Add copy of opus library in deps/third_party.

opus/silk/resampler_down2.c

+/***********************************************************************
+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_rom.h"
+
+/* Downsample by a factor 2 */
+void silk_resampler_down2(
+    opus_int32                  *S,                 /* I/O  State vector [ 2 ]                                          */
+    opus_int16                  *out,               /* O    Output signal [ len ]                                       */
+    const opus_int16            *in,                /* I    Input signal [ floor(len/2) ]                               */
+    opus_int32                  inLen               /* I    Number of input samples                                     */
+)
+{
+    opus_int32 k, len2 = silk_RSHIFT32( inLen, 1 );
+    opus_int32 in32, out32, Y, X;
+
+    silk_assert( silk_resampler_down2_0 > 0 );
+    silk_assert( silk_resampler_down2_1 < 0 );
+
+    /* Internal variables and state are in Q10 format */
+    for( k = 0; k < len2; k++ ) {
+        /* Convert to Q10 */
+        in32 = silk_LSHIFT( (opus_int32)in[ 2 * k ], 10 );
+
+        /* All-pass section for even input sample */
+        Y      = silk_SUB32( in32, S[ 0 ] );
+        X      = silk_SMLAWB( Y, Y, silk_resampler_down2_1 );
+        out32  = silk_ADD32( S[ 0 ], X );
+        S[ 0 ] = silk_ADD32( in32, X );
+
+        /* Convert to Q10 */
+        in32 = silk_LSHIFT( (opus_int32)in[ 2 * k + 1 ], 10 );
+
+        /* All-pass section for odd input sample, and add to output of previous section */
+        Y      = silk_SUB32( in32, S[ 1 ] );
+        X      = silk_SMULWB( Y, silk_resampler_down2_0 );
+        out32  = silk_ADD32( out32, S[ 1 ] );
+        out32  = silk_ADD32( out32, X );
+        S[ 1 ] = silk_ADD32( in32, X );
+
+        /* Add, convert back to int16 and store to output */
+        out[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( out32, 11 ) );
+    }
+}
+