Merge pull request #28267 from akretz:absdiff-int

Fix absdiff with int arguments #28267

I believe the fix to the undefined behavior described in #27080 is simply casting to unsigned before subtraction, because

1. casting int to unsigned is well-defined; negative values get represented modulo $2^{32}$
2. overflow in unsigned subtraction is well-defined and the results are modulo $2^{32}$

Since we are computing everything modulo $2^{32}$ and the result must always be a non-negative number below $2^{32}$, this computation should be well-defined and correct.

I have verified this on ARM Apple Clang and on x64 Linux gcc with `-O3` and both produce the correct values in the reproducer of #27080. The test I have added fails with the integer overflow on both platforms I have tested. Perhaps @fengyuentau could verify if this also fixes the issue on the platforms he has tested?

I have added a fix and removed the workarounds. I recommended this approach in #28229, but he decided to revert it.


### 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
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/core/test/test_mat.cpp

@@ -2931,4 +2931,20 @@ TEST(Mat, copyAt_regression27298)
     }
 }
 
+TEST(Mat, issue_27080)
+{
+    const std::vector<int> src1 = {
+        605100952,281728648,-950765003,-270340785,-799079584,-1622966965,
+        -1717860046,-203390322,-1624721112,881300643,-1841646762,247438602,
+        -1871047900,2119496294,-868027786,1408019766,-2070408066,1782683247};
+    const std::vector<int> src2 = {
+        1746441532,892162071,-61301557,-1851870915,-1183525195,693709865,
+        1669181466,746688189,1883246439,-436799897,1428311842,-531665722,
+        1634935494,-1926207121,360363535,701351235,-1113337985,40823006};
+    const std::vector<int> src3 = {INT_MAX};
+    const std::vector<int> src4 = {INT_MIN};
+    EXPECT_EQ(cv::norm(src1, src2, NORM_L1), 32321818045.);
+    EXPECT_EQ(cv::norm(src3, src4, NORM_L1), UINT_MAX);
+}
+
 }} // namespace