RM0020 datasheet(20/69 Pages) STMICROELECTRONICS

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Function API

RM0020

20/69

By default it is turned on. The scaling is performed by dividing by 4 before each pair of

radix-2 stages.

Algorithm:

Equation 7

for each n from 0 to N-1, scaled down by N if scaling is turned on

Equation 8

where i is the imaginary unit with the property that:

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

Performance: See Section 7 and Table 36.

Example 6. fft_quad_frac32

#include "libdsp2.h"

int inout_buffer[2*256];

void main() {

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

bitrev_table_16bit(16, (short *)(inout_buffer+256),

seed_radix2_16bit_256);

fft_quad_frac32(256, inout_buffer, w_table_radix2_frac32_256);

}

6.7

Last stage of N-point radix-2 complex to complex float in-

place FFT

Function call:

void fft_radix2_last_stage_float(unsigned int N, float

*inout_buffer,

float *twiddle_factor_table);

Arguments:



 w



–



i

--------

–

Table 7.

fft_radix2_last_stage_float arguments

FFT length, tested for 128, 512, 2048

inout_buffer

in/ou

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)

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