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DSP_fft16x16
4-8
4.3 FFT
Complex Forward Mixed Radix 16 x 16-bit FFT
DSP_fft16x16
Function void DSP_fft16x16(const short * restrict w, int nx, short * restrict x, short *
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 16-bit data input.
y[2*nx] Pointer to complex 16-bit data output.
Description This routine computes a complex forward mixed radix FFT with rounding and
digit reversal. Input data x[ ], output data y[ ], and 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.
Algorithm All stages are radix-4 except the last one, which can be radix-2 or radix-4,
depending on the size of the FFT. All stages except the last one scale by two
the stage output data.
Special Requirements
- In-place computation is not allowed.
- The size of the FFT, nx, must be power of 2 or 4, and 16 ≤ nx ≤ 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. All data are in short precision
or Q.15 format.