RM0020 datasheet(15/69 Pages) STMICROELECTRONICS

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RM0020

Function API

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Description:

Implements fast bit reversal permutation on 32-bit complex data using seed table as

described in David M.W.Evans, An Improved Digit-Reversal Permutation Algorithm for

the Fast Fourier and Hartley Transforms IEEE Transactions on Acoustics, Speech,

and Signal Processing, Vol. Assp-35, No. 8, August 1987.

Performance: See Section 7.

Example 2. bitrev_table_32bit

#include "libdsp2.h"

float inout_buffer[2*256];

void main() {

/* bit reverse permutation and calculation of 256-point FFT */

bitrev_table_32bit(16, inout_buffer, seed_radix2_32bit_256);

fft_quad_float(256, inout_buffer, w_table_radix2_float_256);

}

6.3

N-point radix-4 complex to complex float in-place FFT

Function call:

void fft_radix4_float(unsigned int N, float *inout_buffer,

float *twiddle_factor_table);

Arguments:

Description:

Computes the N-point radix-4 complex to complex float in-place fast Fourier transform

(FFT). Input 2-bit reversed data are stored in inout_buffer, output data are written over

the input data into inout_buffer. There is used radix-4 FFT algorithm.

Table 3.

fft_radix4_float arguments

Nin

FFT length, must be even power of two, tested for 64, 256,

1024, 4096

inout_buffer

in/out

pointer to the input/output vector of length 2*N, vector must be

double word aligned

memory layout:

x_Re(0) x_Im(0) x_Re(1) x_Im(1) ... x_Re(N-1) x_Im(N-1)

(Re - real part, Im - imaginary part)

twiddle_factor_table in

pointer to the vector of twiddle factors of length 3*N/2-4, vector

must be double word aligned

memory layout:

w_Re(0) w_Im(0) w_Re(1) w_Im(1) ... w_Re(3*N/4-3)

w_Im(3*N/4-3)

Use predefined w_table_radix4_float_N arrays.

The w_table_radix4_float_N is computed according to this

formula:

for k = 0, 1, ... 3*N/4-3

w_Re k

 iw_Im k



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