From 2d781f51e1fe5e9c7f465d774098fe57796b54a3 Mon Sep 17 00:00:00 2001
From: Sridhar <paidipellysridhar2005@gmail.com>
Date: Wed, 9 Sep 2026 14:45:52 +0530
Subject: [PATCH] Merge pull request #29878 from
 sridhar-git05:fix-broadcast-zero-dimension
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

core: handle zero-sized broadcast dimensions #29878

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

<!-- Note!!! If you are an automated agent, we have a special process for you: add 🤖🤖🤖 to the end of the PR title. -->

### Changes

- Added test coverage for the zero-sized dimension case in `cv::broadcast()`.
- The test exercises the `false` branch of `_flatten_for_broadcast()`.
- Fixed division by zero when the broadcast destination has zero elements.

### Test

- `opencv_test_core.exe --gtest_filter=BroadcastTo.*`

All `BroadcastTo` tests pass.

Fixes #28910
---
 modules/core/src/matrix_transform.cpp |  2 ++
 modules/core/test/test_arithm.cpp     | 17 +++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/modules/core/src/matrix_transform.cpp b/modules/core/src/matrix_transform.cpp
index fd9485d271..309d8d7ec2 100644
--- a/modules/core/src/matrix_transform.cpp
+++ b/modules/core/src/matrix_transform.cpp
@@ -1335,6 +1335,8 @@ void broadcast(InputArray _src, InputArray _shape, OutputArray _dst) {
             #undef OPENCV_CORE_BROADCAST_LOOP
         }
     } else {
+        if (dst.total() == 0)
+            return;
         // initial copy (src to dst)
         std::vector<size_t> step_src{src.step.p, src.step.p + dims_src};
         if (step_src.size() < static_cast<size_t>(dims_shape)) {
diff --git a/modules/core/test/test_arithm.cpp b/modules/core/test/test_arithm.cpp
index 7eb642b51d..ffe6ead18e 100644
--- a/modules/core/test/test_arithm.cpp
+++ b/modules/core/test/test_arithm.cpp
@@ -2628,6 +2628,23 @@ TEST(BroadcastTo, basic) {
         broadcast(_src, shape, dst);
         fn_verify(ref, dst);
     }
+
+    {
+        std::vector<int> shape{1, 0};
+        std::vector<int> data;
+        Mat zero_src(static_cast<int>(shape.size()), shape.data(), CV_32FC1, data.data());
+
+        std::vector<int> target_shape{3, 0};
+        Mat dst;
+
+        broadcast(zero_src, target_shape, dst);
+
+        EXPECT_EQ(dst.dims, 2);
+        EXPECT_EQ(dst.size[0], 3);
+        EXPECT_EQ(dst.size[1], 0);
+        EXPECT_EQ(dst.total(), 0u);
+    }
+
 }
 
 TEST(Core_minMaxIdx, regression_9207_2)