1/* Copyright 2016 The TensorFlow Authors. All Rights Reserved.
2
3Licensed under the Apache License, Version 2.0 (the "License");
4you may not use this file except in compliance with the License.
5You may obtain a copy of the License at
6
7 http://www.apache.org/licenses/LICENSE-2.0
8
9Unless required by applicable law or agreed to in writing, software
10distributed under the License is distributed on an "AS IS" BASIS,
11WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12See the License for the specific language governing permissions and
13limitations under the License.
14==============================================================================*/
15
16#ifndef TENSORFLOW_TSL_PLATFORM_FINGERPRINT_H_
17#define TENSORFLOW_TSL_PLATFORM_FINGERPRINT_H_
18
19#include "tensorflow/tsl/platform/stringpiece.h"
20#include "tensorflow/tsl/platform/types.h"
21
22// The following line is used by copybara to set or unset the USE_OSS_FARMHASH
23// preprocessor symbol as needed. Please do not remove.
24#define USE_OSS_FARMHASH
25
26#ifdef USE_OSS_FARMHASH
27#include <farmhash.h>
28#else
29#include "util/hash/farmhash_fingerprint.h"
30#endif
31
32namespace tsl {
33
34struct Fprint128 {
35 uint64_t low64;
36 uint64_t high64;
37};
38
39inline bool operator==(const Fprint128& lhs, const Fprint128& rhs) {
40 return lhs.low64 == rhs.low64 && lhs.high64 == rhs.high64;
41}
42
43struct Fprint128Hasher {
44 size_t operator()(const Fprint128& v) const {
45 // Low64 should be sufficiently mixed to allow use of it as a Hash.
46 return static_cast<size_t>(v.low64);
47 }
48};
49
50namespace internal {
51// Mixes some of the bits that got propagated to the high bits back into the
52// low bits.
53inline uint64_t ShiftMix(const uint64_t val) { return val ^ (val >> 47); }
54} // namespace internal
55
56// This concatenates two 64-bit fingerprints. It is a convenience function to
57// get a fingerprint for a combination of already fingerprinted components. For
58// example this code is used to concatenate the hashes from each of the features
59// on sparse crosses.
60//
61// One shouldn't expect FingerprintCat64(Fingerprint64(x), Fingerprint64(y))
62// to indicate anything about FingerprintCat64(StrCat(x, y)). This operation
63// is not commutative.
64//
65// From a security standpoint, we don't encourage this pattern to be used
66// for everything as it is vulnerable to length-extension attacks and it
67// is easier to compute multicollisions.
68inline uint64_t FingerprintCat64(const uint64_t fp1, const uint64_t fp2) {
69 static const uint64_t kMul = 0xc6a4a7935bd1e995ULL;
70 uint64_t result = fp1 ^ kMul;
71 result ^= internal::ShiftMix(fp2 * kMul) * kMul;
72 result *= kMul;
73 result = internal::ShiftMix(result) * kMul;
74 result = internal::ShiftMix(result);
75 return result;
76}
77
78// This is a portable fingerprint interface for strings that will never change.
79// However, it is not suitable for cryptography.
80inline uint64_t Fingerprint64(const tsl::StringPiece s) {
81#ifdef USE_OSS_FARMHASH
82 return ::util::Fingerprint64(s.data(), s.size());
83#else
84 // Fingerprint op depends on the fact that Fingerprint64() is implemented by
85 // Farmhash. If the implementation ever changes, Fingerprint op should be
86 // modified to keep using Farmhash.
87 // LINT.IfChange
88 return farmhash::Fingerprint64(s.data(), s.size());
89 // LINT.ThenChange(//third_party/tensorflow/core/kernels/fingerprint_op.cc)
90#endif
91}
92
93// 32-bit variant of Fingerprint64 above (same properties and caveats apply).
94inline uint32_t Fingerprint32(const tsl::StringPiece s) {
95#ifdef USE_OSS_FARMHASH
96 return ::util::Fingerprint32(s.data(), s.size());
97#else
98 return farmhash::Fingerprint32(s.data(), s.size());
99#endif
100}
101
102// 128-bit variant of Fingerprint64 above (same properties and caveats apply).
103inline Fprint128 Fingerprint128(const tsl::StringPiece s) {
104#ifdef USE_OSS_FARMHASH
105 const auto fingerprint = ::util::Fingerprint128(s.data(), s.size());
106 return {::util::Uint128Low64(fingerprint),
107 ::util::Uint128High64(fingerprint)};
108#else
109 const auto fingerprint = farmhash::Fingerprint128(s.data(), s.size());
110 return {absl::Uint128Low64(fingerprint), absl::Uint128High64(fingerprint)};
111#endif
112}
113
114} // namespace tsl
115
116#endif // TENSORFLOW_TSL_PLATFORM_FINGERPRINT_H_
117