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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