5.9 Right Shift Reverts on Bit Length Input

HerodotusDev · Oct 26, 2023 · 1cfbefb · 1cfbefb
1 parent 0eafd0c
commit 1cfbefb
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Showing 2 changed files with 12 additions and 3 deletions.
diff --git a/src/utils/bitwise.cairo b/src/utils/bitwise.cairo
@@ -29,18 +29,26 @@ fn left_shift<
 fn right_shift<
     T,
     impl TZeroable: Zeroable<T>,
+    impl TOneable: Oneable<T>,
     impl TAdd: Add<T>,
     impl TSub: Sub<T>,
-    impl TMul: Mul<T>,
     impl TDiv: Div<T>,
-    impl TOneable: Oneable<T>,
     impl TCopy: Copy<T>,
     impl TDrop: Drop<T>
 >(
     num: T, shift: T
 ) -> T {
+    let mut num = num;
+    let mut shift = shift;
     let two = TOneable::one() + TOneable::one();
-    num / pow(two, shift)
+
+    loop {
+        if shift.is_zero() {
+            break num;
+        }
+        num = num / two;
+        shift = shift - TOneable::one();
+    }
 }
 
 // @notice Bit length of a number

diff --git a/src/utils/tests/test_bitwise.cairo b/src/utils/tests/test_bitwise.cairo
@@ -20,6 +20,7 @@ fn test_right_shift() {
     assert(right_shift(256_u32, 8_u32) == 1, '256 >> 8');
     assert(right_shift(512_u32, 8_u32) == 2, '512 >> 8');
     assert(right_shift(65280_u32, 8_u32) == 255, '65280 >> 8');
+    assert(right_shift(128392_u32, 33_u32) == 0, '128392 >> 33');
 }
 
 #[test]