std::aligned_alloc needs C++17: https://en.cppreference.com/w/cpp/memory/c/aligned_alloc

Whoops! I assume we can not mandate such function, can we?

OpenCV 4 requires >= C++11
I think OpenCV 5 requires >= C++17 ?

Looks like there are already plans to use std::aligned_alloc():

From a quick search, I did not find the minimal requirements (C++/C versions, target architectures, CUDA version/support, Python version/support, ...) for the different main OpenCV versions?

I think it would be great to add these info on these pages?

• https://docs.opencv.org/4.9.0/d1/dfb/intro.html
• https://github.com/opencv/opencv/wiki

@georgthegreat Thanks a lot for the contribution. The PR was discussed on OpenCV Core team meeting. We propose not to remove the existing branches, but wrap the new standard branch with C++ version guard and put it on the first priority. It means:

• No/less collisions in 4.x->5.x merge
• The standard branch is used first, if available

@asmorkalov, thanks for carrying out the negotiation.

I will bring the PR later on, but, first, what do you think about removing runtime checks for isAlignedAllocationEnabled()?

/cc @opencv-alalek @vpisarev

Both C11 and C++17 of aligned_alloc requires: "Passing a size which is not an integral multiple of alignment or an alignment which is not valid or not supported by the implementation causes the function to fail and return a null pointer (C11, as published, specified undefined behavior in this case, this was corrected by DR460)."

Proof:

• C++ 17: https://en.cppreference.com/w/cpp/memory/c/aligned_alloc
• C 11: https://en.cppreference.com/w/c/memory/aligned_alloc

Current OpenCV implementation does not follow the rule when the fastMalloc is called. It leads to the following test failures:

[ RUN      ] OCL_MeanStdDev_.ZeroMask
CV_MALLOC_ALIGN: 64
unknown file: Failure
C++ exception with description "OpenCV(4.12.0-dev) /mnt/Projects/Projects/opencv/modules/core/src/alloc.cpp:72: error: (-4:Insufficient memory) Failed to allocate 100 bytes in function 'OutOfMemoryError'
" thrown in the test body.
[  FAILED  ] OCL_MeanStdDev_.ZeroMask (3 ms)
[----------] 1 test from OCL_MeanStdDev_ (3 ms total)

[----------] 1 test from OCL_Gemm
[ RUN      ] OCL_Gemm.small
CV_MALLOC_ALIGN: 64
unknown file: Failure
C++ exception with description "OpenCV(4.12.0-dev) /mnt/Projects/Projects/opencv/modules/core/src/alloc.cpp:72: error: (-4:Insufficient memory) Failed to allocate 24 bytes in function 'OutOfMemoryError'
" thrown in the test body.
[  FAILED  ] OCL_Gemm.small (0 ms)