"TMS320C55x DSP Library DSPLIB Programmer's Reference"

fftThe initial estimate can be obtained from a look-up table, from choosing a midpoint,or simply from linear interpolation. The method chosen for this problemis linear interpolation and is accomplished by taking the complement of theleast significant bits of the Xnorm value.Overflow Handling MethodologynoneSpecial Requirements noneImplementation Notes noneExampleBenchmarksSee examples/recip16 subdirectory(preliminary)Cycles † Core: 33 * nxOverhead: 12Code size(in bytes)69† Assumes all data is in on-chip dual-access RAM and that there is no bus conflict due to twiddletable reads and instruction fetches (provided linker command file reflects those conditions).rfftFunctionForward Real FFT (in-place)void rfft (DATA *x, ushort nx, type);(reference cfft.asm and unpack.asm)Argumentsx [nx]nxPointer to input vector containing nx real elements. On output,vector x contains the first half (nx/2 complex elements) of theFFT output in the following order. Real FFT is a symmetricfunction around the Nyquist point, and for this reason only halfof the FFT(x) elements are required.On output x will contain the FFT(x) = y in the following format:y(0)Re y(nx/2)im → DC and Nyquisty(1)Re y(1)Imy(2)Re y(2)Im....y(nx/2)Re y(nx/2)ImComplex numbers are stored in Re-Im formatNumber of real elements in vector x. can take the followingvalues.nx = 16, 32, 64, 128, 256, 512, 1024Function Descriptions4-85