"TMS320C55x DSP Library DSPLIB Programmer's Reference"

ifftrifftFunctionInverse Real FFT (in-place)void rifft (DATA *x, ushort nx, type);(reference cifft.asm)Argumentsx [nx]nxtypePointer to input vector x containing nx real elements. Theunpacki routine should be called to unpack the rfft sequencebefore calling the bit reversal routine. (See examples directoryfor calling sequence)On output, the vector x contains nx complex elementscorresponding to RIFFT(x) or the signal itself.Number of real elements in vector x. nx can take the followingvalues.nx =16, 32, 64, 128, 256, 512, 1024RFFT type selector. Types supported: If type = SCALE, scaled version selected If type = NOSCALE, non-scaled version selectedDescriptionAlgorithmComputes a Radix-2 real DIT IFFT of the nx real elements stored in vector xin bit-reversed order. The original content of vector x is destroyed in theprocess. The first nx/2 complex elements of the IFFT(x) are stored in vectorx in normal-order.(IDFT)See CIFFTSpecial RequirementsThis function should work with unpacki.asm and/or cbrev.asm for properresult. See example in examples/rifft directory.Memory alignment: input data (x) must be aligned at even word boundary.Data memory alignment (referenced rfft.cmd in examples/rfft 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 kernel is 7 cycles and the radix-4 kernel is not affected.Function Descriptions4-87