From d52b88b5257ea21a14ef7367d5e6557b8eb7efa0 Mon Sep 17 00:00:00 2001
From: carolcapps <carolcapps@protonmail.com>
Date: Sat, 13 Mar 2021 15:19:43 +0000
Subject: [PATCH] Fix increment of Uint256 with carry

---
 src/util/uint.rs | 55 ++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 51 insertions(+), 4 deletions(-)

diff --git a/src/util/uint.rs b/src/util/uint.rs
index 064ce121..c7a52265 100644
--- a/src/util/uint.rs
+++ b/src/util/uint.rs
@@ -516,13 +516,13 @@ impl Uint256 {
     #[inline]
     pub fn increment(&mut self) {
         let &mut Uint256(ref mut arr) = self;
-        arr[0] += 1;
+        arr[0] = arr[0].wrapping_add(1);
         if arr[0] == 0 {
-            arr[1] += 1;
+            arr[1] = arr[1].wrapping_add(1);
             if arr[1] == 0 {
-                arr[2] += 1;
+                arr[2] = arr[2].wrapping_add(1);
                 if arr[2] == 0 {
-                    arr[3] += 1;
+                    arr[3] = arr[3].wrapping_add(1);
                 }
             }
         }
@@ -689,6 +689,53 @@ mod tests {
                                       0x4AFCFF6F0375C608u64, 0x928D92B4D7F5DF33u64]));
     }
 
+    #[test]
+    pub fn increment_test() {
+        let mut val = Uint256([
+            0xFFFFFFFFFFFFFFFEu64,
+            0xFFFFFFFFFFFFFFFFu64,
+            0xFFFFFFFFFFFFFFFFu64,
+            0xEFFFFFFFFFFFFFFFu64,
+        ]);
+        val.increment();
+        assert_eq!(
+            val,
+            Uint256([
+                0xFFFFFFFFFFFFFFFFu64,
+                0xFFFFFFFFFFFFFFFFu64,
+                0xFFFFFFFFFFFFFFFFu64,
+                0xEFFFFFFFFFFFFFFFu64,
+            ])
+        );
+        val.increment();
+        assert_eq!(
+            val,
+            Uint256([
+                0x0000000000000000u64,
+                0x0000000000000000u64,
+                0x0000000000000000u64,
+                0xF000000000000000u64,
+            ])
+        );
+
+        let mut val = Uint256([
+            0xFFFFFFFFFFFFFFFFu64,
+            0xFFFFFFFFFFFFFFFFu64,
+            0xFFFFFFFFFFFFFFFFu64,
+            0xFFFFFFFFFFFFFFFFu64,
+        ]);
+        val.increment();
+        assert_eq!(
+            val,
+            Uint256([
+                0x0000000000000000u64,
+                0x0000000000000000u64,
+                0x0000000000000000u64,
+                0x0000000000000000u64,
+            ])
+        );
+    }
+
     #[test]
     pub fn uint256_bitslice_test() {
         let init = Uint256::from_u64(0xDEADBEEFDEADBEEF).unwrap();