Disabling the use of celt_fir() in silk_LPC_analysis_filter() by default

silk/LPC_analysis_filter.c

@@ -39,6 +39,13 @@ POSSIBILITY OF SUCH DAMAGE.
 /* first d output samples are set to zero  */
 /*******************************************/
 
+/* OPT: Using celt_fir() for this function should be faster, but it may cause
+   integer overflows in intermediate values (not final results), which the
+   current implementation silences by casting to unsigned. Enabling
+   this should be safe in pretty much all cases, even though it is not technically
+   C89-compliant. */
+#define USE_CELT_FIR 0
+
 void silk_LPC_analysis_filter(
     opus_int16                  *out,               /* O    Output signal                                               */
     const opus_int16            *in,                /* I    Input signal                                                */
@@ -49,7 +56,7 @@ void silk_LPC_analysis_filter(
 )
 {
     opus_int   j;
-#ifdef FIXED_POINT
+#if USE_CELT_FIR
     opus_int16 mem[SILK_MAX_ORDER_LPC];
     opus_int16 num[SILK_MAX_ORDER_LPC];
 #else
@@ -62,7 +69,7 @@ void silk_LPC_analysis_filter(
     silk_assert( (d & 1) == 0 );
     silk_assert( d <= len );
 
-#ifdef FIXED_POINT
+#if USE_CELT_FIR
     silk_assert( d <= SILK_MAX_ORDER_LPC );
     for ( j = 0; j < d; j++ ) {
         num[ j ] = -B[ j ];