arm_compute::helpers::fft Namespace Reference

Functions
std::vector< unsigned int >	decompose_stages (unsigned int N, const std::set< unsigned int > &supported_factors)
	Decompose a given 1D input size using the provided supported factors. More...
std::vector< unsigned int >	digit_reverse_indices (unsigned int N, const std::vector< unsigned int > &fft_stages)
	Calculate digit reverse index vector given fft size and the decomposed stages. More...

Function Documentation

decompose_stages()

std::vector< unsigned int > decompose_stages	(	unsigned int	N,
		const std::set< unsigned int > &	supported_factors
	)

Decompose a given 1D input size using the provided supported factors.

Parameters

[in]	N	Input size to be decomposed.
[in]	supported_factors	Supported factors that can be used for decomposition.

Returns

A vector with the stages of the decomposition. Will be empty if decomposition failed.

Definition at line 34 of file fft.cpp.

References N.

Referenced by NEFFT1D::configure(), CLFFT1D::configure(), NEFFT1D::validate(), and CLFFT1D::validate().

{
    std::vector<unsigned int> stages;
    unsigned int              res = N;

    // Early exit if no supported factors are provided
    if(supported_factors.empty())
    {
        return stages;
    }

    // Create reverse iterator (Start decomposing from the larger supported factors)
    auto rfactor_it = supported_factors.rbegin();

    // Decomposition step
    while(res != 0)
    {
        const unsigned int factor = *rfactor_it;
        if(0 == (res % factor) && res >= factor)
        {
            stages.push_back(factor);
            res /= factor;
        }
        else
        {
            ++rfactor_it;
            if(rfactor_it == supported_factors.rend())
            {
                if(res > 1)
                {
                    // Couldn't decompose with given factors
                    stages.clear();
                    return stages;
                }
                else
                {
                    res = 0;
                }
            }
        }
    }

    return stages;
}

digit_reverse_indices()

std::vector< unsigned int > digit_reverse_indices	(	unsigned int	N,
		const std::vector< unsigned int > &	fft_stages
	)

Calculate digit reverse index vector given fft size and the decomposed stages.

Parameters

N	Input size to calculate digit reverse for
fft_stages	A vector with the FFT decomposed stages

Returns

A vector with the digit reverse indices. Will be empty if it failed.

Definition at line 79 of file fft.cpp.

References arm_compute::test::validation::reference::accumulate(), arm_compute::mlgo::parser::end(), arm_compute::test::validation::k, N, and arm_compute::test::validation::n.

Referenced by NEFFT1D::configure(), and CLFFT1D::configure().

{
    std::vector<unsigned int> idx_digit_reverse;

    // Early exit in case N and fft stages do not match
    const float stages_prod = std::accumulate(std::begin(fft_stages), std::end(fft_stages), 1, std::multiplies<unsigned int>());
    if(stages_prod != N)
    {
        return idx_digit_reverse;
    }

    // Resize digit reverse vector
    idx_digit_reverse.resize(N);

    // Get number of radix stages
    unsigned int n_stages = fft_stages.size();

    // Scan elements
    for(unsigned int n = 0; n < N; ++n)
    {
        unsigned int k  = n;
        unsigned int Nx = fft_stages[0];

        // Scan stages
        for(unsigned int s = 1; s < n_stages; ++s)
        {
            // radix of stage i-th
            unsigned int Ny = fft_stages[s];
            unsigned int Ni = Ny * Nx;

            // Update k index
            k = (k * Ny) % Ni + (k / Nx) % Ny + Ni * (k / Ni);

            // Update Nx
            Nx *= Ny;
        }

        // K is the index of digit-reverse
        idx_digit_reverse[n] = k;
    }

    return idx_digit_reverse;
}