src/algorithms/privacy/rappor.cc

#include "src/algorithms/privacy/rappor.h"

#include <unordered_set>

#include "src/algorithms/random/distributions.h"

namespace cobalt {

std::vector<uint64_t> ApplyRapporNoise(const std::vector<uint64_t>& indices, uint64_t max_index,
                                       double p, SecureBitGeneratorInterface<uint32_t>* gen) {
  if (p == 0.0) {
    return indices;
  }
  std::unordered_set<uint64_t> index_set(indices.begin(), indices.end());
  GeometricDistribution dist(gen, p);
  for (uint64_t index = dist.Sample(); index <= max_index; index += dist.Sample() + 1) {
    if (index_set.count(index) > 0) {
      index_set.erase(index);
    } else {
      index_set.insert(index);
    }
  }
  return std::vector<uint64_t>(index_set.begin(), index_set.end());
}

double DebiasRapporCount(uint64_t raw_count, uint64_t num_contributions, double p) {
  return (static_cast<double>(raw_count) - p * static_cast<double>(num_contributions)) /
         (1.0 - 2 * p);
}

}  // namespace cobalt