"TMS320C55x DSP Library DSPLIB Programmer's Reference"

cifftcifftFunctionInverse Complex FFTvoid cifft (DATA *x, ushort nx, type);(defined in cifft.asm)Argumentsx [2*nx]nxtypePointer to input vector containing nx complex elements(2*nx real elements) in bit-reversed order. On output, vectora contains the nx complex elements of the IFFT(x).Complex numbers are stored in interleaved Re-Im format.Number of complex elements in vector x. Must be between8 and 1024.FFT type selector. Types supported: If type = SCALE, scaled version selected If type = NOSCALE, non-scaled version selectedDescriptionAlgorithmComputes a complex nx-point IFFT on vector x, which is in bit-reversed order.The original content of vector x is destroyed in the process. The nx complexelements of the result are stored in vector x in normal-order.(IDFT)y[k] 1nx1(scale factor) * x[w]*cos 2* nx* i * k j sin 2* nx* i * ki0Overflow Handling MethodologyIf scale==1, scaling before each stage is implemented for overflowpreventionSpecial RequirementsThis function requires the inclusion of file “twiddle.inc” which contains thetwiddle table (automatically included).Data memory alignment (reference cfft.cmd in examples/cifft directory):Alignment of input database address: (n+1) LSBs must be zeros,where n = log 2 (nx).Ensure that the entire array fits within a 64K boundary (the largest possiblearray addressable by the 16-bit auxiliary register).For best performance the data buffer has to be in a DARAM block.If the twiddle table and the data buffer are in the same block then theradix-2 kernal is 7 cycles and the radix-4 kernel is not affected.Function Descriptions4-21