base32.h

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// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#ifndef FLUTTER_FML_BASE32_H_
#define FLUTTER_FML_BASE32_H_
 
#include <string_view>
#include <utility>
 
#include "flutter/fml/logging.h"
 
namespace fml {
 
template <int from_length, int to_length, int buffer_length>
class BitConverter {
 public:
  void Append(int bits) {
    FML_DCHECK(bits >= 0 && bits < (1 << from_length));
    FML_DCHECK(CanAppend());
    lower_free_bits_ -= from_length;
    buffer_ |= (bits << lower_free_bits_);
  }
 
  int Extract() {
    FML_DCHECK(CanExtract());
    int result = Peek();
    buffer_ = (buffer_ << to_length) & kMask;
    lower_free_bits_ += to_length;
    return result;
  }
 
  int Peek() const { return (buffer_ >> (buffer_length - to_length)); }
  int BitsAvailable() const { return buffer_length - lower_free_bits_; }
  bool CanAppend() const { return lower_free_bits_ >= from_length; }
  bool CanExtract() const { return BitsAvailable() >= to_length; }
 
 private:
  static_assert(buffer_length >= 2 * from_length);
  static_assert(buffer_length >= 2 * to_length);
  static_assert(buffer_length < sizeof(int) * 8);
 
  static constexpr int kMask = (1 << buffer_length) - 1;
 
  int buffer_ = 0;
  int lower_free_bits_ = buffer_length;
};
 
using Base32DecodeConverter = BitConverter<5, 8, 16>;
using Base32EncodeConverter = BitConverter<8, 5, 16>;
 
std::pair<bool, std::string> Base32Encode(std::string_view input);
std::pair<bool, std::string> Base32Decode(const std::string& input);
 
}  // namespace fml
 
#endif  // FLUTTER_FML_BASE32_H_