parallel memory 303 is 2 b when the parallel granularity is 2 b accordingly twiddle factors for the respective computation stages 404 of the butterfly group 402 may be calculated in advance and stored sequentially in one of the memory rows of the multi granularity parallel memory 303 the twiddle factors for the butterfly group may be read in parallel with a granularity of 2 b during the computation fig7 shows how the twiddle factors for the respective computation stages 404 of the butterfly group 402 are stored in the memory row 700 when the parallel granularity is 8 701 denotes a twiddle factor for the 1 st computation stage 702 denotes two twiddle factors for the 2 nd computation stage and 703 denotes four twiddle factors for the 3 rd computation stage step 3 reading data required for fft butterfly computation stored in the jth memory row 805 of the ith memory block 804 in the multi granularity parallel memory 300 or 302 with a read granularity of 2 b where i and j each have an initial value of 0 and reading sequentially from the multi granularity parallel memory 303 the twiddle factors required for fft butterfly computation with a granularity of 2 b in the order of the memory rows when reading data for butterfly computation the read granularity is set as 2 b and data for fft butterfly computation stored in the respective memory rows 805 of the memory blocks 804 in the multi granularity parallel memory 300 are read sequentially that is the read operation starts with the zeroth memory row 805 of the zeroth memory block 804 then the first memory row 805 of the zeroth memory block 804 and so on until all the memory rows 805.