Fastest way to fill complex matrix with incoming data. Armadillo Library

Question

I have situation where each 1ms is coming new buffer of 2*200 samples of int16_t. (multiplied by 2 is because complex data)

Those data should be added into Armadillo Complex Double Matrix, in the fastest way possible (less than 1 ms), to specific slot.

Does anyone know better approach?

Current test code takes longer than 1ms (tested with both cases)

nb_of_samples = 200;


    void write(uint32_t rawId, uint32_t slotId, int16_t *samples) 
    {
        size_t currentBlock = slotId * nb_of_samples; // slot identification 
        auto const memPtr = matrix.colptr(currentBlock) + rawId; // pointer to position from where to start write new received samples
        std::for_each(std::execution::par_unseq, m_index.begin(), m_index.end(), [&memPtr, &samples](size_t index)
        {
            new (memPtr + index) std::complex<double>(samples[index], samples[index+1]);
        });
//        second idea, simple for 
//        for(size_t i = 0; i < NB_OF_SAMPLES; ++i)
//        {
//            new (memPtr + i) std::complex<double>(samples[i], samples[i+1]);
//        }
    }

Answer 1

C++ makes a special exception to aliasing and UB rules for std::complex . This is done for compatibility of widely used C subroutines.

https://en.cppreference.com/w/cpp/numeric/complex

So you can just use something simple like this:

void convert(std::complex<double> *pout, const uint16_t* pin)
{
    for (size_t i = 0; i < nb_of_samples*2 ; i++)
        reinterpret_cast<double*>(pout)[i] = pin[i];
}