root/components/rappor/bloom_filter.cc

DEFINITIONS

1. hash_seed_offset_
2. AddString

// 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 "base/logging.h"

// TODO(holte): we can't include "City.h" due to typedef conflicts.
extern uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed);

namespace rappor {

BloomFilter::BloomFilter(uint32_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::AddString(const std::string& str) {
  for (size_t i = 0; i < hash_function_count_; ++i) {
    // Using CityHash here because we have support for it in Dremel.  Many hash
    // functions, such as MD5, SHA1, or Murmur, would probably also work.
    uint32_t index =
        CityHash64WithSeed(str.data(), str.size(), 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 rappor