robin_growth_policy.h

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#ifndef TSL_ROBIN_GROWTH_POLICY_H
#define TSL_ROBIN_GROWTH_POLICY_H
 
#include <algorithm>
#include <array>
#include <climits>
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <limits>
#include <ratio>
#include <stdexcept>
 
// A change of the major version indicates an API and/or ABI break (change of
// in-memory layout of the data structure)
#define TSL_RH_VERSION_MAJOR 1
// A change of the minor version indicates the addition of a feature without
// impact on the API/ABI
#define TSL_RH_VERSION_MINOR 3
// A change of the patch version indicates a bugfix without additional
// functionality
#define TSL_RH_VERSION_PATCH 0
 
#ifdef TSL_DEBUG
#define tsl_rh_assert(expr) assert(expr)
#else
#define tsl_rh_assert(expr) (static_cast<void>(0))
#endif
 
#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || \
     (defined(_MSC_VER) && defined(_CPPUNWIND))) &&        \
    !defined(TSL_NO_EXCEPTIONS)
#define TSL_RH_THROW_OR_TERMINATE(ex, msg) throw ex(msg)
#else
#define TSL_RH_NO_EXCEPTIONS
#ifdef TSL_DEBUG
#include <iostream>
#define TSL_RH_THROW_OR_TERMINATE(ex, msg) \
  do {                                     \
    std::cerr << msg << std::endl;         \
    std::terminate();                      \
  } while (0)
#else
#define TSL_RH_THROW_OR_TERMINATE(ex, msg) std::terminate()
#endif
#endif
 
#if defined(__GNUC__) || defined(__clang__)
#define TSL_RH_LIKELY(exp) (__builtin_expect(!!(exp), true))
#else
#define TSL_RH_LIKELY(exp) (exp)
#endif
 
#define TSL_RH_UNUSED(x) static_cast<void>(x)
 
namespace tsl {
namespace rh {
 
template <std::size_t GrowthFactor>
class power_of_two_growth_policy {
 public:
  explicit power_of_two_growth_policy(std::size_t& min_bucket_count_in_out) {
    if (min_bucket_count_in_out > max_bucket_count()) {
      TSL_RH_THROW_OR_TERMINATE(std::length_error,
                                "The hash table exceeds its maximum size.");
    }
 
    if (min_bucket_count_in_out > 0) {
      min_bucket_count_in_out =
          round_up_to_power_of_two(min_bucket_count_in_out);
      m_mask = min_bucket_count_in_out - 1;
    } else {
      m_mask = 0;
    }
  }
 
  std::size_t bucket_for_hash(std::size_t hash) const noexcept {
    return hash & m_mask;
  }
 
  std::size_t next_bucket_count() const {
    if ((m_mask + 1) > max_bucket_count() / GrowthFactor) {
      TSL_RH_THROW_OR_TERMINATE(std::length_error,
                                "The hash table exceeds its maximum size.");
    }
 
    return (m_mask + 1) * GrowthFactor;
  }
 
  std::size_t max_bucket_count() const {
    // Largest power of two.
    return (std::numeric_limits<std::size_t>::max() / 2) + 1;
  }
 
  void clear() noexcept { m_mask = 0; }
 
 private:
  static std::size_t round_up_to_power_of_two(std::size_t value) {
    if (is_power_of_two(value)) {
      return value;
    }
 
    if (value == 0) {
      return 1;
    }
 
    --value;
    for (std::size_t i = 1; i < sizeof(std::size_t) * CHAR_BIT; i *= 2) {
      value |= value >> i;
    }
 
    return value + 1;
  }
 
  static constexpr bool is_power_of_two(std::size_t value) {
    return value != 0 && (value & (value - 1)) == 0;
  }
 
 protected:
  static_assert(is_power_of_two(GrowthFactor) && GrowthFactor >= 2,
                "GrowthFactor must be a power of two >= 2.");
 
  std::size_t m_mask;
};
 
template <class GrowthFactor = std::ratio<3, 2>>
class mod_growth_policy {
 public:
  explicit mod_growth_policy(std::size_t& min_bucket_count_in_out) {
    if (min_bucket_count_in_out > max_bucket_count()) {
      TSL_RH_THROW_OR_TERMINATE(std::length_error,
                                "The hash table exceeds its maximum size.");
    }
 
    if (min_bucket_count_in_out > 0) {
      m_mod = min_bucket_count_in_out;
    } else {
      m_mod = 1;
    }
  }
 
  std::size_t bucket_for_hash(std::size_t hash) const noexcept {
    return hash % m_mod;
  }
 
  std::size_t next_bucket_count() const {
    if (m_mod == max_bucket_count()) {
      TSL_RH_THROW_OR_TERMINATE(std::length_error,
                                "The hash table exceeds its maximum size.");
    }
 
    const double next_bucket_count =
        std::ceil(double(m_mod) * REHASH_SIZE_MULTIPLICATION_FACTOR);
    if (!std::isnormal(next_bucket_count)) {
      TSL_RH_THROW_OR_TERMINATE(std::length_error,
                                "The hash table exceeds its maximum size.");
    }
 
    if (next_bucket_count > double(max_bucket_count())) {
      return max_bucket_count();
    } else {
      return std::size_t(next_bucket_count);
    }
  }
 
