ac[0] += 10;
void _spx_autocorr(const float *x,   /*  in: [0...n-1] samples x   */float       *ac,  /* out: [0...lag-1] ac values */int          lag, int          n){   float d;   int i;   while (lag--)    {      for (i = lag, d = 0; i < n; i++)          d += x[i] * x[i-lag];      ac[lag] = d;   }}