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70 lines
2.0 KiB
C++
70 lines
2.0 KiB
C++
// Copyright 2014 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "leb128.h"
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#include <stdint.h>
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#include <vector>
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#include "elf_traits.h"
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namespace relocation_packer {
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// Empty constructor and destructor to silence chromium-style.
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Leb128Encoder::Leb128Encoder() { }
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Leb128Encoder::~Leb128Encoder() { }
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// Add a single value to the encoding. Values are encoded with variable
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// length. The least significant 7 bits of each byte hold 7 bits of data,
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// and the most significant bit is set on each byte except the last.
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void Leb128Encoder::Enqueue(ELF::Xword value) {
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do {
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const uint8_t byte = value & 127;
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value >>= 7;
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encoding_.push_back((value ? 128 : 0) | byte);
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} while (value);
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}
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// Add a vector of values to the encoding.
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void Leb128Encoder::EnqueueAll(const std::vector<ELF::Xword>& values) {
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for (size_t i = 0; i < values.size(); ++i)
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Enqueue(values[i]);
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}
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// Create a new decoder for the given encoded stream.
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Leb128Decoder::Leb128Decoder(const std::vector<uint8_t>& encoding) {
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encoding_ = encoding;
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cursor_ = 0;
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}
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// Empty destructor to silence chromium-style.
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Leb128Decoder::~Leb128Decoder() { }
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// Decode and retrieve a single value from the encoding. Read forwards until
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// a byte without its most significant bit is found, then read the 7 bit
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// fields of the bytes spanned to re-form the value.
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ELF::Xword Leb128Decoder::Dequeue() {
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ELF::Xword value = 0;
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size_t shift = 0;
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uint8_t byte;
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// Loop until we reach a byte with its high order bit clear.
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do {
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byte = encoding_[cursor_++];
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value |= static_cast<ELF::Xword>(byte & 127) << shift;
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shift += 7;
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} while (byte & 128);
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return value;
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}
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// Decode and retrieve all remaining values from the encoding.
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void Leb128Decoder::DequeueAll(std::vector<ELF::Xword>* values) {
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while (cursor_ < encoding_.size())
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values->push_back(Dequeue());
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}
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} // namespace relocation_packer
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