corr.c

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/* corr.c - sample cross correlation of two length-N signals */
 
#include "tools.h"
 
void corr(int N, float x[N], float y[N], int M, float R[M])                  /* computes \‍(R[k]\‍), \‍(k = 0, 1,\dotsc, M\‍) */
                        /* \‍(x,y\‍) are \‍(N\‍)-dimensional */
                        /* \‍(R\‍) is \‍((M+1)\‍)-dimensional */
{
       int k, n;
 
       for (k=0; k<M; k++)
              for (R[k]=0, n=0; n<N-k; n++)
                     R[k] += x[n+k] * y[n] / N;
}
 
#include <stdlib.h>
#include <stdio.h>
#include "tools.h"
int main(int argc, char **argv) {
        int n = atoi(argv[1]);
        int k = 5;
        //int k = atoi(argv[3]);
        float (*in)[n] = (float (*)[n])malloc(sizeof(float)*(1+n));
        float (*in2)[n] = (float (*)[n])malloc(sizeof(float)*(1+n));
        float (*out)[k] = (float (*)[n])malloc(sizeof(float)*(k));
        init_args(argc, argv);
        init_data_float(*in,n);
        init_data_float(*in2,n);
 
        if (argc>20) k=10;
        struct timeval s,e;
        gettimeofday(&s,NULL);
        corr(n,*in,*in2,k,*out);
        gettimeofday(&e,NULL);
        double diff = (double)(e.tv_sec-s.tv_sec)*1000.0 +
                (double)(e.tv_usec-s.tv_usec)/1000.0;
        printf("%0.6f\n", diff);
        return 0;
}