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milaGGLmilaGGL
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Implement BloomFilter class (#10846)
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+325
-7
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4 files changed

+325
-7
lines changed

‎Firestore/Example/Firestore.xcodeproj/project.pbxproj‎

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1082+
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1290+
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‎Firestore/core/src/remote/bloom_filter.cc‎

Lines changed: 127 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,127 @@
1+
/*
2+
* Copyright 2023 Google LLC
3+
*
4+
* Licensed under the Apache License, Version 2.0 (the "License");
5+
* you may not use this file except in compliance with the License.
6+
* You may obtain a copy of the License at
7+
*
8+
* http://www.apache.org/licenses/LICENSE-2.0
9+
*
10+
* Unless required by applicable law or agreed to in writing, software
11+
* distributed under the License is distributed on an "AS IS" BASIS,
12+
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13+
* See the License for the specific language governing permissions and
14+
* limitations under the License.
15+
*/
16+
17+
#include "Firestore/core/src/remote/bloom_filter.h"
18+
19+
#include <utility>
20+
21+
#include "CommonCrypto/CommonDigest.h"
22+
#include "Firestore/core/src/util/hard_assert.h"
23+
#include "Firestore/core/src/util/statusor.h"
24+
#include "Firestore/core/src/util/warnings.h"
25+
26+
namespace firebase {
27+
namespace firestore {
28+
namespace remote {
29+
30+
using util::Status;
31+
using util::StatusOr;
32+
33+
// TODO(Mila): Replace CommonCrypto with platform based MD5 calculation and
34+
// remove suppress.
35+
SUPPRESS_DEPRECATED_DECLARATIONS_BEGIN();
36+
37+
BloomFilter::Hash BloomFilter::Md5HashDigest(absl::string_view key) const {
38+
unsigned char md5_digest[CC_MD5_DIGEST_LENGTH];
39+
40+
CC_MD5_CTX context;
41+
CC_MD5_Init(&context);
42+
CC_MD5_Update(&context, key.data(), key.size());
43+
CC_MD5_Final(md5_digest, &context);
44+
45+
// TODO(Mila): Replace this casting with safer function (b/270568625).
46+
uint64_t* hash128 = reinterpret_cast<uint64_t*>(md5_digest);
47+
return Hash{hash128[0], hash128[1]};
48+
}
49+
SUPPRESS_END();
50+
51+
int32_t BloomFilter::GetBitIndex(const Hash& hash, int32_t hash_index) const {
52+
HARD_ASSERT(hash_index >= 0);
53+
uint64_t hash_index_uint64 = static_cast<uint64_t>(hash_index);
54+
uint64_t bit_count_uint64 = static_cast<uint64_t>(bit_count_);
55+
56+
uint64_t combined_hash = hash.h1 + (hash_index_uint64 * hash.h2);
57+
uint64_t bit_index = combined_hash % bit_count_uint64;
58+
59+
HARD_ASSERT(bit_index <= INT32_MAX);
60+
return bit_index;
61+
}
62+
63+
bool BloomFilter::IsBitSet(int32_t index) const {
64+
uint8_t byte_at_index = bitmap_[index / 8];
65+
int32_t offset = index % 8;
66+
return (byte_at_index & (static_cast<uint8_t>(0x01) << offset)) != 0;
67+
}
68+
69+
BloomFilter::BloomFilter(std::vector<uint8_t> bitmap,
70+
int32_t padding,
71+
int32_t hash_count)
72+
: bit_count_(static_cast<int32_t>(bitmap.size()) * 8 - padding),
73+
hash_count_(hash_count),
74+
bitmap_(std::move(bitmap)) {
75+
HARD_ASSERT(padding >= 0 && padding < 8);
76+
HARD_ASSERT(hash_count_ >= 0);
77+
// Only empty bloom filter can have 0 hash count.
78+
HARD_ASSERT(bitmap_.size() == 0 || hash_count_ != 0);
79+
// Empty bloom filter should have 0 padding.
80+
HARD_ASSERT(bitmap_.size() != 0 || padding == 0);
81+
HARD_ASSERT(bit_count_ >= 0);
82+
}
83+
84+
StatusOr<BloomFilter> BloomFilter::Create(std::vector<uint8_t> bitmap,
85+
int32_t padding,
86+
int32_t hash_count) {
87+
if (padding < 0 || padding >= 8) {
88+
return Status(firestore::Error::kErrorInvalidArgument,
89+
"Invalid padding: " + std::to_string(padding));
90+
}
91+
if (hash_count < 0) {
92+
return Status(firestore::Error::kErrorInvalidArgument,
93+
"Invalid hash count: " + std::to_string(hash_count));
94+
}
95+
if (bitmap.size() > 0 && hash_count == 0) {
96+
// Only empty bloom filter can have 0 hash count.
97+
return Status(firestore::Error::kErrorInvalidArgument,
98+
"Invalid hash count: " + std::to_string(hash_count));
99+
}
100+
if (bitmap.size() == 0 && padding != 0) {
101+
// Empty bloom filter should have 0 padding.
102+
return Status(firestore::Error::kErrorInvalidArgument,
103+
"Expected padding of 0 when bitmap length is 0, but got " +
104+
std::to_string(padding));
105+
}
106+
107+
return BloomFilter(std::move(bitmap), padding, hash_count);
108+
}
109+
110+
bool BloomFilter::MightContain(absl::string_view value) const {
111+
// Empty bitmap should return false on membership check.
112+
if (bit_count_ == 0) return false;
113+
Hash hash = Md5HashDigest(value);
114+
// The `hash_count_` and `bit_count_` fields are guaranteed to be
115+
// non-negative when the `BloomFilter` object is constructed.
116+
for (int32_t i = 0; i < hash_count_; ++i) {
117+
int32_t index = GetBitIndex(hash, i);
118+
if (!IsBitSet(index)) {
119+
return false;
120+
}
121+
}
122+
return true;
123+
}
124+
125+
} // namespace remote
126+
} // namespace firestore
127+
} // namespace firebase

