static SwsVector *sws_getShiftedVec(SwsVector *a, int shift)
{
    int length= a->length + FFABS(shift)*2;
    int i;
    SwsVector *vec= sws_getConstVec(0.0, length);

    if (!vec)
        return NULL;

    for (i=0; i<a->length; i++) {
        vec->coeff[i + (length-1)/2 - (a->length-1)/2 - shift]= a->coeff[i];
    }

    return vec;
}