ref: 8ff61171250502a6059995c05902caf06ab07acf
dir: /silk/silk_apply_sine_window.c/
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#include "silk_SigProc_FIX.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 */
/* Every other sample is linearly interpolated, for speed. */
/* Window length must be between 16 and 120 (incl) and a multiple of 4. */
/* Matlab code for table:
for k=16:9*4:16+2*9*4, fprintf(' %7.d,', -round(65536*pi ./ (k:4:k+8*4))); fprintf('\n'); end
*/
static SKP_int16 freq_table_Q16[ 27 ] = {
12111, 9804, 8235, 7100, 6239, 5565, 5022, 4575, 4202,
3885, 3612, 3375, 3167, 2984, 2820, 2674, 2542, 2422,
2313, 2214, 2123, 2038, 1961, 1889, 1822, 1760, 1702,
};
void silk_apply_sine_window(
SKP_int16 px_win[], /* O Pointer to windowed signal */
const SKP_int16 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, f_Q16, c_Q16;
SKP_int32 S0_Q16, S1_Q16;
SKP_assert( win_type == 1 || win_type == 2 );
/* Length must be in a range from 16 to 120 and a multiple of 4 */
SKP_assert( length >= 16 && length <= 120 );
SKP_assert( ( length & 3 ) == 0 );
/* Frequency */
k = ( length >> 2 ) - 4;
SKP_assert( k >= 0 && k <= 26 );
f_Q16 = (SKP_int)freq_table_Q16[ k ];
/* Factor used for cosine approximation */
c_Q16 = SKP_SMULWB( f_Q16, -f_Q16 );
SKP_assert( c_Q16 >= -32768 );
/* initialize state */
if( win_type == 1 ) {
/* start from 0 */
S0_Q16 = 0;
/* approximation of sin(f) */
S1_Q16 = f_Q16 + SKP_RSHIFT( length, 3 );
} else {
/* start from 1 */
S0_Q16 = ( 1 << 16 );
/* approximation of cos(f) */
S1_Q16 = ( 1 << 16 ) + SKP_RSHIFT( c_Q16, 1 ) + SKP_RSHIFT( length, 4 );
}
/* 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 ] = (SKP_int16)SKP_SMULWB( SKP_RSHIFT( S0_Q16 + S1_Q16, 1 ), px[ k ] );
px_win[ k + 1 ] = (SKP_int16)SKP_SMULWB( S1_Q16, px[ k + 1] );
S0_Q16 = SKP_SMULWB( S1_Q16, c_Q16 ) + SKP_LSHIFT( S1_Q16, 1 ) - S0_Q16 + 1;
S0_Q16 = SKP_min( S0_Q16, ( 1 << 16 ) );
px_win[ k + 2 ] = (SKP_int16)SKP_SMULWB( SKP_RSHIFT( S0_Q16 + S1_Q16, 1 ), px[ k + 2] );
px_win[ k + 3 ] = (SKP_int16)SKP_SMULWB( S0_Q16, px[ k + 3 ] );
S1_Q16 = SKP_SMULWB( S0_Q16, c_Q16 ) + SKP_LSHIFT( S0_Q16, 1 ) - S1_Q16;
S1_Q16 = SKP_min( S1_Q16, ( 1 << 16 ) );
}
}