The Tor Browser: media/libopus/silk/fixed/apply_sine_window

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

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    26 ***********************************************************************/

    28 #ifdef HAVE_CONFIG_H

    29 #include "config.h"

    30 #endif

    32 #include "SigProc_FIX.h"

    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.     */

    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 */

    44 static 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 };

    50 void 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;

    60     silk_assert( win_type == 1 || win_type == 2 );

    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 );

    66     /* Frequency */

    67     k = ( length >> 2 ) - 4;

    68     silk_assert( k >= 0 && k <= 26 );

    69     f_Q16 = (opus_int)freq_table_Q16[ k ];

    71     /* Factor used for cosine approximation */

    72     c_Q16 = silk_SMULWB( (opus_int32)f_Q16, -f_Q16 );

    73     silk_assert( c_Q16 >= -32768 );

    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     }

    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 ) );

    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 }

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