RM0020 datasheet(30/69 Pages) STMICROELECTRONICS

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Function API

RM0020

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are written into y vector. The y vector can be the same as x vector (in-place

windowing).

The output scaling is configurable by constant definition in the function source file:

.set

SCALING,

#/* 0 - off, 1 - on (output

divided by 2) */

By default it is turned on. The scaling is performed by dividing output data by 2.

Algorithm:

Equation 26

for each k = 0,1,...N-1

where x denotes complex multiplication. The output value

is divided by 2 when

SCALING == 1.

Note: There must be 8 bytes of readable memory behind x and w buffers.

If SCALING == 1, then w array mustn't have any value equal to -1 (-32768) since

there is used integer multiplication for fractional data.

Performance: See Section 7 and Table 43.

Example 12. window_apply_complex_frac16

#include "libdsp2.h"

short x[2*64+4];

/* +4 to ensure there is 8 bytes of readable

memory behind buffer, must be aligned to 4 bytes */

short w[2*64+4];

/* +4 to ensure there is 8 bytes of readable

memory behind buffer, must be aligned to 4 bytes */

void main(void)

{

unsigned int i, N;

/* length of complex vectors is 64 */

N = 64;

/* prepare example input data */

for (i = 0; i < 2*N; i++) x[i] = (i+1)<<5;

for (i = 0; i < 2*N; i++) w[i] = (i+2*N)<<5;

/* windowing function on complex frac16 data, x[i] = x[i]*w[i]

window_apply_complex_frac16(N, x, x, w);

}

6.13

Real float windowing function

Function call:

void window_apply_real_float(unsigned int N, float *x, float *y,

float *w);

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