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+/***********************************************************************
+Copyright (c) 2006-2011, Skype Limited. All rights reserved.
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+- Redistributions of source code must retain the above copyright notice,
+this list of conditions and the following disclaimer.
+- Redistributions in binary form must reproduce the above copyright
+notice, this list of conditions and the following disclaimer in the
+documentation and/or other materials provided with the distribution.
+- Neither the name of Internet Society, IETF or IETF Trust, nor the
+names of specific contributors, may be used to endorse or promote
+products derived from this software without specific prior written
+permission.
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+***********************************************************************/
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "SigProc_FIX.h"
+#include "resampler_private.h"
+#include "stack_alloc.h"
+
+#define ORDER_FIR 4
+
+/* Downsample by a factor 2/3, low quality */
+void silk_resampler_down2_3(
+ opus_int32 *S, /* I/O State vector [ 6 ] */
+ opus_int16 *out, /* O Output signal [ floor(2*inLen/3) ] */
+ const opus_int16 *in, /* I Input signal [ inLen ] */
+ opus_int32 inLen /* I Number of input samples */
+)
+{
+ opus_int32 nSamplesIn, counter, res_Q6;
+ VARDECL( opus_int32, buf );
+ opus_int32 *buf_ptr;
+ SAVE_STACK;
+
+ ALLOC( buf, RESAMPLER_MAX_BATCH_SIZE_IN + ORDER_FIR, opus_int32 );
+
+ /* Copy buffered samples to start of buffer */
+ silk_memcpy( buf, S, ORDER_FIR * sizeof( opus_int32 ) );
+
+ /* Iterate over blocks of frameSizeIn input samples */
+ while( 1 ) {
+ nSamplesIn = silk_min( inLen, RESAMPLER_MAX_BATCH_SIZE_IN );
+
+ /* Second-order AR filter (output in Q8) */
+ silk_resampler_private_AR2( &S[ ORDER_FIR ], &buf[ ORDER_FIR ], in,
+ silk_Resampler_2_3_COEFS_LQ, nSamplesIn );
+
+ /* Interpolate filtered signal */
+ buf_ptr = buf;
+ counter = nSamplesIn;
+ while( counter > 2 ) {
+ /* Inner product */
+ res_Q6 = silk_SMULWB( buf_ptr[ 0 ], silk_Resampler_2_3_COEFS_LQ[ 2 ] );
+ res_Q6 = silk_SMLAWB( res_Q6, buf_ptr[ 1 ], silk_Resampler_2_3_COEFS_LQ[ 3 ] );
+ res_Q6 = silk_SMLAWB( res_Q6, buf_ptr[ 2 ], silk_Resampler_2_3_COEFS_LQ[ 5 ] );
+ res_Q6 = silk_SMLAWB( res_Q6, buf_ptr[ 3 ], silk_Resampler_2_3_COEFS_LQ[ 4 ] );
+
+ /* Scale down, saturate and store in output array */
+ *out++ = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( res_Q6, 6 ) );
+
+ res_Q6 = silk_SMULWB( buf_ptr[ 1 ], silk_Resampler_2_3_COEFS_LQ[ 4 ] );
+ res_Q6 = silk_SMLAWB( res_Q6, buf_ptr[ 2 ], silk_Resampler_2_3_COEFS_LQ[ 5 ] );
+ res_Q6 = silk_SMLAWB( res_Q6, buf_ptr[ 3 ], silk_Resampler_2_3_COEFS_LQ[ 3 ] );
+ res_Q6 = silk_SMLAWB( res_Q6, buf_ptr[ 4 ], silk_Resampler_2_3_COEFS_LQ[ 2 ] );
+
+ /* Scale down, saturate and store in output array */
+ *out++ = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( res_Q6, 6 ) );
+
+ buf_ptr += 3;
+ counter -= 3;
+ }
+
+ in += nSamplesIn;
+ inLen -= nSamplesIn;
+
+ if( inLen > 0 ) {
+ /* More iterations to do; copy last part of filtered signal to beginning of buffer */
+ silk_memcpy( buf, &buf[ nSamplesIn ], ORDER_FIR * sizeof( opus_int32 ) );
+ } else {
+ break;
+ }
+ }
+
+ /* Copy last part of filtered signal to the state for the next call */
+ silk_memcpy( S, &buf[ nSamplesIn ], ORDER_FIR * sizeof( opus_int32 ) );
+ RESTORE_STACK;
+}