[Opus] Update to v1.2.1

third_party/opus/src/silk/fixed/k2a_FIX.c

Index: third_party/opus/src/silk/fixed/k2a_FIX.c
diff --git a/third_party/opus/src/silk/fixed/k2a_FIX.c b/third_party/opus/src/silk/fixed/k2a_FIX.c
index 5fee599bcb74305a1d45c41e8795a0ee3f9cb5d9..549f6eadaa29de85bfd4c267c79259c6c114a9d9 100644
--- a/third_party/opus/src/silk/fixed/k2a_FIX.c
+++ b/third_party/opus/src/silk/fixed/k2a_FIX.c
@@ -39,14 +39,15 @@ void silk_k2a(
 )
 {
     opus_int   k, n;
-    opus_int32 Atmp[ SILK_MAX_ORDER_LPC ];
+    opus_int32 rc, tmp1, tmp2;
 
     for( k = 0; k < order; k++ ) {
-        for( n = 0; n < k; n++ ) {
-            Atmp[ n ] = A_Q24[ n ];
-        }
-        for( n = 0; n < k; n++ ) {
-            A_Q24[ n ] = silk_SMLAWB( A_Q24[ n ], silk_LSHIFT( Atmp[ k - n - 1 ], 1 ), rc_Q15[ k ] );
+        rc = rc_Q15[ k ];
+        for( n = 0; n < (k + 1) >> 1; n++ ) {
+            tmp1 = A_Q24[ n ];
+            tmp2 = A_Q24[ k - n - 1 ];
+            A_Q24[ n ]         = silk_SMLAWB( tmp1, silk_LSHIFT( tmp2, 1 ), rc );
+            A_Q24[ k - n - 1 ] = silk_SMLAWB( tmp2, silk_LSHIFT( tmp1, 1 ), rc );
         }
         A_Q24[ k ] = -silk_LSHIFT( (opus_int32)rc_Q15[ k ], 9 );
     }