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26***********************************************************************/
27
28#ifdef HAVE_CONFIG_H
29#include "config.h"
30#endif
31
32#include "SigProc_FIX.h"
33
34/* Apply sine window to signal vector.                                      */
35/* Window types:                                                            */
36/*    1 -> sine window from 0 to pi/2                                       */
37/*    2 -> sine window from pi/2 to pi                                      */
38/* Every other sample is linearly interpolated, for speed.                  */
39/* Window length must be between 16 and 120 (incl) and a multiple of 4.     */
40
41/* Matlab code for table:
42   for k=16:9*4:16+2*9*4, fprintf(' %7.d,', -round(65536*pi ./ (k:4:k+8*4))); fprintf('\n'); end
43*/
44static const opus_int16 freq_table_Q16[ 27 ] = {
45   12111,    9804,    8235,    7100,    6239,    5565,    5022,    4575,    4202,
46    3885,    3612,    3375,    3167,    2984,    2820,    2674,    2542,    2422,
47    2313,    2214,    2123,    2038,    1961,    1889,    1822,    1760,    1702,
48};
49
50void silk_apply_sine_window(
51    opus_int16                  px_win[],           /* O    Pointer to windowed signal                                  */
52    const opus_int16            px[],               /* I    Pointer to input signal                                     */
53    const opus_int              win_type,           /* I    Selects a window type                                       */
54    const opus_int              length              /* I    Window length, multiple of 4                                */
55)
56{
57    opus_int   k, f_Q16, c_Q16;
58    opus_int32 S0_Q16, S1_Q16;
59
60    silk_assert( win_type == 1 || win_type == 2 );
61
62    /* Length must be in a range from 16 to 120 and a multiple of 4 */
63    silk_assert( length >= 16 && length <= 120 );
64    silk_assert( ( length & 3 ) == 0 );
65
66    /* Frequency */
67    k = ( length >> 2 ) - 4;
68    silk_assert( k >= 0 && k <= 26 );
69    f_Q16 = (opus_int)freq_table_Q16[ k ];
70
71    /* Factor used for cosine approximation */
72    c_Q16 = silk_SMULWB( (opus_int32)f_Q16, -f_Q16 );
73    silk_assert( c_Q16 >= -32768 );
74
75    /* initialize state */
76    if( win_type == 1 ) {
77        /* start from 0 */
78        S0_Q16 = 0;
79        /* approximation of sin(f) */
80        S1_Q16 = f_Q16 + silk_RSHIFT( length, 3 );
81    } else {
82        /* start from 1 */
83        S0_Q16 = ( (opus_int32)1 << 16 );
84        /* approximation of cos(f) */
85        S1_Q16 = ( (opus_int32)1 << 16 ) + silk_RSHIFT( c_Q16, 1 ) + silk_RSHIFT( length, 4 );
86    }
87
88    /* Uses the recursive equation:   sin(n*f) = 2 * cos(f) * sin((n-1)*f) - sin((n-2)*f)    */
89    /* 4 samples at a time */
90    for( k = 0; k < length; k += 4 ) {
91        px_win[ k ]     = (opus_int16)silk_SMULWB( silk_RSHIFT( S0_Q16 + S1_Q16, 1 ), px[ k ] );
92        px_win[ k + 1 ] = (opus_int16)silk_SMULWB( S1_Q16, px[ k + 1] );
93        S0_Q16 = silk_SMULWB( S1_Q16, c_Q16 ) + silk_LSHIFT( S1_Q16, 1 ) - S0_Q16 + 1;
94        S0_Q16 = silk_min( S0_Q16, ( (opus_int32)1 << 16 ) );
95
96        px_win[ k + 2 ] = (opus_int16)silk_SMULWB( silk_RSHIFT( S0_Q16 + S1_Q16, 1 ), px[ k + 2] );
97        px_win[ k + 3 ] = (opus_int16)silk_SMULWB( S0_Q16, px[ k + 3 ] );
98        S1_Q16 = silk_SMULWB( S0_Q16, c_Q16 ) + silk_LSHIFT( S0_Q16, 1 ) - S1_Q16;
99        S1_Q16 = silk_min( S1_Q16, ( (opus_int32)1 << 16 ) );
100    }
101}
102