| // Copyright 2014 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "components/rappor/bloom_filter.h" |
| |
| #include <stddef.h> |
| |
| #include "base/logging.h" |
| #include "base/numerics/safe_conversions.h" |
| #include "third_party/smhasher/src/City.h" |
| |
| namespace rappor { |
| |
| namespace { |
| |
| uint32_t ComputeHash(const std::string& str, uint32_t seed) { |
| // Using CityHash here because we have support for it in Dremel. Many hash |
| // functions, such as MD5, SHA1, or Murmur, would probably also work. |
| return CityHash64WithSeed(str.data(), str.size(), seed); |
| } |
| |
| } // namespace |
| |
| BloomFilter::BloomFilter(size_t bytes_size, |
| uint32_t hash_function_count, |
| uint32_t hash_seed_offset) |
| : bytes_(bytes_size), |
| hash_function_count_(hash_function_count), |
| hash_seed_offset_(hash_seed_offset) { |
| DCHECK_GT(bytes_size, 0u); |
| } |
| |
| BloomFilter::~BloomFilter() {} |
| |
| void BloomFilter::SetString(const std::string& str) { |
| for (size_t i = 0; i < bytes_.size(); ++i) { |
| bytes_[i] = 0; |
| } |
| for (size_t i = 0; i < hash_function_count_; ++i) { |
| uint32_t index = ComputeHash(str, hash_seed_offset_ + i); |
| // Note that the "bytes" are uint8_t, so they are always 8-bits. |
| uint32_t byte_index = (index / 8) % bytes_.size(); |
| uint32_t bit_index = index % 8; |
| bytes_[byte_index] |= 1 << bit_index; |
| } |
| } |
| |
| namespace internal { |
| |
| uint64_t GetBloomBits(size_t bytes_size, |
| uint32_t hash_function_count, |
| uint32_t hash_seed_offset, |
| const std::string& str) { |
| // Make sure result fits in uint64_t. |
| DCHECK_LE(bytes_size, 8u); |
| uint64_t output = 0; |
| const uint64_t bits_size = base::strict_cast<uint64_t>(bytes_size) * 8; |
| for (size_t i = 0; i < hash_function_count; ++i) { |
| uint64_t index = base::strict_cast<uint64_t>( |
| ComputeHash(str, hash_seed_offset + i)); |
| output |= 1ULL << (index % bits_size); |
| } |
| return output; |
| } |
| |
| } // namespace internal |
| |
| } // namespace rappor |