ref: 310af750eb5726b4143a43208f2bc03677c6f5db
dir: /silk/SKP_Silk_apply_sine_window_FLP.c/
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#include "SKP_Silk_main_FLP.h"
/* Apply sine window to signal vector. */
/* Window types: */
/* 1 -> sine window from 0 to pi/2 */
/* 2 -> sine window from pi/2 to pi */
void SKP_Silk_apply_sine_window_FLP(
SKP_float px_win[], /* O Pointer to windowed signal */
const SKP_float px[], /* I Pointer to input signal */
const SKP_int win_type, /* I Selects a window type */
const SKP_int length /* I Window length, multiple of 4 */
)
{
SKP_int k;
SKP_float freq, c, S0, S1;
SKP_assert( win_type == 1 || win_type == 2 );
/* Length must be multiple of 4 */
SKP_assert( ( length & 3 ) == 0 );
freq = PI / ( length + 1 );
/* Approximation of 2 * cos(f) */
c = 2.0f - freq * freq;
/* Initialize state */
if( win_type < 2 ) {
/* Start from 0 */
S0 = 0.0f;
/* Approximation of sin(f) */
S1 = freq;
} else {
/* Start from 1 */
S0 = 1.0f;
/* Approximation of cos(f) */
S1 = 0.5f * c;
}
/* Uses the recursive equation: sin(n*f) = 2 * cos(f) * sin((n-1)*f) - sin((n-2)*f) */
/* 4 samples at a time */
for( k = 0; k < length; k += 4 ) {
px_win[ k + 0 ] = px[ k + 0 ] * 0.5f * ( S0 + S1 );
px_win[ k + 1 ] = px[ k + 1 ] * S1;
S0 = c * S1 - S0;
px_win[ k + 2 ] = px[ k + 2 ] * 0.5f * ( S1 + S0 );
px_win[ k + 3 ] = px[ k + 3 ] * S0;
S1 = c * S0 - S1;
}
}