The DSPF_sp_fftSPxSP function in DSPlib is the complex single precision floating point implementation available in DSP lib. This uses the complex_mpysp instrinsics. The assembly implementation of this function is available which using the cmpysp and daddsp instructions. The twiddle factors and the complex input are given in the function such that the real and imaginary results are generated appropriately. The complex_mpysp intrinsics uses the cmpysp followed by daddsp instructions which are described in the user guide. Please refer the description of these instructions.
http://www.ti.com/lit/ug/sprugh7/sprugh7.pdf
CMPYSP instruction performs a complex multiply of two Single Precision Floating-Point numbers in a register pair giving a 128-bit output. The details from the document is below.
The product of the lower word of src1 and the upper word of src2 to is placed into dst_0.
The product of the lower word of src1 and the lower word of src2 is negated and placed into dst_1.
The product of the upper word of src1 and the lower word of src2 to is placed into dst_2.
The product of the upper word of src1 and the upper word of src2 to is placed into dst_3.
The test bench of the SP complex floating point FFT function is provided with the DSPlib function. The output of the C, optimized C and assembly implementation matches in the test bench.
Regards
Asheesh