1 files changed, 229 insertions, 0 deletions
diff --git a/toolkit/components/url-classifier/RiceDeltaDecoder.cpp b/toolkit/components/url-classifier/RiceDeltaDecoder.cpp
new file mode 100644
index 000000000..66b0b3d6d
--- /dev/null
+++ b/toolkit/components/url-classifier/RiceDeltaDecoder.cpp
@@ -0,0 +1,229 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RiceDeltaDecoder.h"
+
+namespace {
+
+////////////////////////////////////////////////////////////////////////
+// BitBuffer is copied and modified from webrtc/base/bitbuffer.h
+//
+
+/*
+ *  Copyright 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 (webrtc/base/bitbuffer.h/cc). 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.
+ */
+
+class BitBuffer {
+ public:
+  BitBuffer(const uint8_t* bytes, size_t byte_count);
+
+  // The remaining bits in the byte buffer.
+  uint64_t RemainingBitCount() const;
+
+  // Reads bit-sized values from the buffer. Returns false if there isn't enough
+  // data left for the specified bit count..
+  bool ReadBits(uint32_t* val, size_t bit_count);
+
+  // Peeks bit-sized values from the buffer. Returns false if there isn't enough
+  // data left for the specified number of bits. Doesn't move the current
+  // offset.
+  bool PeekBits(uint32_t* val, size_t bit_count);
+
+  // Reads the exponential golomb encoded value at the current offset.
+  // Exponential golomb values are encoded as:
+  // 1) x = source val + 1
+  // 2) In binary, write [countbits(x) - 1] 1s, then x
+  // To decode, we count the number of leading 1 bits, read that many + 1 bits,
+  // and increment the result by 1.
+  // Returns false if there isn't enough data left for the specified type, or if
+  // the value wouldn't fit in a uint32_t.
+  bool ReadExponentialGolomb(uint32_t* val);
+
+  // Moves current position |bit_count| bits forward. Returns false if
+  // there aren't enough bits left in the buffer.
+  bool ConsumeBits(size_t bit_count);
+
+ protected:
+  const uint8_t* const bytes_;
+  // The total size of |bytes_|.
+  size_t byte_count_;
+  // The current offset, in bytes, from the start of |bytes_|.
+  size_t byte_offset_;
+  // The current offset, in bits, into the current byte.
+  size_t bit_offset_;
+};
+
+} // end of unnamed namespace
+
+static void
+ReverseByte(uint8_t& b)
+{
+  b = (b & 0xF0) >> 4 | (b & 0x0F) << 4;
+  b = (b & 0xCC) >> 2 | (b & 0x33) << 2;
+  b = (b & 0xAA) >> 1 | (b & 0x55) << 1;
+}
+
+namespace mozilla {
+namespace safebrowsing {
+
+RiceDeltaDecoder::RiceDeltaDecoder(uint8_t* aEncodedData,
+                                   size_t aEncodedDataSize)
+  : mEncodedData(aEncodedData)
+  , mEncodedDataSize(aEncodedDataSize)
+{
+}
+
+bool
+RiceDeltaDecoder::Decode(uint32_t aRiceParameter,
+                         uint32_t aFirstValue,
+                         uint32_t aNumEntries,
+                         uint32_t* aDecodedData)
+{
+  // Reverse each byte before reading bits from the byte buffer.
+  for (size_t i = 0; i < mEncodedDataSize; i++) {
+    ReverseByte(mEncodedData[i]);
+  }
+
+  BitBuffer bitBuffer(mEncodedData, mEncodedDataSize);
+
+  // q = quotient
+  // r = remainder
+  // k = RICE parameter
+  const uint32_t k = aRiceParameter;
+  aDecodedData[0] = aFirstValue;
+  for (uint32_t i = 0; i < aNumEntries; i++) {
+    // Read the quotient of N.
+    uint32_t q;
+    if (!bitBuffer.ReadExponentialGolomb(&q)) {
+      LOG(("Encoded data underflow!"));
+      return false;
+    }
+
+    // Read the remainder of N, one bit at a time.
+    uint32_t r = 0;
+    for (uint32_t j = 0; j < k; j++) {
+      uint32_t b = 0;
+      if (!bitBuffer.ReadBits(&b, 1)) {
+        // Insufficient bits. Just leave them as zeros.
