Class TwiddleTable

src/library/generator.stockham.cpp:524–602

Twiddle factors table

	// Twiddle factors table
    class TwiddleTable
    {
        size_t N; // length
		double *wc, *ws; // cosine, sine arrays

	public:
		TwiddleTable(size_t length) : N(length)
		{
			// Allocate memory for the tables
			// We compute twiddle factors in double precision for both P_SINGLE and P_DOUBLE
			wc = new double[N];
			ws = new double[N];
		}

		~TwiddleTable()
		{
			// Free
			delete[] wc;
			delete[] ws;
		}

		template <Precision PR>
		void GenerateTwiddleTable(const std::vector<size_t> &radices, std::string &twStr)
		{
			const double TWO_PI = -6.283185307179586476925286766559;

			// Make sure the radices vector sums up to N
			size_t sz = 1;
			for(std::vector<size_t>::const_iterator i = radices.begin();
				i != radices.end(); i++)
			{
				sz *= (*i);
			}
			assert(sz == N);

			// Generate the table
			size_t L = 1;
			size_t nt = 0;
			for(std::vector<size_t>::const_iterator i = radices.begin();
				i != radices.end(); i++)
			{
				size_t radix = *i;

				L *= radix;

				// Twiddle factors
				for(size_t k=0; k<(L/radix); k++)
				{
					double theta = TWO_PI * ((double)k)/((double)L);

					for(size_t j=1; j<radix; j++)
					{
						double c = cos(((double)j) * theta);
						double s = sin(((double)j) * theta);

						//if (fabs(c) < 1.0E-12)	c = 0.0;
						//if (fabs(s) < 1.0E-12)	s = 0.0;