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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    */
     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