• OpenCV => 4.3
• Operating System / Platform =>Mac OS Catalina + OpenCL + IPP
• Compiler => clang

Detailed description

countNonZero is returning wrong counts for large unit8_t arrays.

The issue seems to be related to ippiCountInRange_8u_C1R which is called behind the scene returning a wrong inverse count.

Steps to reproduce

std::cout << cv::countNonZero(cv::Mat::zeros(1,524190-1,CV_8UC1));     // returns 0
std::cout << cv::countNonZero(cv::Mat::zeros(1,524190,CV_8UC1));        // returns 65536
std::cout << cv::countNonZero(cv::Mat::zeros(1,524190+1,CV_8UC1));    // returns 65536