iSAC entropy coder: Avoid signed integer overflow

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 164 matching lines @@
   int16_t dither1_Q7, dither2_Q7, dither_gain_Q14;
 
   /* This threshold should be equal to that in decode_spec(). */
   if (AvgPitchGain_Q12 < 614) {
     for (k = 0; k < length - 2; k += 3) {
       /* New random unsigned int. */
       seed = (seed * 196314165) + 907633515;
 
       /* Fixed-point dither sample between -64 and 64 (Q7). */
       /* dither = seed * 128 / 4294967295 */
-      dither1_Q7 = (int16_t)(((int)seed + 16777216) >> 25);
+      dither1_Q7 = (int16_t)(((int32_t)(seed + 16777216)) >> 25);
 
       /* New random unsigned int. */
       seed = (seed * 196314165) + 907633515;
 
       /* Fixed-point dither sample between -64 and 64. */
-      dither2_Q7 = (int16_t)(((int)seed + 16777216) >> 25);
+      dither2_Q7 = (int16_t)(((int32_t)(seed + 16777216)) >> 25);
 
       shft = (seed >> 25) & 15;
       if (shft < 5) {
         bufQ7[k]   = dither1_Q7;
         bufQ7[k + 1] = dither2_Q7;
         bufQ7[k + 2] = 0;
       } else if (shft < 10) {
         bufQ7[k]   = dither1_Q7;
         bufQ7[k + 1] = 0;
         bufQ7[k + 2] = dither2_Q7;
       } else {
         bufQ7[k]   = 0;
         bufQ7[k + 1] = dither1_Q7;
         bufQ7[k + 2] = dither2_Q7;
       }
     }
   } else {
     dither_gain_Q14 = (int16_t)(22528 - 10 * AvgPitchGain_Q12);
 
     /* Dither on half of the coefficients. */
     for (k = 0; k < length - 1; k += 2) {
       /* New random unsigned int */
       seed = (seed * 196314165) + 907633515;
 
       /* Fixed-point dither sample between -64 and 64. */
-      dither1_Q7 = (int16_t)(((int)seed + 16777216) >> 25);
+      dither1_Q7 = (int16_t)(((int32_t)(seed + 16777216)) >> 25);
 
       /* Dither sample is placed in either even or odd index. */
       shft = (seed >> 25) & 1;     /* Either 0 or 1 */
 
       bufQ7[k + shft] = (((dither_gain_Q14 * dither1_Q7) + 8192) >> 14);
       bufQ7[k + 1 - shft] = 0;
     }
   }
 }
 
@@ skipping 19 matching lines @@
     int16_t* bufQ7,
     uint32_t seed,
     int length) {
   int k;
   for (k = 0; k < length; k++) {
     /* new random unsigned int */
     seed = (seed * 196314165) + 907633515;
 
     /* Fixed-point dither sample between -64 and 64 (Q7). */
     /* bufQ7 = seed * 128 / 4294967295 */
-    bufQ7[k] = (int16_t)(((int)seed + 16777216) >> 25);
+    bufQ7[k] = (int16_t)(((int32_t)(seed + 16777216)) >> 25);
 
     /* Scale by 0.35. */
     bufQ7[k] = (int16_t)WEBRTC_SPL_MUL_16_16_RSFT(bufQ7[k], 2048, 13);
   }
 }
 
 /*
  * Function to decode the complex spectrum from the bit stream
  * returns the total number of bytes in the stream.
  */
@@ skipping 1789 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;
 }