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Allow wrap-around in silk_LPC_analysis_filter()

--- a/silk/LPC_analysis_filter.c

+++ b/silk/LPC_analysis_filter.c

@@ -58,18 +58,20 @@

         in_ptr = &in[ ix - 1 ];

         out32_Q12 = silk_SMULBB(            in_ptr[  0 ], B[ 0 ] );

-        out32_Q12 = silk_SMLABB( out32_Q12, in_ptr[ -1 ], B[ 1 ] );

-        out32_Q12 = silk_SMLABB( out32_Q12, in_ptr[ -2 ], B[ 2 ] );

-        out32_Q12 = silk_SMLABB( out32_Q12, in_ptr[ -3 ], B[ 3 ] );

-        out32_Q12 = silk_SMLABB( out32_Q12, in_ptr[ -4 ], B[ 4 ] );

-        out32_Q12 = silk_SMLABB( out32_Q12, in_ptr[ -5 ], B[ 5 ] );

+        /* Allowing wrap around so that two wraps can cancel each other. The rare

+           cases where the result wraps around can only be triggered by invalid streams*/

+        out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -1 ], B[ 1 ] );

+        out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -2 ], B[ 2 ] );

+        out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -3 ], B[ 3 ] );

+        out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -4 ], B[ 4 ] );

+        out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -5 ], B[ 5 ] );

         for( j = 6; j < d; j += 2 ) {

-            out32_Q12 = silk_SMLABB( out32_Q12, in_ptr[ -j     ], B[ j     ] );

-            out32_Q12 = silk_SMLABB( out32_Q12, in_ptr[ -j - 1 ], B[ j + 1 ] );

+            out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -j     ], B[ j     ] );

+            out32_Q12 = silk_SMLABB_ovflw( out32_Q12, in_ptr[ -j - 1 ], B[ j + 1 ] );

         }

         /* Subtract prediction */

-        out32_Q12 = silk_SUB32( silk_LSHIFT( (opus_int32)in_ptr[ 1 ], 12 ), out32_Q12 );

+        out32_Q12 = silk_SUB32_ovflw( silk_LSHIFT( (opus_int32)in_ptr[ 1 ], 12 ), out32_Q12 );

         /* Scale to Q0 */

         out32 = silk_RSHIFT_ROUND( out32_Q12, 12 );

--- a/silk/SigProc_FIX.h

+++ b/silk/SigProc_FIX.h

@@ -421,6 +421,9 @@

    (just standard two's complement implementation-specific behaviour) */

 #define silk_SUB32_ovflw(a, b)              ((opus_int32)((opus_uint32)(a) - (opus_uint32)(b)))

+/* a32 + (opus_int32)((opus_int16)(b32)) * (opus_int32)((opus_int16)(c32)) output have to be 32bit int */

+#define silk_SMLABB_ovflw(a32, b32, c32)       (silk_ADD32_ovflw((a32) , ((opus_int32)((opus_int16)(b32))) * (opus_int32)((opus_int16)(c32))))

+

 /* Multiply-accumulate macros that allow overflow in the addition (ie, no asserts in debug mode)*/

 #define silk_MLA_ovflw(a32, b32, c32)       silk_ADD32_ovflw((a32), (opus_uint32)(b32) * (opus_uint32)(c32))

 #ifndef silk_SMLABB_ovflw