‎Firestore/core/src/remote/bloom_filter.h‎

Lines changed: 46 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -19,6 +19,7 @@
1919

2020
#include <string>
2121
#include <vector>
22+
#include "Firestore/core/src/util/statusor.h"
2223
#include "absl/strings/string_view.h"
2324

2425
namespace firebase {
@@ -35,6 +36,16 @@ class BloomFilter final {
3536
BloomFilter& operator=(const BloomFilter&) = default;
3637
BloomFilter& operator=(BloomFilter&&) = default;
3738

39+
/**
40+
* Creates a BloomFilter object or returns a status.
41+
*
42+
* @return a new BloomFilter if the inputs are valid, otherwise returns a not
43+
* `ok()` status.
44+
*/
45+
static util::StatusOr<BloomFilter> Create(std::vector<uint8_t> bitmap,
46+
int32_t padding,
47+
int32_t hash_count);
48+
3849
/**
3950
* Check whether the given string is a possible member of the bloom filter. It
4051
* might return false positive result, ie, the given string is not a member of
@@ -46,22 +57,50 @@ class BloomFilter final {
4657
*/
4758
bool MightContain(absl::string_view value) const;
4859

49-
// Get the `bit_count_` field. Used for testing purpose.
60+
/** Get the `bit_count_` field. Used for testing purpose. */
5061
int32_t bit_count() const {
5162
return bit_count_;
5263
}
5364

5465
private:
55-
// The number of bits in the bloom filter. Guaranteed to be non-negative, and
56-
// less than the max number of bits `bitmap_` can represent, i.e.,
57-
// bitmap_.size() * 8.
66+
/**
67+
* When checking membership of a key in bitmap, the first step is to generate
68+
* a 128-bit hash, and treat it as 2 distinct 64-bit hash values, named `h1`
69+
* and `h2`, interpreted as unsigned integers using 2's complement encoding.
70+
*/
71+
struct Hash {
72+
uint64_t h1;
73+
uint64_t h2;
74+
};
75+
76+
/**
77+
* Calculate the MD5 digest of the given string, and return a Hash object.
78+
*/
79+
Hash Md5HashDigest(absl::string_view key) const;
80+
81+
/**
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* Calculate the ith hash value based on the hashed 64 bit unsigned integers,
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* and calculate its corresponding bit index in the bitmap to be checked.
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*/
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int32_t GetBitIndex(const Hash& hash, int32_t hash_index) const;
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/** Return whether the bit at the given index in the bitmap is set to 1. */
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bool IsBitSet(int32_t index) const;
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/**
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* The number of bits in the bloom filter. Guaranteed to be non-negative, and
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* less than the max number of bits `bitmap_` can represent, i.e.,
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* bitmap_.size() * 8.
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*/
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int32_t bit_count_ = 0;
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60-
// The number of hash functions used to construct the filter. Guaranteed to be
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// non-negative.
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/**
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* The number of hash functions used to construct the filter. Guaranteed to
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* be non-negative.
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*/
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int32_t hash_count_ = 0;
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64-
// Bloom filter's bitmap.
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/** Bloom filter's bitmap. */
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std::vector<uint8_t> bitmap_;
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};
67106

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