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#include "SKP_Silk_SigProc_FIX.h"

/* Apply sine window to signal vector.                                      */
/* Window types:                                                            */
/*    0 -> sine window from 0 to pi                                         */
/*    1 -> sine window from 0 to pi/2                                       */
/*    2 -> sine window from pi/2 to pi                                      */
/* every other sample of window is linearly interpolated, for speed         */
void SKP_Silk_apply_sine_window(
    SKP_int16                        px_win[],            /* O    Pointer to windowed signal                  */
    const SKP_int16                  px[],                /* I    Pointer to input signal                     */
    const SKP_int                    win_type,            /* I    Selects a window type                       */
    const SKP_int                    length               /* I    Window length, multiple of 4                */
)
{
    SKP_int   k;
    SKP_int32 f_Q16, c_Q20, S0_Q16, S1_Q16;
    /* Length must be multiple of 4 */
    SKP_assert( ( length & 3 ) == 0 );

    /* Input pointer must be 4-byte aligned */
    SKP_assert( ( (SKP_int64)px & 3 ) == 0 );

    if( win_type == 0 ) {
        f_Q16 = SKP_DIV32_16( 411775, length + 1 );        // 411775 = 2 * 65536 * pi
    } else {
        f_Q16 = SKP_DIV32_16( 205887, length + 1 );        // 205887 = 65536 * pi
    }

    /* factor used for cosine approximation */
    c_Q20 = -SKP_RSHIFT( SKP_MUL( f_Q16, f_Q16 ), 12 );

    /* c_Q20 becomes too large if length is too small */
    SKP_assert( c_Q20 >= -32768 );

    /* initialize state */
    if( win_type < 2 ) {
        /* start from 0 */
        S0_Q16 = 0;
        /* approximation of sin(f) */
        S1_Q16 = f_Q16;
    } else {
        /* start from 1 */
        S0_Q16 = ( 1 << 16 );
        /* approximation of cos(f) */
        S1_Q16 = ( 1 << 16 ) + SKP_RSHIFT( c_Q20, 5 );
    }


    /* Uses the recursive equation:   sin(n*f) = 2 * cos(f) * sin((n-1)*f) - sin((n-2)*f)    */
    /* 4 samples at a time */
    for( k = 0; k < length; k += 4 ) {
        px_win[ k ]     = (SKP_int16)SKP_SMULWB( SKP_RSHIFT( S0_Q16 + S1_Q16, 1 ), px[ k ] );
        px_win[ k + 1 ] = (SKP_int16)SKP_SMULWB( S1_Q16, px[ k + 1] );
        S0_Q16 = SKP_RSHIFT( SKP_MUL( c_Q20, S1_Q16 ), 20 ) + SKP_LSHIFT( S1_Q16, 1 ) - S0_Q16 + 1;
        S0_Q16 = SKP_min( S0_Q16, ( 1 << 16 ) );

        px_win[ k + 2 ] = (SKP_int16)SKP_SMULWB( SKP_RSHIFT( S0_Q16 + S1_Q16, 1 ), px[ k + 2] );
        px_win[ k + 3 ] = (SKP_int16)SKP_SMULWB( S0_Q16, px[ k + 3 ] );
        S1_Q16 = SKP_RSHIFT( SKP_MUL( c_Q20, S0_Q16 ), 20 ) + SKP_LSHIFT( S0_Q16, 1 ) - S1_Q16;
        S1_Q16 = SKP_min( S1_Q16, ( 1 << 16 ) );
    }
}
