PVer4: Verify checksum for downloaded updates

components/safe_browsing_db/v4_rice.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/logging.h"
 #include "base/numerics/safe_math.h"
 #include "base/strings/stringprintf.h"
 #include "components/safe_browsing_db/v4_rice.h"
 
 using ::google::protobuf::RepeatedField;
 using ::google::protobuf::int32;
 
 namespace safe_browsing {
 
 namespace {
 
-const unsigned int kMaxBitIndex = 8 * sizeof(uint32_t);
+const int kBitsPerByte = 8;
+const unsigned int kMaxBitIndex = kBitsPerByte * sizeof(uint32_t);
 
 void GetBytesFromUInt32(uint32_t word, char* bytes) {
   const size_t mask = 0xFF;
   bytes[0] = (char)(word & mask);
   bytes[1] = (char)((word >> 8) & mask);
   bytes[2] = (char)((word >> 16) & mask);
   bytes[3] = (char)((word >> 24) & mask);
 }
 
 }  // namespace
@@ skipping 229 matching lines @@
 
 void V4RiceDecoder::GetBitsFromCurrentWord(unsigned int num_requested_bits,
                                            uint32_t* x) {
   uint32_t mask = 0xFFFFFFFF >> (kMaxBitIndex - num_requested_bits);
   *x = current_word_ & mask;
   current_word_ = current_word_ >> num_requested_bits;
   current_word_bit_index_ += num_requested_bits;
 };
 
 std::string V4RiceDecoder::DebugString() const {
+  // Calculates the total number of bits that we have read from the buffer,
+  // excluding those that have been read into current_word_ but not yet
+  // consumed byt GetNextBits().
+  unsigned bits_read = (data_byte_index_ - sizeof(uint32_t)) * kBitsPerByte +
+                       current_word_bit_index_;
   return base::StringPrintf(
-      "current_word_: %x; data_byte_index_; %x, "
+      "bits_read: %x; current_word_: %x; data_byte_index_; %x, "
       "current_word_bit_index_: %x; rice_parameter_: %x",
-      current_word_, data_byte_index_, current_word_bit_index_,
+      bits_read, current_word_, data_byte_index_, current_word_bit_index_,
       rice_parameter_);
 }
 
 std::ostream& operator<<(std::ostream& os, const V4RiceDecoder& rice_decoder) {
   os << rice_decoder.DebugString();
   return os;
 }
 
 }  // namespace safe_browsing