From 196a8afe764ad8658cb2027fa0f808a64be41fff Mon Sep 17 00:00:00 2001 From: Adrian Kretz Date: Sun, 15 Feb 2026 08:29:29 +0100 Subject: [PATCH] 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/include/opencv2/core/base.hpp | 2 +- modules/core/src/norm.simd.hpp | 47 ---------------------- modules/core/test/test_mat.cpp | 16 ++++++++ 3 files changed, 17 insertions(+), 48 deletions(-) diff --git a/modules/core/include/opencv2/core/base.hpp b/modules/core/include/opencv2/core/base.hpp index 4975f9df97..b9cb9a3f30 100644 --- a/modules/core/include/opencv2/core/base.hpp +++ b/modules/core/include/opencv2/core/base.hpp @@ -316,7 +316,7 @@ inline int cv_absdiff(uchar x, uchar y) { return (int)std::abs((int)x - (int)y); inline int cv_absdiff(schar x, schar y) { return (int)std::abs((int)x - (int)y); } inline int cv_absdiff(ushort x, ushort y) { return (int)std::abs((int)x - (int)y); } inline int cv_absdiff(short x, short y) { return (int)std::abs((int)x - (int)y); } -inline unsigned cv_absdiff(int x, int y) { return (unsigned)(std::max(x, y) - std::min(x, y)); } +inline unsigned cv_absdiff(int x, int y) { return (unsigned)std::max(x, y) - (unsigned)std::min(x, y); } inline unsigned cv_absdiff(unsigned x, unsigned y) { return std::max(x, y) - std::min(x, y); } inline uint64 cv_absdiff(uint64 x, uint64 y) { return std::max(x, y) - std::min(x, y); } inline float cv_absdiff(hfloat x, hfloat y) { return std::abs((float)x - (float)y); } diff --git a/modules/core/src/norm.simd.hpp b/modules/core/src/norm.simd.hpp index cc82e403ca..05c6dde0ed 100644 --- a/modules/core/src/norm.simd.hpp +++ b/modules/core/src/norm.simd.hpp @@ -77,32 +77,6 @@ struct NormDiffL1_SIMD { } }; -// This specialization is needed because https://github.com/opencv/opencv/issues/27080 -template <> -struct NormDiffL1_SIMD { - inline double operator() (const int* src1, const int* src2, int n) const { - double s = 0; - int j = 0; -#if (CV_SIMD_64F || CV_SIMD_SCALABLE_64F) - v_float64 r0 = vx_setzero_f64(), r1 = vx_setzero_f64(); - for (; j <= n - VTraits::vlanes(); j += VTraits::vlanes()) { - v_int32 v01 = vx_load(src1 + j), v02 = vx_load(src2 + j); - v_uint32 v0 = v_absdiff(v01, v02); - v_uint64 ev0, ev1; - v_expand(v0, ev0, ev1); - r0 = v_add(r0, v_cvt_f64(v_reinterpret_as_s64(ev0))); - r1 = v_add(r1, v_cvt_f64(v_reinterpret_as_s64(ev1))); - } - s += v_reduce_sum(v_add(r0, r1)); -#endif - for (; j < n; j++) { - double d1 = (double)src1[j], d2 = (double)src2[j]; - s += (double)std::abs(d1 - d2); - } - return s; - } -}; - template struct NormDiffL2_SIMD { inline ST operator() (const T* src1, const T* src2, int n) const { @@ -1348,27 +1322,6 @@ normDiffL1_(const T* src1, const T* src2, const uchar* mask, ST* _result, int le return 0; } -// This specialization is needed because https://github.com/opencv/opencv/issues/27080 -template<> int -normDiffL1_(const int* src1, const int* src2, const uchar* mask, double* _result, int len, int cn) { - double result = *_result; - if( !mask ) { - NormDiffL1_SIMD op; - result += op(src1, src2, len*cn); - } else { - for( int i = 0; i < len; i++, src1 += cn, src2 += cn ) { - if( mask[i] ) { - for( int k = 0; k < cn; k++ ) { - double d1 = (double)src1[k], d2 = (double)src2[k]; - result += (double)std::abs(d1 - d2); - } - } - } - } - *_result = result; - return 0; -} - template int normDiffL2_(const T* src1, const T* src2, const uchar* mask, ST* _result, int len, int cn) { ST result = *_result; diff --git a/modules/core/test/test_mat.cpp b/modules/core/test/test_mat.cpp index 07dc859cf1..b57559c2b1 100644 --- a/modules/core/test/test_mat.cpp +++ b/modules/core/test/test_mat.cpp @@ -2931,4 +2931,20 @@ TEST(Mat, copyAt_regression27298) } } +TEST(Mat, issue_27080) +{ + const std::vector src1 = { + 605100952,281728648,-950765003,-270340785,-799079584,-1622966965, + -1717860046,-203390322,-1624721112,881300643,-1841646762,247438602, + -1871047900,2119496294,-868027786,1408019766,-2070408066,1782683247}; + const std::vector src2 = { + 1746441532,892162071,-61301557,-1851870915,-1183525195,693709865, + 1669181466,746688189,1883246439,-436799897,1428311842,-531665722, + 1634935494,-1926207121,360363535,701351235,-1113337985,40823006}; + const std::vector src3 = {INT_MAX}; + const std::vector src4 = {INT_MIN}; + EXPECT_EQ(cv::norm(src1, src2, NORM_L1), 32321818045.); + EXPECT_EQ(cv::norm(src3, src4, NORM_L1), UINT_MAX); +} + }} // namespace