michael@0: /***********************************************************************
michael@0: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
michael@0: Redistribution and use in source and binary forms, with or without
michael@0: modification, are permitted provided that the following conditions
michael@0: are met:
michael@0: - Redistributions of source code must retain the above copyright notice,
michael@0: this list of conditions and the following disclaimer.
michael@0: - Redistributions in binary form must reproduce the above copyright
michael@0: notice, this list of conditions and the following disclaimer in the
michael@0: documentation and/or other materials provided with the distribution.
michael@0: - Neither the name of Internet Society, IETF or IETF Trust, nor the
michael@0: names of specific contributors, may be used to endorse or promote
michael@0: products derived from this software without specific prior written
michael@0: permission.
michael@0: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
michael@0: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
michael@0: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
michael@0: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
michael@0: LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
michael@0: CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
michael@0: SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
michael@0: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
michael@0: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
michael@0: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
michael@0: POSSIBILITY OF SUCH DAMAGE.
michael@0: ***********************************************************************/
michael@0: 
michael@0: #ifdef HAVE_CONFIG_H
michael@0: #include "config.h"
michael@0: #endif
michael@0: 
michael@0: #include "main_FLP.h"
michael@0: 
michael@0: /* Apply sine window to signal vector   */
michael@0: /* Window types:                        */
michael@0: /*  1 -> sine window from 0 to pi/2     */
michael@0: /*  2 -> sine window from pi/2 to pi    */
michael@0: void silk_apply_sine_window_FLP(
michael@0:     silk_float                      px_win[],                           /* O    Pointer to windowed signal                  */
michael@0:     const silk_float                px[],                               /* I    Pointer to input signal                     */
michael@0:     const opus_int                  win_type,                           /* I    Selects a window type                       */
michael@0:     const opus_int                  length                              /* I    Window length, multiple of 4                */
michael@0: )
michael@0: {
michael@0:     opus_int   k;
michael@0:     silk_float freq, c, S0, S1;
michael@0: 
michael@0:     silk_assert( win_type == 1 || win_type == 2 );
michael@0: 
michael@0:     /* Length must be multiple of 4 */
michael@0:     silk_assert( ( length & 3 ) == 0 );
michael@0: 
michael@0:     freq = PI / ( length + 1 );
michael@0: 
michael@0:     /* Approximation of 2 * cos(f) */
michael@0:     c = 2.0f - freq * freq;
michael@0: 
michael@0:     /* Initialize state */
michael@0:     if( win_type < 2 ) {
michael@0:         /* Start from 0 */
michael@0:         S0 = 0.0f;
michael@0:         /* Approximation of sin(f) */
michael@0:         S1 = freq;
michael@0:     } else {
michael@0:         /* Start from 1 */
michael@0:         S0 = 1.0f;
michael@0:         /* Approximation of cos(f) */
michael@0:         S1 = 0.5f * c;
michael@0:     }
michael@0: 
michael@0:     /* Uses the recursive equation:   sin(n*f) = 2 * cos(f) * sin((n-1)*f) - sin((n-2)*f)   */
michael@0:     /* 4 samples at a time */
michael@0:     for( k = 0; k < length; k += 4 ) {
michael@0:         px_win[ k + 0 ] = px[ k + 0 ] * 0.5f * ( S0 + S1 );
michael@0:         px_win[ k + 1 ] = px[ k + 1 ] * S1;
michael@0:         S0 = c * S1 - S0;
michael@0:         px_win[ k + 2 ] = px[ k + 2 ] * 0.5f * ( S1 + S0 );
michael@0:         px_win[ k + 3 ] = px[ k + 3 ] * S0;
michael@0:         S1 = c * S0 - S1;
michael@0:     }
michael@0: }