Chris@69: /***********************************************************************
Chris@69: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
Chris@69: Redistribution and use in source and binary forms, with or without
Chris@69: modification, are permitted provided that the following conditions
Chris@69: are met:
Chris@69: - Redistributions of source code must retain the above copyright notice,
Chris@69: this list of conditions and the following disclaimer.
Chris@69: - Redistributions in binary form must reproduce the above copyright
Chris@69: notice, this list of conditions and the following disclaimer in the
Chris@69: documentation and/or other materials provided with the distribution.
Chris@69: - Neither the name of Internet Society, IETF or IETF Trust, nor the
Chris@69: names of specific contributors, may be used to endorse or promote
Chris@69: products derived from this software without specific prior written
Chris@69: permission.
Chris@69: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
Chris@69: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
Chris@69: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
Chris@69: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
Chris@69: LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
Chris@69: CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
Chris@69: SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
Chris@69: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
Chris@69: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
Chris@69: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
Chris@69: POSSIBILITY OF SUCH DAMAGE.
Chris@69: ***********************************************************************/
Chris@69: 
Chris@69: #ifdef HAVE_CONFIG_H
Chris@69: #include "config.h"
Chris@69: #endif
Chris@69: 
Chris@69: #include "SigProc_FIX.h"
Chris@69: #include "resampler_rom.h"
Chris@69: 
Chris@69: /* Downsample by a factor 2 */
Chris@69: void silk_resampler_down2(
Chris@69:     opus_int32                  *S,                 /* I/O  State vector [ 2 ]                                          */
Chris@69:     opus_int16                  *out,               /* O    Output signal [ floor(len/2) ]                              */
Chris@69:     const opus_int16            *in,                /* I    Input signal [ len ]                                        */
Chris@69:     opus_int32                  inLen               /* I    Number of input samples                                     */
Chris@69: )
Chris@69: {
Chris@69:     opus_int32 k, len2 = silk_RSHIFT32( inLen, 1 );
Chris@69:     opus_int32 in32, out32, Y, X;
Chris@69: 
Chris@69:     celt_assert( silk_resampler_down2_0 > 0 );
Chris@69:     celt_assert( silk_resampler_down2_1 < 0 );
Chris@69: 
Chris@69:     /* Internal variables and state are in Q10 format */
Chris@69:     for( k = 0; k < len2; k++ ) {
Chris@69:         /* Convert to Q10 */
Chris@69:         in32 = silk_LSHIFT( (opus_int32)in[ 2 * k ], 10 );
Chris@69: 
Chris@69:         /* All-pass section for even input sample */
Chris@69:         Y      = silk_SUB32( in32, S[ 0 ] );
Chris@69:         X      = silk_SMLAWB( Y, Y, silk_resampler_down2_1 );
Chris@69:         out32  = silk_ADD32( S[ 0 ], X );
Chris@69:         S[ 0 ] = silk_ADD32( in32, X );
Chris@69: 
Chris@69:         /* Convert to Q10 */
Chris@69:         in32 = silk_LSHIFT( (opus_int32)in[ 2 * k + 1 ], 10 );
Chris@69: 
Chris@69:         /* All-pass section for odd input sample, and add to output of previous section */
Chris@69:         Y      = silk_SUB32( in32, S[ 1 ] );
Chris@69:         X      = silk_SMULWB( Y, silk_resampler_down2_0 );
Chris@69:         out32  = silk_ADD32( out32, S[ 1 ] );
Chris@69:         out32  = silk_ADD32( out32, X );
Chris@69:         S[ 1 ] = silk_ADD32( in32, X );
Chris@69: 
Chris@69:         /* Add, convert back to int16 and store to output */
Chris@69:         out[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( out32, 11 ) );
Chris@69:     }
Chris@69: }
Chris@69: