// Copyright (c) 2011 The LevelDB Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file. See the AUTHORS file for names of contributors.

//

// Endian-neutral encoding:

// * Fixed-length numbers are encoded with least-significant byte first

// * In addition we support variable length "varint" encoding

// * Strings are encoded prefixed by their length in varint format

#ifndef STORAGE_LEVELDB_UTIL_CODING_H_

#define STORAGE_LEVELDB_UTIL_CODING_H_

#include <cstdint>

#include <cstring>

#include <string>

#include "leveldb/slice.h"

#include "port/port.h"

namespace leveldb {

// Standard Put... routines append to a string

void PutFixed32(std::string* dst, uint32_t value);

void PutFixed64(std::string* dst, uint64_t value);

void PutVarint32(std::string* dst, uint32_t value);

void PutVarint64(std::string* dst, uint64_t value);

void PutLengthPrefixedSlice(std::string* dst, const Slice& value);

// Standard Get... routines parse a value from the beginning of a Slice

// and advance the slice past the parsed value.

bool GetVarint32(Slice* input, uint32_t* value);

bool GetVarint64(Slice* input, uint64_t* value);

bool GetLengthPrefixedSlice(Slice* input, Slice* result);

// Pointer-based variants of GetVarint...  These either store a value

// in *v and return a pointer just past the parsed value, or return

// nullptr on error.  These routines only look at bytes in the range

// [p..limit-1]

const char* GetVarint32Ptr(const char* p, const char* limit, uint32_t* v);

const char* GetVarint64Ptr(const char* p, const char* limit, uint64_t* v);

// Returns the length of the varint32 or varint64 encoding of "v"

int VarintLength(uint64_t v);

// Lower-level versions of Put... that write directly into a character buffer

// and return a pointer just past the last byte written.

// REQUIRES: dst has enough space for the value being written

char* EncodeVarint32(char* dst, uint32_t value);

char* EncodeVarint64(char* dst, uint64_t value);

// Lower-level versions of Put... that write directly into a character buffer

// REQUIRES: dst has enough space for the value being written

inline void EncodeFixed32(char* dst, uint32_t value) {

  uint8_t* const buffer = reinterpret_cast<uint8_t*>(dst);

  // Recent clang and gcc optimize this to a single mov / str instruction.

  buffer[0] = static_cast<uint8_t>(value);

  buffer[1] = static_cast<uint8_t>(value >> 8);

  buffer[2] = static_cast<uint8_t>(value >> 16);

  buffer[3] = static_cast<uint8_t>(value >> 24);

}

inline void EncodeFixed64(char* dst, uint64_t value) {

  uint8_t* const buffer = reinterpret_cast<uint8_t*>(dst);

  // Recent clang and gcc optimize this to a single mov / str instruction.

  buffer[0] = static_cast<uint8_t>(value);

  buffer[1] = static_cast<uint8_t>(value >> 8);

  buffer[2] = static_cast<uint8_t>(value >> 16);

  buffer[3] = static_cast<uint8_t>(value >> 24);

  buffer[4] = static_cast<uint8_t>(value >> 32);

  buffer[5] = static_cast<uint8_t>(value >> 40);

  buffer[6] = static_cast<uint8_t>(value >> 48);

  buffer[7] = static_cast<uint8_t>(value >> 56);

}

// Lower-level versions of Get... that read directly from a character buffer

// without any bounds checking.

inline uint32_t DecodeFixed32(const char* ptr) {

  const uint8_t* const buffer = reinterpret_cast<const uint8_t*>(ptr);

  // Recent clang and gcc optimize this to a single mov / ldr instruction.

  return (static_cast<uint32_t>(buffer[0])) |

         (static_cast<uint32_t>(buffer[1]) << 8) |

         (static_cast<uint32_t>(buffer[2]) << 16) |

         (static_cast<uint32_t>(buffer[3]) << 24);

}

inline uint64_t DecodeFixed64(const char* ptr) {

  const uint8_t* const buffer = reinterpret_cast<const uint8_t*>(ptr);

  // Recent clang and gcc optimize this to a single mov / ldr instruction.

  return (static_cast<uint64_t>(buffer[0])) |

         (static_cast<uint64_t>(buffer[1]) << 8) |

         (static_cast<uint64_t>(buffer[2]) << 16) |

         (static_cast<uint64_t>(buffer[3]) << 24) |

         (static_cast<uint64_t>(buffer[4]) << 32) |

         (static_cast<uint64_t>(buffer[5]) << 40) |

         (static_cast<uint64_t>(buffer[6]) << 48) |

         (static_cast<uint64_t>(buffer[7]) << 56);

}

// Internal routine for use by fallback path of GetVarint32Ptr

const char* GetVarint32PtrFallback(const char* p, const char* limit,

                                   uint32_t* value);

inline const char* GetVarint32Ptr(const char* p, const char* limit,

                                  uint32_t* value) {

  if (p < limit) {

    uint32_t result = *(reinterpret_cast<const uint8_t*>(p));

    if ((result & 128) == 0) {

      *value = result;

      return p + 1;

    }

  }

  return GetVarint32PtrFallback(p, limit, value);

}

}  // namespace leveldb

#endif  // STORAGE_LEVELDB_UTIL_CODING_H_