// Copy negative frequency components to end of buffer and zero out middle
//  inp    - input buffer of complex floats
//    n    - transform size
//  interp - interpolation amount
void zero_pad_freq(cfloat_t *inp, size_t n, size_t interp) {
    memmove(inp + n*interp - n/2, inp + (n+1)/2, (n+1)/2*sizeof(cfloat_t));
    memset (inp + n/2 + 1, 0,           (n*(interp-1)-1)*sizeof(cfloat_t));

    if (n % 2 == 0) {
        inp[n/2]          /= 2.0;
        inp[n*interp-n/2]  = conj(inp[n/2])/2.0;
    }
}