cannam@154: /***********************************************************************
cannam@154: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
cannam@154: Redistribution and use in source and binary forms, with or without
cannam@154: modification, are permitted provided that the following conditions
cannam@154: are met:
cannam@154: - Redistributions of source code must retain the above copyright notice,
cannam@154: this list of conditions and the following disclaimer.
cannam@154: - Redistributions in binary form must reproduce the above copyright
cannam@154: notice, this list of conditions and the following disclaimer in the
cannam@154: documentation and/or other materials provided with the distribution.
cannam@154: - Neither the name of Internet Society, IETF or IETF Trust, nor the
cannam@154: names of specific contributors, may be used to endorse or promote
cannam@154: products derived from this software without specific prior written
cannam@154: permission.
cannam@154: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
cannam@154: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
cannam@154: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
cannam@154: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
cannam@154: LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
cannam@154: CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
cannam@154: SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
cannam@154: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
cannam@154: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
cannam@154: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
cannam@154: POSSIBILITY OF SUCH DAMAGE.
cannam@154: ***********************************************************************/
cannam@154: 
cannam@154: #ifdef HAVE_CONFIG_H
cannam@154: #include "config.h"
cannam@154: #endif
cannam@154: 
cannam@154: #include "SigProc_FIX.h"
cannam@154: #include "resampler_rom.h"
cannam@154: 
cannam@154: /* Downsample by a factor 2 */
cannam@154: void silk_resampler_down2(
cannam@154:     opus_int32                  *S,                 /* I/O  State vector [ 2 ]                                          */
cannam@154:     opus_int16                  *out,               /* O    Output signal [ floor(len/2) ]                              */
cannam@154:     const opus_int16            *in,                /* I    Input signal [ len ]                                        */
cannam@154:     opus_int32                  inLen               /* I    Number of input samples                                     */
cannam@154: )
cannam@154: {
cannam@154:     opus_int32 k, len2 = silk_RSHIFT32( inLen, 1 );
cannam@154:     opus_int32 in32, out32, Y, X;
cannam@154: 
cannam@154:     celt_assert( silk_resampler_down2_0 > 0 );
cannam@154:     celt_assert( silk_resampler_down2_1 < 0 );
cannam@154: 
cannam@154:     /* Internal variables and state are in Q10 format */
cannam@154:     for( k = 0; k < len2; k++ ) {
cannam@154:         /* Convert to Q10 */
cannam@154:         in32 = silk_LSHIFT( (opus_int32)in[ 2 * k ], 10 );
cannam@154: 
cannam@154:         /* All-pass section for even input sample */
cannam@154:         Y      = silk_SUB32( in32, S[ 0 ] );
cannam@154:         X      = silk_SMLAWB( Y, Y, silk_resampler_down2_1 );
cannam@154:         out32  = silk_ADD32( S[ 0 ], X );
cannam@154:         S[ 0 ] = silk_ADD32( in32, X );
cannam@154: 
cannam@154:         /* Convert to Q10 */
cannam@154:         in32 = silk_LSHIFT( (opus_int32)in[ 2 * k + 1 ], 10 );
cannam@154: 
cannam@154:         /* All-pass section for odd input sample, and add to output of previous section */
cannam@154:         Y      = silk_SUB32( in32, S[ 1 ] );
cannam@154:         X      = silk_SMULWB( Y, silk_resampler_down2_0 );
cannam@154:         out32  = silk_ADD32( out32, S[ 1 ] );
cannam@154:         out32  = silk_ADD32( out32, X );
cannam@154:         S[ 1 ] = silk_ADD32( in32, X );
cannam@154: 
cannam@154:         /* Add, convert back to int16 and store to output */
cannam@154:         out[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( out32, 11 ) );
cannam@154:     }
cannam@154: }
cannam@154: