/*

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 */

#include "dist_fft_twiddle.h"

// this function walks through data loading every fourth element

// the purpose is to cache the data for a subsequent FFT

dist_fft_real prefetch_row(dist_fft_storage data,

                           int local_row,

                           int dimension)

{

    // prefetching only speeds things up for very large dimensions

    if (dimension < (1 << 13)) return 0;

    int index = local_row * dimension;

    int index1 = index;

    int index2 = index+4;

    int index3 = index+8;

    int index4 = index+12;

    double data_re1;

    double data_im1;

    double data_re2;

    double data_im2;

    double data_re3;

    double data_im3;

    double data_re4;

    double data_im4;

    int bigloopcount;

    int bigloopindex;

    dist_fft_real sum_re1 = 0, sum_im1 = 0, sum_re2 = 0, sum_im2 = 0;

    dist_fft_real sum_re3 = 0, sum_im3 = 0, sum_re4 = 0, sum_im4 = 0;

    bigloopcount = (dimension)/16;

    for (bigloopindex=0; bigloopindex<bigloopcount; bigloopindex++) {

        data_re1 = c_re(data, index1);

        data_im1 = c_im(data, index1);

        data_re2 = c_re(data, index2);

        data_im2 = c_im(data, index2);

        data_re3 = c_re(data, index3);

        data_im3 = c_im(data, index3);

        data_re4 = c_re(data, index4);

        data_im4 = c_im(data, index4);

        sum_re1 += data_re1;

        sum_im1 += data_im1;

        sum_re2 += data_re2;

        sum_im2 += data_im2;

        sum_re3 += data_re3;

        sum_im3 += data_im3;

        sum_re4 += data_re4;

        sum_im4 += data_im4;

        index1 += 16;

        index2 += 16;

        index3 += 16;

        index4 += 16;

    }

    return sum_re1 * sum_im1 + sum_re2 * sum_im2 + sum_re3 * sum_im3 + sum_re4 * sum_im4;

}