int WebRtcSpl_RealInverseFFT(struct RealFFT* self,
const int16_t* complex_data_in,
int16_t* real_data_out) {
int i = 0;
int j = 0;
int result = 0;
int n = 1 << self->order;
// Create the buffer specific to complex-valued FFT implementation.
int16_t complex_buffer[2 << kMaxFFTOrder];
// For n-point FFT, first copy the first n + 2 elements into complex
// FFT, then construct the remaining n - 2 elements by real FFT's
// conjugate-symmetric properties.
memcpy(complex_buffer, complex_data_in, sizeof(int16_t) * (n + 2));
for (i = n + 2; i < 2 * n; i += 2) {
complex_buffer[i] = complex_data_in[2 * n - i];
complex_buffer[i + 1] = -complex_data_in[2 * n - i + 1];
}
WebRtcSpl_ComplexBitReverse(complex_buffer, self->order);
result = WebRtcSpl_ComplexIFFT(complex_buffer, self->order, 1);
// Strip out the imaginary parts of the complex inverse FFT output.
for (i = 0, j = 0; i < n; i += 1, j += 2) {
real_data_out[i] = complex_buffer[j];
}
return result;
}
int WebRtcSpl_RealInverseFFTC(struct RealFFT* self,
const int16_t* data_in,
int16_t* data_out) {
memcpy(data_out, data_in, sizeof(int16_t) * (1 << (self->order + 1)));
WebRtcSpl_ComplexBitReverse(data_out, self->order);
return WebRtcSpl_ComplexIFFT(data_out, self->order, 1);
}
