Fix test_uint32_shr failing on debug builds. zcash#76

src/circuit/uint32.rs

@@ -175,7 +175,7 @@ impl UInt32 {
     }
 
     pub fn shr(&self, by: usize) -> Self {
-        let by = by % 32;
+        assert!(by < 32);
 
         let fill = Boolean::constant(false);
 
@@ -656,7 +656,7 @@ mod test {
         let mut rng = XorShiftRng::from_seed([0x5dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0654]);
 
         for _ in 0..50 {
-            for i in 0..60 {
+            for i in 0..32 {
                 let num = rng.gen();
                 let a = UInt32::constant(num).shr(i);
                 let b = UInt32::constant(num >> i);
@@ -671,6 +671,19 @@ mod test {
         }
     }
 
+    #[test]
+    fn test_uint32_shr_overflow() {
+        let mut rng = XorShiftRng::from_seed([0x5dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0654]);
+
+        for _ in 0..50 {
+            for i in 32..60 {
+                let num = rng.gen();
+                let result = std::panic::catch_unwind(|| UInt32::constant(num).shr(i));
+                assert!(result.is_err());
+            }
+        }
+    }
+
     #[test]
     fn test_uint32_sha256_maj() {
         let mut rng = XorShiftRng::from_seed([0x5dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0653]);