naive.c

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#include "s2kit/naive.h"
 
#include <math.h>
#include <string.h>
 
void DLTNaive(double* data, const int bw, const int m, double* weights, double* result, double* pml_table,
              double* workspace) {
    int size = 2 * bw;
 
    /*
        Apply quadrature weights.
 
        We only have to differentiate between even and odd weights when doing something like seminaive,
        something which involves the dct. In this naive case, the parity of the order of the transform
        doesn't matter because we are not dividing by sin(x) when precomputing the Legendres
        (because we are not taking their dct). The plain weights are just fine.
    */
    double* weighted_data = workspace;
    for (int i = 0; i < size; ++i)
        weighted_data[i] = data[i] * weights[i];
 
    for (int i = 0; i < bw - m; ++i) {
        double sum = 0.;
        for (int j = 0; j < size; ++j)
            sum += weighted_data[j] * pml_table[j];
 
        result[i] = sum;
 
        pml_table += size;
    }
}
 
void InvDLTNaive(double* coeffs, const int bw, const int m, double* result, double* pml_table) {
    int size = 2 * bw;
 
    memset(result, 0, sizeof(double) * size); // make sure result is zeroed out
 
    for (int i = 0; i < bw - m; ++i) {
        double coeff = coeffs[i];
 
        if (coeff == 0.) {
            pml_table += size;
            continue;
        }
 
        for (int j = 0; j < size; ++j)
            result[j] += coeff * pml_table[j];
 
        pml_table += size;
    }
}