Question about gr_fft_filter_ccc.cc

Hi,
I found ofdm receiver will go through the file
gr_fft_filter_ccc.cc.
Anyone can explain what does this file do? What is d_xformed_taps?

Thanks,
Bin

BTW, I believe “gr_fft_vcc_fftw.cc” is where the IFFT and FFT happens
for
transmitter and receiver.