src/lib/util/hash.cc

// Copyright 2020 The Fuchsia 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 "src/lib/util/hash.h"

#include <farmhash.h>

#include <cstddef>
#include <cstdint>
#include <initializer_list>
#include <string>

namespace cobalt::util {
namespace {

constexpr uint32_t kBytesPerInt64 = 8;
constexpr uint32_t kSingleByteMask = 0xFF;

char GetByte(const uint64_t value, const size_t idx) {
  return static_cast<char>(value >> (kBytesPerInt64 * idx) & kSingleByteMask);
}

std::string LittleEndianBytes(const std::initializer_list<uint64_t> values) {
  std::string bytes(kBytesPerInt64 * values.size(), '\0');
  size_t vi = 0;
  for (const uint64_t value : values) {
    for (size_t i = 0; i < kBytesPerInt64; ++i) {
      bytes[vi + i] = GetByte(value, i);
    }
    vi += kBytesPerInt64;
  }
  return bytes;
}

}  // namespace

std::string FarmhashFingerprint(const std::string &data) {
  const farmhash::uint128_t fingerprint = farmhash::Fingerprint128(data);
  return LittleEndianBytes({
      farmhash::Uint128Low64(fingerprint),
      farmhash::Uint128High64(fingerprint),
  });
}

std::string FarmhashFingerprint64(const std::string &data) {
  return LittleEndianBytes({
      farmhash::Fingerprint64(data),
  });
}

uint64_t Farmhash64(const std::string &data) { return farmhash::Fingerprint64(data); }

}  // namespace cobalt::util