RM0020 datasheet(22/69 Pages) STMICROELECTRONICS

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Function API

RM0020

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Description:

Computes the last stage of N-point radix-2 complex to complex frac32 in-place fast

Fourier transform (FFT). Input data are stored in inout_buffer, output data are written

over the input data into inout_buffer. This function is used to calculate the FFT for

lengths which are odd power of two (128, 512, 2048).

Note: There must be at least 16 bytes of readable memory behind inout_buffer.

Performance: See Section 7 and Table 37.

Example 8. fft_radix2_last_stage_frac32

#include "libdsp2.h"

int inout_buffer[2*512];

void main() {

/* bit reverse permutation and calculation of 512-point FFT */

bitrev_table_16bit(16, (short *)(inout_buffer+512),

seed_radix2_16bit_512);

fft_quad_frac32(512, inout_buffer, w_table_radix2_frac32_512);

fft_radix2_last_stage_frac32(512, inout_buffer,

w_table_radix2_frac32_512);

}

6.9

Split function of N-point real to complex float FFT

Function call:

void fft_real_split_float(unsigned int N, float *y, float *wa,

float *wb);

twiddle_factor_table in

pointer to the vector of twiddle factors of length N, vector must

be double word aligned

memory layout:

w_Re(0) w_Im(0) w_Re(1) w_Im(1) ... w_Re(N/2-1) w_Im(N/2-1)

Use predefined w_table_radix2_frac32_N arrays.

The w_table_radix2_frac32_N is computed according to this

formula:

for k = 0, 1, ... N/2-1

Table 8.

fft_radix2_last_stage_frac32 arguments (continued)

w_Re k

 iw_Im k





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