dsps_cplx2real_fc32 cannot be used without fft4r initialization (DSP-73)

[KaSroka]

In my application I'm using radix-2 FFT (I'm using 4096 real points so FFT is 2048 points). Current implementation of dsps_cplx2real_fc32 requires fft radix-4 to be initialized to work properly.

Why there is no implementation for radix-2 alone? Having to init radix-4 wastes 32kB of RAM in my application for tables that are only needed for dsps_cplx2real_fc32.

[dmitry1945]

Hi @KaSroka , it should be possible. I will check. Will update if found something.

Regards, Dmitry

[KaSroka]

dsps_cplx2real_fc32 is defined as dsps_cplx2real_fc32_ae32 when using CONFIG_DSP_OPTIMIZED. dsps_cplx2real_fc32_ae32 is defined as a call to dsps_cplx2real_fc32_ae32_ with dsps_fft4r_w_table_fc32 as table and dsps_fft4r_w_table_size as table_size. These is no version that uses radix-2 tables. When explicitly calling dsps_cplx2real_fc32_ae32_ with dsps_fft_w_table_fc32 as table and dsps_fft_w_table_size as table_size the algorithm doesn't work as it expects radix-4 table which is bigger. There is no definition of dsps_cplx2real_fc32 in dsps_fft2r_fc32* files, there is only dsps_cplx2reC_fc32 but it's for other scenarios. Also ANSI version of dsps_cplx2real_fc32 checks if radix-4 FFT is initialized.

[KaSroka]

Also the docstring for dsps_cplx2real_fc32_ae32_ is wrong as it mentions two inputs and this is responsibility of dsps_cplx2reC_fc32

[dmitry1945]

Hi @KaSroka

Yes, the dsps_cplx2real_fc32(...) can be used only if FFT4R was initialized because this function use FFT4R tables. I have add the description about this, and release will be soon. If you use this function you have to initialize FFT4R, because the allocated size of memory will be almost the same, and FFT4R is ~30 % faster then FFT2R. If the time is very critical, better to use FFT4R. To have FFT2R with real input it's better to use dsps_cplx2reC_fc32 and two real inputs at the same time.

Thanks, Dmitry