Fix the issue of undefined-shift in VP8GetBit.

webrtc/modules/video_coding/utility/vp8_header_parser.cc

 /*
  *  Copyright (c) 2015 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.
  */
 #include "webrtc/modules/video_coding/utility/vp8_header_parser.h"
@@ skipping 17 matching lines @@
   if (br->buf_ < br->buf_end_) {
     br->bits_ += 8;
     br->value_ = static_cast<uint32_t>(*br->buf_++) | (br->value_ << 8);
   } else if (!br->eof_) {
     br->value_ <<= 8;
     br->bits_ += 8;
     br->eof_ = 1;
   }
 }
 
-static void VP8LoadNewBytes(VP8BitReader* const br) {
+static bool VP8LoadNewBytes(VP8BitReader* const br) {
   int BITS = 24;
   // Read 'BITS' bits at a time.
   if (br->buf_ + sizeof(uint32_t) <= br->buf_end_) {
     uint32_t bits;
     const uint32_t in_bits = *(const uint32_t*)(br->buf_);
     br->buf_ += BITS >> 3;
 #if defined(WEBRTC_ARCH_BIG_ENDIAN)
     bits = static_cast<uint32_t>(in_bits);
     if (BITS != 8 * sizeof(uint32_t))
       bits >>= (8 * sizeof(uint32_t) - BITS);
 #else
     bits = BSwap32(in_bits);
     bits >>= 32 - BITS;
 #endif
     br->value_ = bits | (br->value_ << BITS);
     br->bits_ += BITS;
   } else {
     VP8LoadFinalBytes(br);
   }
+  if (br->bits_ < 0) {
+    br->eof_ = 1;

[pbos-webrtc, 2016/04/19 23:11:50]

Actually, does this happen from VP8LoadFinalBytes? or how does this happen? is
eof_ already set and we should just check eof_ from VP8GetBit?

[jackychen_, 2016/04/20 00:27:18]

I'm not sure. So to be safe, I put the check here.

+    return false;
+  }
+  return true;
 }
 
 static void VP8InitBitReader(VP8BitReader* const br,
                              const uint8_t* const start,
                              const uint8_t* const end) {
   br->range_ = 255 - 1;
   br->buf_ = start;
   br->buf_end_ = end;
   br->value_ = 0;
   br->bits_ = -8;  // To load the very first 8bits.
   br->eof_ = 0;
   VP8LoadNewBytes(br);
 }
 
 // Read a bit with proba 'prob'.
 static int VP8GetBit(VP8BitReader* const br, int prob) {
   uint8_t range = br->range_;
   if (br->bits_ < 0) {
-    VP8LoadNewBytes(br);
+    if (!VP8LoadNewBytes(br))
+      return 0;
   }
-
   const int pos = br->bits_;
   const uint8_t split = (range * prob) >> 8;
   const uint8_t value = static_cast<uint8_t>(br->value_ >> pos);
   int bit;
   if (value > split) {
     range -= split + 1;
     br->value_ -= static_cast<uint32_t>(split + 1) << pos;
     bit = 1;
   } else {
     range = split;
@@ skipping 106 matching lines @@
     LOG(LS_WARNING) << "Failed to get QP, end of file reached.";
     return false;
   }
   *qp = base_q0;
   return true;
 }
 
 }  // namespace vp8
 
 }  // namespace webrtc