55#if !(defined(USE_FFTW) ^ defined(USE_KISS_FFT) ^ defined (USE_ACCELERATE_FFT))
56#error "You must define one FFT macro to ensure you select a FFT implementation - either USE_FFTW, USE_KISS_FFT or USE_ACCELERATE_FFT. You have either not defined one of these macros or you have defined more than one of them."