rounded down.
 
 NOTE: `T` is a generic value matching different numeric implementations.
 

packages/utils/src/math.cairo

@@ -3,19 +3,22 @@
 
 use core::traits::{BitAnd, BitXor, Into};
 
-/// Returns the average of two numbers. The result is rounded down.
+/// Returns the average of two unsigned integers. The result is rounded down.
 pub fn average<
-    T,
-    impl TDrop: Drop<T>,
-    impl TCopy: Copy<T>,
-    impl TAdd: Add<T>,
-    impl TDiv: Div<T>,
-    impl TBitAnd: BitAnd<T>,
-    impl TBitXor: BitXor<T>,
-    impl TInto: Into<u8, T>,
+    T, +Unsigned<T>, +Add<T>, +Div<T>, +BitAnd<T>, +BitXor<T>, +Into<u8, T>, +Copy<T>, +Drop<T>,
 >(
     a: T, b: T,
 ) -> T {
     // (a + b) / 2 can overflow.
     (a & b) + (a ^ b) / 2_u8.into()
 }
+
+/// A trait to represent unsigned integers.
+pub trait Unsigned<T>;
+
+impl U8Unsigned of Unsigned<u8>;
+impl U16Unsigned of Unsigned<u16>;
+impl U32Unsigned of Unsigned<u32>;
+impl U64Unsigned of Unsigned<u64>;
+impl U128Unsigned of Unsigned<u128>;
+impl U256Unsigned of Unsigned<u256>;