  std::size_t max_bucket_count() const { return MAX_BUCKET_COUNT; }
 
  void clear() noexcept { m_mod = 1; }
 
 private:
  static constexpr double REHASH_SIZE_MULTIPLICATION_FACTOR =
      1.0 * GrowthFactor::num / GrowthFactor::den;
  static const std::size_t MAX_BUCKET_COUNT =
      std::size_t(double(std::numeric_limits<std::size_t>::max() /
                         REHASH_SIZE_MULTIPLICATION_FACTOR));
 
  static_assert(REHASH_SIZE_MULTIPLICATION_FACTOR >= 1.1,
                "Growth factor should be >= 1.1.");
 
  std::size_t m_mod;
};
 
namespace detail {
 
#if SIZE_MAX >= ULLONG_MAX
#define TSL_RH_NB_PRIMES 51
#elif SIZE_MAX >= ULONG_MAX
#define TSL_RH_NB_PRIMES 40
#else
#define TSL_RH_NB_PRIMES 23
#endif
 
static constexpr const std::array<std::size_t, TSL_RH_NB_PRIMES> PRIMES = {{
    1u,
    5u,
    17u,
    29u,
    37u,
    53u,
    67u,
    79u,
    97u,
    131u,
    193u,
    257u,
    389u,
    521u,
    769u,
    1031u,
    1543u,
    2053u,
    3079u,
    6151u,
    12289u,
    24593u,
    49157u,
#if SIZE_MAX >= ULONG_MAX
    98317ul,
    196613ul,
    393241ul,
    786433ul,
    1572869ul,
    3145739ul,
    6291469ul,
    12582917ul,
    25165843ul,
    50331653ul,
    100663319ul,
    201326611ul,
    402653189ul,
    805306457ul,
    1610612741ul,
    3221225473ul,
    4294967291ul,
#endif
#if SIZE_MAX >= ULLONG_MAX
    6442450939ull,
    12884901893ull,
    25769803751ull,
    51539607551ull,
    103079215111ull,
    206158430209ull,
    412316860441ull,
    824633720831ull,
    1649267441651ull,
    3298534883309ull,
    6597069766657ull,
#endif
}};
 
template <unsigned int IPrime>
static constexpr std::size_t mod(std::size_t hash) {
  return hash % PRIMES[IPrime];
}
 
// MOD_PRIME[iprime](hash) returns hash % PRIMES[iprime]. This table allows for
// faster modulo as the compiler can optimize the modulo code better with a
// constant known at the compilation.
static constexpr const std::array<std::size_t (*)(std::size_t),
                                  TSL_RH_NB_PRIMES>
    MOD_PRIME = {{
        &mod<0>,  &mod<1>,  &mod<2>,  &mod<3>,  &mod<4>,  &mod<5>,
        &mod<6>,  &mod<7>,  &mod<8>,  &mod<9>,  &mod<10>, &mod<11>,
        &mod<12>, &mod<13>, &mod<14>, &mod<15>, &mod<16>, &mod<17>,
        &mod<18>, &mod<19>, &mod<20>, &mod<21>, &mod<22>,
#if SIZE_MAX >= ULONG_MAX
        &mod<23>, &mod<24>, &mod<25>, &mod<26>, &mod<27>, &mod<28>,
        &mod<29>, &mod<30>, &mod<31>, &mod<32>, &mod<33>, &mod<34>,
        &mod<35>, &mod<36>, &mod<37>, &mod<38>, &mod<39>,
#endif
#if SIZE_MAX >= ULLONG_MAX
        &mod<40>, &mod<41>, &mod<42>, &mod<43>, &mod<44>, &mod<45>,
        &mod<46>, &mod<47>, &mod<48>, &mod<49>, &mod<50>,
#endif
    }};
 
}  // namespace detail
 
class prime_growth_policy {
 public:
  explicit prime_growth_policy(std::size_t& min_bucket_count_in_out) {
    auto it_prime = std::lower_bound(
        detail::PRIMES.begin(), detail::PRIMES.end(), min_bucket_count_in_out);
    if (it_prime == detail::PRIMES.end()) {
      TSL_RH_THROW_OR_TERMINATE(std::length_error,
                                "The hash table exceeds its maximum size.");
    }
 
    m_iprime = static_cast<unsigned int>(
        std::distance(detail::PRIMES.begin(), it_prime));
    if (min_bucket_count_in_out > 0) {
      min_bucket_count_in_out = *it_prime;
    } else {
      min_bucket_count_in_out = 0;
    }
  }
 
  std::size_t bucket_for_hash(std::size_t hash) const noexcept {
    return detail::MOD_PRIME[m_iprime](hash);
  }
 
  std::size_t next_bucket_count() const {
    if (m_iprime + 1 >= detail::PRIMES.size()) {
      TSL_RH_THROW_OR_TERMINATE(std::length_error,
                                "The hash table exceeds its maximum size.");
    }
 
    return detail::PRIMES[m_iprime + 1];
  }
 
  std::size_t max_bucket_count() const { return detail::PRIMES.back(); }
 
  void clear() noexcept { m_iprime = 0; }
 
 private:
  unsigned int m_iprime;
 
  static_assert(std::numeric_limits<decltype(m_iprime)>::max() >=
                    detail::PRIMES.size(),
                "The type of m_iprime is not big enough.");
};
 
}  // namespace rh
}  // namespace tsl
 
#endif