Fix "left shift of negative value" bug

webrtc/common_audio/signal_processing/filter_ar.c

 /*
  *  Copyright (c) 2011 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 27 matching lines @@
 
     for (i = 0; i < x_length; i++)
     {
         // Calculate filtered[i] and filtered_low[i]
         const int16_t* a_ptr = &a[1];
         int16_t* filtered_ptr = &filtered[i - 1];
         int16_t* filtered_low_ptr = &filtered_low[i - 1];
         int16_t* state_ptr = &state[state_length - 1];
         int16_t* state_low_ptr = &state_low[state_length - 1];
 
-        o = (int32_t)(*x_ptr++) << 12;
+        o = (int32_t)(*x_ptr++) * (1 << 12);
         oLOW = (int32_t)0;
 
         stop = (i < a_length) ? i + 1 : a_length;
         for (j = 1; j < stop; j++)
         {
           o -= *a_ptr * *filtered_ptr--;
           oLOW -= *a_ptr++ * *filtered_low_ptr--;
         }
         for (j = i + 1; j < a_length; j++)
         {
           o -= *a_ptr * *state_ptr--;
           oLOW -= *a_ptr++ * *state_low_ptr--;
         }
 
         o += (oLOW >> 12);
         *filteredFINAL_ptr = (int16_t)((o + (int32_t)2048) >> 12);
-        *filteredFINAL_LOW_ptr++ = (int16_t)(o - ((int32_t)(*filteredFINAL_ptr++)
-                << 12));
+        *filteredFINAL_LOW_ptr++ =
+            (int16_t)(o - ((int32_t)(*filteredFINAL_ptr++) * (1 << 12)));
     }
 
     // Save the filter state
     if (x_length >= state_length)
     {
         WebRtcSpl_CopyFromEndW16(filtered, x_length, a_length - 1, state);
         WebRtcSpl_CopyFromEndW16(filtered_low, x_length, a_length - 1, state_low);
     } else
     {
         for (i = 0; i < state_length - x_length; i++)
         {
             state[i] = state[i + x_length];
             state_low[i] = state_low[i + x_length];
         }
         for (i = 0; i < x_length; i++)
         {
             state[state_length - x_length + i] = filtered[i];
             state[state_length - x_length + i] = filtered_low[i];
         }
     }
 
     return x_length;
 }