+        break;
+      }
+      // Add the bit to the right position so that it's in Little Endian order.
+      r |= b << j;
+    }
+
+    // Caculate N from q,r,k.
+    uint32_t N = (q << k) + r;
+
+    // We start filling aDecodedData from [1].
+    aDecodedData[i + 1] = N + aDecodedData[i];
+  }
+
+  return true;
+}
+
+} // end of namespace mozilla
+} // end of namespace safebrowsing
+
+namespace {
+//////////////////////////////////////////////////////////////////////////
+// The BitBuffer impl is copied and modified from webrtc/base/bitbuffer.cc
+//
+
+// Returns the lowest (right-most) |bit_count| bits in |byte|.
+uint8_t LowestBits(uint8_t byte, size_t bit_count) {
+  return byte & ((1 << bit_count) - 1);
+}
+
+// Returns the highest (left-most) |bit_count| bits in |byte|, shifted to the
+// lowest bits (to the right).
+uint8_t HighestBits(uint8_t byte, size_t bit_count) {
+  MOZ_ASSERT(bit_count < 8u);
+  uint8_t shift = 8 - static_cast<uint8_t>(bit_count);
+  uint8_t mask = 0xFF << shift;
+  return (byte & mask) >> shift;
+}
+
+BitBuffer::BitBuffer(const uint8_t* bytes, size_t byte_count)
+    : bytes_(bytes), byte_count_(byte_count), byte_offset_(), bit_offset_() {
+  MOZ_ASSERT(static_cast<uint64_t>(byte_count_) <=
+             std::numeric_limits<uint32_t>::max());
+}
+
+uint64_t BitBuffer::RemainingBitCount() const {
+  return (static_cast<uint64_t>(byte_count_) - byte_offset_) * 8 - bit_offset_;
+}
+
+bool BitBuffer::PeekBits(uint32_t* val, size_t bit_count) {
+  if (!val || bit_count > RemainingBitCount() || bit_count > 32) {
+    return false;
+  }
+  const uint8_t* bytes = bytes_ + byte_offset_;
+  size_t remaining_bits_in_current_byte = 8 - bit_offset_;
+  uint32_t bits = LowestBits(*bytes++, remaining_bits_in_current_byte);
+  // If we're reading fewer bits than what's left in the current byte, just
+  // return the portion of this byte that we need.
+  if (bit_count < remaining_bits_in_current_byte) {
+    *val = HighestBits(bits, bit_offset_ + bit_count);
+    return true;
+  }
+  // Otherwise, subtract what we've read from the bit count and read as many
+  // full bytes as we can into bits.
+  bit_count -= remaining_bits_in_current_byte;
+  while (bit_count >= 8) {
+    bits = (bits << 8) | *bytes++;
+    bit_count -= 8;
+  }
+  // Whatever we have left is smaller than a byte, so grab just the bits we need
+  // and shift them into the lowest bits.
+  if (bit_count > 0) {
+    bits <<= bit_count;
+    bits |= HighestBits(*bytes, bit_count);
+  }
+  *val = bits;
+  return true;
+}
+
+bool BitBuffer::ReadBits(uint32_t* val, size_t bit_count) {
+  return PeekBits(val, bit_count) && ConsumeBits(bit_count);
+}
+
+bool BitBuffer::ConsumeBits(size_t bit_count) {
+  if (bit_count > RemainingBitCount()) {
+    return false;
+  }
+
+  byte_offset_ += (bit_offset_ + bit_count) / 8;
+  bit_offset_ = (bit_offset_ + bit_count) % 8;
+  return true;
+}
+
+bool BitBuffer::ReadExponentialGolomb(uint32_t* val) {
+  if (!val) {
+    return false;
+  }
+
+  *val = 0;
+
+  // Count the number of leading 0 bits by peeking/consuming them one at a time.
+  size_t one_bit_count = 0;
+  uint32_t peeked_bit;
+  while (PeekBits(&peeked_bit, 1) && peeked_bit == 1) {
+    one_bit_count++;
+    ConsumeBits(1);
+  }
+  if (!ConsumeBits(1)) {
+    return false; // The stream is incorrectly terminated at '1'.
+  }
+
+  *val = one_bit_count;
+  return true;
+}
+}