RM0020 datasheet(23/69 Pages) STMICROELECTRONICS

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RM0020

Function API

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Arguments:

Description:

Split function of N-point real to complex float in-place fast Fourier transform (FFT).

Input data are stored in y, output data are written over the input data into y. The

function gives the first half of the output spectrum.

The calculation of the N/2 item is configurable by constant definition in the function

source file:

.set

N2_REALPART,

#/* 0/1 - real part of N/2

item isn't/is inserted in imaginary part of 0th item, default

value is 0 */

By default the N/2 output item is not calculated.

Table 9.

fft_real_split_float arguments

FFT length, tested for 128, 256, 512, 1024, 2048, 4096

in/out

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

word aligned

input: as input pass the output from the complex to complex float FFT

of half the length, data ordered x_Re(0) x_Im(0) x_Re(1) x_Im(1)...

x_Re(N/2-1) x_Im(N/2-1)

output memory layout:

X_Re(0) {0 or X_Re(N/2)} X_Re(1) X_Im(1) ... X_Re(N/2-1)

X_Im(N/2-1)

(Re - real part, Im - imaginary part)

pointer to the wa vector of twiddle factors of length N/4+1, vector

must be double word aligned

memory layout:

wa_Re(0) wa_Im(0) wa_Re(1) wa_Im(1) ... wa_Re(N/4+1)

wa_Im(N/4+1)

Use predefined wa_table_float_N arrays.

The wa_table_float_N is computed according to this formula:

for k = 0, 1, ... N/4+1

, where i is the imaginary unit

pointer to the wb vector of twiddle factors of length N/4+1, vector

must be double word aligned

memory layout:

wb_Re(0) wb_Im(0) wb_Re(1) wb_Im(1) ... wb_Re(N/4+1)

wb_Im(N/4+1)

Use predefined wb_table_float_N arrays.

The wb_table_float_N is computed according to this formula:

for k = 0, 1, ... N/4+1

, where i is the imaginary unit

wa k



--- 1iW

–







------

–

wb k



--- 1iW







------

–

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