From 88f2f459db381e865ef2df78aa5123adcf32110e Mon Sep 17 00:00:00 2001
From: perry_lin <2628192835@qq.com>
Date: Sun, 30 Aug 2026 17:04:25 +0800
Subject: [PATCH] Merge pull request #29069 from
 perrylin4:fix/11988-rect-unsigned-intersection

core: fix unsigned Rect intersection for disjoint rectangles (#11988) - #29069

Fixes #11988

## Problem
`Rect_<_Tp>::operator&` / `operator&=` returned a non-empty rectangle when two **unsigned** rectangles do not overlap.

### Example:
```cpp
cv::Rect_<unsigned> r1(0, 0, 1, 1);
cv::Rect_<unsigned> r2(2, 2, 1, 1);
auto inter = r1 & r2;  // was [1 x 1 from (2, 2)], expected empty
```
Root cause: the previous implementation subtracted edge coordinates before checking overlap. For `unsigned _Tp`, expressions like `width - (x_max - x_min)` can underflow when rectangles are disjoint.

### Solution
Add a check for underflow

### Tests
Added regression test `Core_Rect.test_unsigned_overflow in modules/core/test/test_misc.cpp`.
---
 modules/core/include/opencv2/core/types.hpp |  9 +++++++++
 modules/core/test/test_misc.cpp             | 11 +++++++++++
 2 files changed, 20 insertions(+)

diff --git a/modules/core/include/opencv2/core/types.hpp b/modules/core/include/opencv2/core/types.hpp
index 1f54d9563d..1c962dcae4 100644
--- a/modules/core/include/opencv2/core/types.hpp
+++ b/modules/core/include/opencv2/core/types.hpp
@@ -2012,6 +2012,15 @@ Rect_<_Tp>& operator &= ( Rect_<_Tp>& a, const Rect_<_Tp>& b )
         a = Rect_<_Tp>();
         return a;
     }
+
+    // If the delta between x/y coordinates exceeds the corresponding width/height,
+    // the rectangles cannot overlap and `width - delta` would underflow for unsigned types.
+    if (Rx_min.width < (Rx_max.x - Rx_min.x) ||
+        Ry_min.height < (Ry_max.y - Ry_min.y)) {
+        a = Rect_<_Tp>();
+        return a;
+    }
+
     // We now know that either Rx_min.x >= 0, or
     // Rx_min.x < 0 && Rx_min.x + Rx_min.width >= Rx_max.x and therefore
     // Rx_min.width >= (Rx_max.x - Rx_min.x) which means (Rx_max.x - Rx_min.x)
diff --git a/modules/core/test/test_misc.cpp b/modules/core/test/test_misc.cpp
index 94b4d83781..1682ff27ea 100644
--- a/modules/core/test/test_misc.cpp
+++ b/modules/core/test/test_misc.cpp
@@ -996,6 +996,17 @@ REGISTER_TYPED_TEST_CASE_P(Rect_Test, Overflows, OnTheEdge);
 typedef ::testing::Types<int, float, double> RectTypes;
 INSTANTIATE_TYPED_TEST_CASE_P(Negative_Test, Rect_Test, RectTypes);
 
+TEST(Core_Rect, test_unsigned_overflow_11988)
+{
+    typedef Rect_<unsigned> R;
+    R r1(0, 0, 1u, 1u);
+    R r2(2u, 2u, 1u, 1u);
+    auto inter = r1 & r2;
+    EXPECT_EQ(R(), inter);
+    EXPECT_EQ(0u, inter.area());
+    EXPECT_TRUE(inter.empty());
+}
+
 // Expected that SkipTestException thrown in the constructor should skip test but not fail
 struct TestFixtureSkip: public ::testing::Test {
     TestFixtureSkip(bool throwEx = true) {