//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.

//  This source code is licensed under both the GPLv2 (found in the

//  COPYING file in the root directory) and Apache 2.0 License

//  (found in the LICENSE.Apache file in the root directory).

//

// 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.

//

// Common hash functions with convenient interfaces. If hashing a

// statically-sized input in a performance-critical context, consider

// calling a specific hash implementation directly, such as

// XXH3_64bits from xxhash.h.

//

// Since this is a very common header, implementation details are kept

// out-of-line. Out-of-lining also aids in tracking the time spent in

// hashing functions. Inlining is of limited benefit for runtime-sized

// hash inputs.

#pragma once

#include <cstddef>

#include <cstdint>

#include "rocksdb/slice.h"

#include "util/fastrange.h"

namespace ROCKSDB_NAMESPACE {

// Stable/persistent 64-bit hash. Higher quality and generally faster than

// Hash(), especially for inputs > 24 bytes.

// KNOWN FLAW: incrementing seed by 1 might not give sufficiently independent

// results from previous seed. Recommend incrementing by a large odd number.

uint64_t Hash64(const char* data, size_t n, uint64_t seed);

// Specific optimization without seed (same as seed = 0)

uint64_t Hash64(const char* data, size_t n);

// Non-persistent hash. Must only used for in-memory data structures.

// The hash results are thus subject to change between releases,

// architectures, build configuration, etc. (Thus, it rarely makes sense

// to specify a seed for this function, except for a "rolling" hash.)

// KNOWN FLAW: incrementing seed by 1 might not give sufficiently independent

// results from previous seed. Recommend incrementing by a large odd number.

inline uint64_t NPHash64(const char* data, size_t n, uint64_t seed) {

#ifdef ROCKSDB_MODIFY_NPHASH

  // For testing "subject to change"

  return Hash64(data, n, seed + 123456789);

#else

  // Currently same as Hash64

  return Hash64(data, n, seed);

#endif

}

// Specific optimization without seed (same as seed = 0)

inline uint64_t NPHash64(const char* data, size_t n) {

#ifdef ROCKSDB_MODIFY_NPHASH

  // For testing "subject to change"

  return Hash64(data, n, 123456789);

#else

  // Currently same as Hash64

  return Hash64(data, n);

#endif

}

// Convenient and equivalent version of Hash128 without depending on 128-bit

// scalars

void Hash2x64(const char* data, size_t n, uint64_t* high64, uint64_t* low64);

void Hash2x64(const char* data, size_t n, uint64_t seed, uint64_t* high64,

              uint64_t* low64);

// Hash 128 bits to 128 bits, guaranteed not to lose data (equivalent to

// Hash2x64 on 16 bytes little endian)

void BijectiveHash2x64(uint64_t in_high64, uint64_t in_low64,

                       uint64_t* out_high64, uint64_t* out_low64);

void BijectiveHash2x64(uint64_t in_high64, uint64_t in_low64, uint64_t seed,

                       uint64_t* out_high64, uint64_t* out_low64);

// Inverse of above (mostly for testing)

void BijectiveUnhash2x64(uint64_t in_high64, uint64_t in_low64,

                         uint64_t* out_high64, uint64_t* out_low64);

void BijectiveUnhash2x64(uint64_t in_high64, uint64_t in_low64, uint64_t seed,

                         uint64_t* out_high64, uint64_t* out_low64);

// Stable/persistent 32-bit hash. Moderate quality and high speed on

// small inputs.

// TODO: consider rename to Hash32

// KNOWN FLAW: incrementing seed by 1 might not give sufficiently independent

// results from previous seed. Recommend pseudorandom or hashed seeds.

uint32_t Hash(const char* data, size_t n, uint32_t seed);

// TODO: consider rename to LegacyBloomHash32

inline uint32_t BloomHash(const Slice& key) {

  return Hash(key.data(), key.size(), 0xbc9f1d34);

}

inline uint64_t GetSliceHash64(const Slice& key) {

  return Hash64(key.data(), key.size());

}

// Provided for convenience for use with template argument deduction, where a

// specific overload needs to be used.

extern uint64_t (*kGetSliceNPHash64UnseededFnPtr)(const Slice&);

inline uint64_t GetSliceNPHash64(const Slice& s) {

  return NPHash64(s.data(), s.size());

}

inline uint64_t GetSliceNPHash64(const Slice& s, uint64_t seed) {

  return NPHash64(s.data(), s.size(), seed);

}

// Similar to `GetSliceNPHash64()` with `seed`, but input comes from

// concatenation of `Slice`s in `data`.

uint64_t GetSlicePartsNPHash64(const SliceParts& data, uint64_t seed);

inline size_t GetSliceRangedNPHash(const Slice& s, size_t range) {

  return FastRange64(NPHash64(s.data(), s.size()), range);

}

// TODO: consider rename to GetSliceHash32

inline uint32_t GetSliceHash(const Slice& s) {

  return Hash(s.data(), s.size(), 397);

}

// Useful for splitting up a 64-bit hash

inline uint32_t Upper32of64(uint64_t v) {

  return static_cast<uint32_t>(v >> 32);

}

inline uint32_t Lower32of64(uint64_t v) { return static_cast<uint32_t>(v); }

// std::hash-like interface.

struct SliceHasher32 {

  uint32_t operator()(const Slice& s) const { return GetSliceHash(s); }

};

struct SliceNPHasher64 {

  uint64_t operator()(const Slice& s, uint64_t seed = 0) const {

    return GetSliceNPHash64(s, seed);

  }

};

}  // namespace ROCKSDB_NAMESPACE