/** * MIT License * * Copyright (c) 2017 Tessil * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in all * copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE * SOFTWARE. */ #ifndef TSL_ROBIN_GROWTH_POLICY_H #define TSL_ROBIN_GROWTH_POLICY_H #include #include #include #include #include #include #include #include #include #ifndef tsl_assert # ifdef TSL_DEBUG # define tsl_assert(expr) assert(expr) # else # define tsl_assert(expr) (static_cast(0)) # endif #endif /** * If exceptions are enabled, throw the exception passed in parameter, otherwise call std::terminate. */ #ifndef TSL_THROW_OR_TERMINATE # if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || (defined (_MSC_VER) && defined (_CPPUNWIND))) && !defined(TSL_NO_EXCEPTIONS) # define TSL_THROW_OR_TERMINATE(ex, msg) throw ex(msg) # else # ifdef NDEBUG # define TSL_THROW_OR_TERMINATE(ex, msg) std::terminate() # else # include # define TSL_THROW_OR_TERMINATE(ex, msg) do { std::fprintf(stderr, msg); std::terminate(); } while(0) # endif # endif #endif #ifndef TSL_LIKELY # if defined(__GNUC__) || defined(__clang__) # define TSL_LIKELY(exp) (__builtin_expect(!!(exp), true)) # else # define TSL_LIKELY(exp) (exp) # endif #endif namespace tsl { namespace rh { /** * Grow the hash table by a factor of GrowthFactor keeping the bucket count to a power of two. It allows * the table to use a mask operation instead of a modulo operation to map a hash to a bucket. * * GrowthFactor must be a power of two >= 2. */ template class power_of_two_growth_policy { public: /** * Called on the hash table creation and on rehash. The number of buckets for the table is passed in parameter. * This number is a minimum, the policy may update this value with a higher value if needed (but not lower). * * If 0 is given, min_bucket_count_in_out must still be 0 after the policy creation and * bucket_for_hash must always return 0 in this case. */ explicit power_of_two_growth_policy(std::size_t& min_bucket_count_in_out) { if(min_bucket_count_in_out > max_bucket_count()) { TSL_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maxmimum 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; } } /** * Return the bucket [0, bucket_count()) to which the hash belongs. * If bucket_count() is 0, it must always return 0. */ std::size_t bucket_for_hash(std::size_t hash) const noexcept { return hash & m_mask; } /** * Return the number of buckets that should be used on next growth. */ std::size_t next_bucket_count() const { if((m_mask + 1) > max_bucket_count() / GrowthFactor) { TSL_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maxmimum size."); } return (m_mask + 1) * GrowthFactor; } /** * Return the maximum number of buckets supported by the policy. */ std::size_t max_bucket_count() const { // Largest power of two. return ((std::numeric_limits::max)() / 2) + 1; } /** * Reset the growth policy as if it was created with a bucket count of 0. * After a clear, the policy must always return 0 when bucket_for_hash is called. */ 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; }; /** * Grow the hash table by GrowthFactor::num / GrowthFactor::den and use a modulo to map a hash * to a bucket. Slower but it can be useful if you want a slower growth. */ template> 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_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maxmimum 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_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maxmimum size."); } const double next_bucket_count = std::ceil(double(m_mod) * REHASH_SIZE_MULTIPLICATION_FACTOR); if(!std::isnormal(next_bucket_count)) { TSL_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maxmimum 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::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 { static constexpr const std::array PRIMES = {{ 1ul, 5ul, 17ul, 29ul, 37ul, 53ul, 67ul, 79ul, 97ul, 131ul, 193ul, 257ul, 389ul, 521ul, 769ul, 1031ul, 1543ul, 2053ul, 3079ul, 6151ul, 12289ul, 24593ul, 49157ul, 98317ul, 196613ul, 393241ul, 786433ul, 1572869ul, 3145739ul, 6291469ul, 12582917ul, 25165843ul, 50331653ul, 100663319ul, 201326611ul, 402653189ul, 805306457ul, 1610612741ul, 3221225473ul, 4294967291ul }}; template 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 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>, &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> }}; } /** * Grow the hash table by using prime numbers as bucket count. Slower than tsl::rh::power_of_two_growth_policy in * general but will probably distribute the values around better in the buckets with a poor hash function. * * To allow the compiler to optimize the modulo operation, a lookup table is used with constant primes numbers. * * With a switch the code would look like: * \code * switch(iprime) { // iprime is the current prime of the hash table * case 0: hash % 5ul; * break; * case 1: hash % 17ul; * break; * case 2: hash % 29ul; * break; * ... * } * \endcode * * Due to the constant variable in the modulo the compiler is able to optimize the operation * by a series of multiplications, substractions and shifts. * * The 'hash % 5' could become something like 'hash - (hash * 0xCCCCCCCD) >> 34) * 5' in a 64 bits environement. */ 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_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maxmimum size."); } m_iprime = static_cast(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_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maxmimum 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::max)() >= detail::PRIMES.size(), "The type of m_iprime is not big enough."); }; } } #endif