1 /* Copyright 2016 The TensorFlow Authors. All Rights Reserved.
2
3 Licensed under the Apache License, Version 2.0 (the "License");
4 you may not use this file except in compliance with the License.
5 You may obtain a copy of the License at
6
7 http://www.apache.org/licenses/LICENSE-2.0
8
9 Unless required by applicable law or agreed to in writing, software
10 distributed under the License is distributed on an "AS IS" BASIS,
11 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 See the License for the specific language governing permissions and
13 limitations under the License.
14 ==============================================================================*/
15
16 #ifndef TENSORFLOW_CORE_PLATFORM_FINGERPRINT_H_
17 #define TENSORFLOW_CORE_PLATFORM_FINGERPRINT_H_
18
19 #include "tensorflow/core/platform/stringpiece.h"
20 #include "tensorflow/core/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
32 namespace tensorflow {
33
34 struct Fprint128 {
35 uint64 low64;
36 uint64 high64;
37 };
38
39 inline bool operator==(const Fprint128& lhs, const Fprint128& rhs) {
40 return lhs.low64 == rhs.low64 && lhs.high64 == rhs.high64;
41 }
42
43 struct Fprint128Hasher {
operatorFprint128Hasher44 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
50 namespace internal {
51 // Mixes some of the bits that got propagated to the high bits back into the
52 // low bits.
ShiftMix(const uint64 val)53 inline uint64 ShiftMix(const uint64 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.
FingerprintCat64(const uint64 fp1,const uint64 fp2)68 inline uint64 FingerprintCat64(const uint64 fp1, const uint64 fp2) {
69 static const uint64 kMul = 0xc6a4a7935bd1e995ULL;
70 uint64 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.
Fingerprint64(const StringPiece s)80 inline uint64 Fingerprint64(const 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).
Fingerprint32(const StringPiece s)94 inline uint32 Fingerprint32(const 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).
Fingerprint128(const StringPiece s)103 inline Fprint128 Fingerprint128(const 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 tensorflow
115
116 #endif // TENSORFLOW_CORE_PLATFORM_FINGERPRINT_H_
117