Texas Instruments TMS320C64X manual DSPfft16x32

DSP_fft16x32

DSP_fft16x32	Complex Forward Mixed Radix 16 x 32-bit FFT With Rounding
Function
		void DSP_fft16x32(const short * restrict w, int nx, int * restrict x, int * restrict y)
Arguments		w[2*nx]	Pointer to complex Q.15 FFT coefficients.
		nx	Length of FFT in complex samples. Must be power of 2 or 4,
			and 16 ≤ nx ≤ 32768.
		x[2*nx]	Pointer to complex 32-bit data input.
		y[2*nx]	Pointer to complex 32-bit data output.
Description		This routine computes an extended precision complex forward mixed radix
		FFT with rounding and digit reversal. Input data x[ ] and output data y[ ] are
		32-bit, coefficients w[ ] are 16-bit. The output is returned in the separate array
		y[ ] in normal order. Each complex value is stored with interleaved real and
		imaginary parts. The code uses a special ordering of FFT coefficients (also
		called twiddle factors) and memory accesses to improve performance in the
		presence of cache. The C code to generate the twiddle factors is the same as
		the one used for the DSP_fft16x16r routine.
Algorithm		The C equivalent of the assembly code without restrictions is similar to the one
		shown for the DSP_fft16x16t routine. For further details, see the source code
		of the C version of this function, which is provided with this library. Note that
		the assembly code is hand optimized and restrictions may apply.

Special Requirements

-In-place computation is not allowed.

-The size of the FFT, nx, must be a power of 4 or 2 and greater than or equal to 16 and less than 32768.

-The arrays for the complex input data x[ ], complex output data y[ ], and twiddle factors w[ ] must be double-word aligned.

-The input and output data are complex, with the real/imaginary components stored in adjacent locations in the array. The real components are stored at even array indices, and the imaginary components are stored at odd array indices.

-The FFT coefficients (twiddle factors) are generated using the program tw_fft16x32 provided in the directory ‘support\fft’. The scale factor must be 32767.5. No scaling is done with the function; thus, the input data must be scaled by 2log2(nx) to completely prevent overflow.

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