Fix UBSan errors (left shift of negative value, left shift overflows int)

webrtc/modules/audio_coding/codecs/isac/main/source/entropy_coding.c

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 144 matching lines @@
     diffQ16[n] = (CS_ptrQ9[n] * (CorrQ11[1] >> shftVal) + 2) >> 2;
   }
   for (k = 2; k < AR_ORDER; k += 2) {
     CS_ptrQ9 = WebRtcIsac_kCos[k];
     for (n = 0; n < FRAMESAMPLES / 8; n++) {
       diffQ16[n] += (CS_ptrQ9[n] * (CorrQ11[k + 1] >> shftVal) + 2) >> 2;
     }
   }
 
   for (k = 0; k < FRAMESAMPLES / 8; k++) {
-    CurveQ16[FRAMESAMPLES_QUARTER - 1 - k] = CurveQ16[k] -
-        (diffQ16[k] << shftVal);
-    CurveQ16[k] += diffQ16[k] << shftVal;
+    int32_t diff_q16_shifted = (int32_t)((uint32_t)(diffQ16[k]) << shftVal);
+    CurveQ16[FRAMESAMPLES_QUARTER - 1 - k] = CurveQ16[k] - diff_q16_shifted;
+    CurveQ16[k] += diff_q16_shifted;
   }
 }
 
 /* Generate array of dither samples in Q7. */
 static void GenerateDitherQ7Lb(int16_t* bufQ7, uint32_t seed,
                                int length, int16_t AvgPitchGain_Q12) {
   int   k, shft;
   int16_t dither1_Q7, dither2_Q7, dither_gain_Q14;
 
   /* This threshold should be equal to that in decode_spec(). */
@@ skipping 1879 matching lines @@
   /* Use the same CDF table as for bandwidth
    * both take two values with equal probability. */
   if (WebRtcIsac_DecHistOneStepMulti(&intVar, streamData,
                                      kOneBitEqualProbCdf_ptr,
                                      kOneBitEqualProbInitIndex, 1) < 0) {
     return -ISAC_RANGE_ERROR_DECODE_BANDWITH;
   }
   *jitterInfo = (int16_t)(intVar);
   return 0;
 }