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27 
28 #ifdef HAVE_CONFIG_H
29 #include "config.h"
30 #endif
31 
32 #include "main_FLP.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    */
silk_apply_sine_window_FLP(silk_float px_win[],const silk_float px[],const opus_int win_type,const opus_int length)38 void silk_apply_sine_window_FLP(
39     silk_float                      px_win[],                           /* O    Pointer to windowed signal                  */
40     const silk_float                px[],                               /* I    Pointer to input signal                     */
41     const opus_int                  win_type,                           /* I    Selects a window type                       */
42     const opus_int                  length                              /* I    Window length, multiple of 4                */
43 )
44 {
45     opus_int   k;
46     silk_float freq, c, S0, S1;
47 
48     silk_assert( win_type == 1 || win_type == 2 );
49 
50     /* Length must be multiple of 4 */
51     silk_assert( ( length & 3 ) == 0 );
52 
53     freq = PI / ( length + 1 );
54 
55     /* Approximation of 2 * cos(f) */
56     c = 2.0f - freq * freq;
57 
58     /* Initialize state */
59     if( win_type < 2 ) {
60         /* Start from 0 */
61         S0 = 0.0f;
62         /* Approximation of sin(f) */
63         S1 = freq;
64     } else {
65         /* Start from 1 */
66         S0 = 1.0f;
67         /* Approximation of cos(f) */
68         S1 = 0.5f * c;
69     }
70 
71     /* Uses the recursive equation:   sin(n*f) = 2 * cos(f) * sin((n-1)*f) - sin((n-2)*f)   */
72     /* 4 samples at a time */
73     for( k = 0; k < length; k += 4 ) {
74         px_win[ k + 0 ] = px[ k + 0 ] * 0.5f * ( S0 + S1 );
75         px_win[ k + 1 ] = px[ k + 1 ] * S1;
76         S0 = c * S1 - S0;
77         px_win[ k + 2 ] = px[ k + 2 ] * 0.5f * ( S1 + S0 );
78         px_win[ k + 3 ] = px[ k + 3 ] * S0;
79         S1 = c * S0 - S1;
80     }
81 }
82