Fix UBSan errors (signed integer overflow)

webrtc/modules/audio_coding/codecs/ilbc/smooth.c

Index: webrtc/modules/audio_coding/codecs/ilbc/smooth.c
diff --git a/webrtc/modules/audio_coding/codecs/ilbc/smooth.c b/webrtc/modules/audio_coding/codecs/ilbc/smooth.c
index 58b37ee31cc99a4959c8f1f1b5d4ea93521bdd96..269331cce4d4b7d00f4daccc0c9819ee6afd5c97 100644
--- a/webrtc/modules/audio_coding/codecs/ilbc/smooth.c
+++ b/webrtc/modules/audio_coding/codecs/ilbc/smooth.c
@@ -31,7 +31,7 @@ void WebRtcIlbcfix_Smooth(
     int16_t *surround  /* (i) The approximation from the
                                 surrounding sequences */
                           ) {
-  int16_t maxtot, scale, scale1, scale2;
+  int16_t scale, scale1, scale2;
   int16_t A, B, C, denomW16;
   int32_t B_W32, denom, num;
   int32_t errs;
@@ -40,18 +40,21 @@ void WebRtcIlbcfix_Smooth(
   int16_t w11prim;
   int16_t bitsw00, bitsw10, bitsw11;
   int32_t w11w00, w10w10, w00w00;
-  int16_t max1, max2;
+  uint32_t max1, max2, max12;
 
   /* compute some inner products (ensure no overflow by first calculating proper scale factor) */
 
   w00 = w10 = w11 = 0;
 
-  max1=WebRtcSpl_MaxAbsValueW16(current, ENH_BLOCKL);
-  max2=WebRtcSpl_MaxAbsValueW16(surround, ENH_BLOCKL);
-  maxtot=WEBRTC_SPL_MAX(max1, max2);
-
-  scale=WebRtcSpl_GetSizeInBits(maxtot);
-  scale = (int16_t)(2 * scale) - 26;
+  // Calculate a right shift that will let us sum ENH_BLOCKL pairwise products
+  // of values from the two sequences without overflowing an int32_t. (The +1
+  // in max1 and max2 are because WebRtcSpl_MaxAbsValueW16 will return 2**15 -
+  // 1 if the input array contains -2**15.)
+  max1 = WebRtcSpl_MaxAbsValueW16(current, ENH_BLOCKL) + 1;
+  max2 = WebRtcSpl_MaxAbsValueW16(surround, ENH_BLOCKL) + 1;
+  max12 = WEBRTC_SPL_MAX(max1, max2);
+  scale = (64 - 31) -
+          WebRtcSpl_CountLeadingZeros64((max12 * max12) * (uint64_t)ENH_BLOCKL);
   scale=WEBRTC_SPL_MAX(0, scale);
 
   w00=WebRtcSpl_DotProductWithScale(current,current,ENH_BLOCKL,scale);