Add copy of opus library in deps/third_party.

opus/silk/interpolate.c

+/***********************************************************************
+Copyright (c) 2006-2011, Skype Limited. All rights reserved.
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+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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+***********************************************************************/
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "main.h"
+
+/* Interpolate two vectors */
+void silk_interpolate(
+    opus_int16                  xi[ MAX_LPC_ORDER ],            /* O    interpolated vector                         */
+    const opus_int16            x0[ MAX_LPC_ORDER ],            /* I    first vector                                */
+    const opus_int16            x1[ MAX_LPC_ORDER ],            /* I    second vector                               */
+    const opus_int              ifact_Q2,                       /* I    interp. factor, weight on 2nd vector        */
+    const opus_int              d                               /* I    number of parameters                        */
+)
+{
+    opus_int i;
+
+    silk_assert( ifact_Q2 >= 0 );
+    silk_assert( ifact_Q2 <= 4 );
+
+    for( i = 0; i < d; i++ ) {
+        xi[ i ] = (opus_int16)silk_ADD_RSHIFT( x0[ i ], silk_SMULBB( x1[ i ] - x0[ i ], ifact_Q2 ), 2 );
+    }
+}