Update from chromium 62675d9fb31fb8cedc40f68e78e8445a74f362e7

tools/relocation_packer/src/sleb128.cc

+// Copyright 2014 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 "sleb128.h"
+
+#include <limits.h>
+#include <stdint.h>
+#include <vector>
+
+#include "elf_traits.h"
+
+namespace relocation_packer {
+
+// Empty constructor and destructor to silence chromium-style.
+Sleb128Encoder::Sleb128Encoder() { }
+Sleb128Encoder::~Sleb128Encoder() { }
+
+// Add a single value to the encoding.  Values are encoded with variable
+// length.  The least significant 7 bits of each byte hold 7 bits of data,
+// and the most significant bit is set on each byte except the last.  The
+// value is sign extended up to a multiple of 7 bits (ensuring that the
+// most significant bit is zero for a positive number and one for a
+// negative number).
+void Sleb128Encoder::Enqueue(ELF::Sxword value) {
+  static const size_t size = CHAR_BIT * sizeof(value);
+
+  bool more = true;
+  const bool negative = value < 0;
+
+  while (more) {
+    uint8_t byte = value & 127;
+    value >>= 7;
+
+    // Sign extend if encoding a -ve value.
+    if (negative)
+      value |= -(static_cast<ELF::Sxword>(1) << (size - 7));
+
+    // The sign bit of byte is second high order bit.
+    const bool sign_bit = byte & 64;
+    if ((value == 0 && !sign_bit) || (value == -1 && sign_bit))
+      more = false;
+    else
+      byte |= 128;
+    encoding_.push_back(byte);
+  }
+}
+
+// Add a vector of values to the encoding.
+void Sleb128Encoder::EnqueueAll(const std::vector<ELF::Sxword>& values) {
+  for (size_t i = 0; i < values.size(); ++i)
+    Enqueue(values[i]);
+}
+
+// Create a new decoder for the given encoded stream.
+Sleb128Decoder::Sleb128Decoder(const std::vector<uint8_t>& encoding) {
+  encoding_ = encoding;
+  cursor_ = 0;
+}
+
+// Empty destructor to silence chromium-style.
+Sleb128Decoder::~Sleb128Decoder() { }
+
+// Decode and retrieve a single value from the encoding.  Consume bytes
+// until one without its most significant bit is found, and re-form the
+// value from the 7 bit fields of the bytes consumed.
+ELF::Sxword Sleb128Decoder::Dequeue() {
+  ELF::Sxword value = 0;
+  static const size_t size = CHAR_BIT * sizeof(value);
+
+  size_t shift = 0;
+  uint8_t byte;
+
+  // Loop until we reach a byte with its high order bit clear.
+  do {
+    byte = encoding_[cursor_++];
+    value |= (static_cast<ELF::Sxword>(byte & 127) << shift);
+    shift += 7;
+  } while (byte & 128);
+
+  // The sign bit is second high order bit of the final byte decoded.
+  // Sign extend if value is -ve and we did not shift all of it.
+  if (shift < size && (byte & 64))
+    value |= -(static_cast<ELF::Sxword>(1) << shift);
+
+  return value;
+}
+
+// Decode and retrieve all remaining values from the encoding.
+void Sleb128Decoder::DequeueAll(std::vector<ELF::Sxword>* values) {
+  while (cursor_ < encoding_.size())
+    values->push_back(Dequeue());
+}
+
+}  // namespace relocation_packer