348 lines
12 KiB
C++
348 lines
12 KiB
C++
/**
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* MIT License
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*
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* Copyright (c) 2017 Thibaut Goetghebuer-Planchon <tessil@gmx.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#ifndef TSL_ROBIN_GROWTH_POLICY_H
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#define TSL_ROBIN_GROWTH_POLICY_H
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#include <algorithm>
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#include <array>
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#include <climits>
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#include <cmath>
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#include <cstddef>
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#include <cstdint>
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#include <iterator>
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#include <limits>
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#include <ratio>
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#include <stdexcept>
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#ifdef TSL_DEBUG
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# define tsl_rh_assert(expr) assert(expr)
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#else
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# define tsl_rh_assert(expr) (static_cast<void>(0))
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#endif
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/**
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* If exceptions are enabled, throw the exception passed in parameter, otherwise call std::terminate.
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*/
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#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || (defined (_MSC_VER) && defined (_CPPUNWIND))) && !defined(TSL_NO_EXCEPTIONS)
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# define TSL_RH_THROW_OR_TERMINATE(ex, msg) throw ex(msg)
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#else
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# define TSL_RH_NO_EXCEPTIONS
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# ifdef NDEBUG
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# define TSL_RH_THROW_OR_TERMINATE(ex, msg) std::terminate()
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# else
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# include <iostream>
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# define TSL_RH_THROW_OR_TERMINATE(ex, msg) do { std::cerr << msg << std::endl; std::terminate(); } while(0)
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# endif
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#endif
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#if defined(__GNUC__) || defined(__clang__)
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# define TSL_RH_LIKELY(exp) (__builtin_expect(!!(exp), true))
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#else
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# define TSL_RH_LIKELY(exp) (exp)
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#endif
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namespace tsl {
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namespace rh {
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/**
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* Grow the hash table by a factor of GrowthFactor keeping the bucket count to a power of two. It allows
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* the table to use a mask operation instead of a modulo operation to map a hash to a bucket.
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*
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* GrowthFactor must be a power of two >= 2.
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*/
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template<std::size_t GrowthFactor>
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class power_of_two_growth_policy {
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public:
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/**
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* Called on the hash table creation and on rehash. The number of buckets for the table is passed in parameter.
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* This number is a minimum, the policy may update this value with a higher value if needed (but not lower).
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*
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* If 0 is given, min_bucket_count_in_out must still be 0 after the policy creation and
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* bucket_for_hash must always return 0 in this case.
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*/
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explicit power_of_two_growth_policy(std::size_t& min_bucket_count_in_out) {
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if(min_bucket_count_in_out > max_bucket_count()) {
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TSL_RH_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maximum size.");
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}
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if(min_bucket_count_in_out > 0) {
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min_bucket_count_in_out = round_up_to_power_of_two(min_bucket_count_in_out);
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m_mask = min_bucket_count_in_out - 1;
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}
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else {
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m_mask = 0;
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}
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}
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/**
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* Return the bucket [0, bucket_count()) to which the hash belongs.
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* If bucket_count() is 0, it must always return 0.
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*/
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std::size_t bucket_for_hash(std::size_t hash) const noexcept {
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return hash & m_mask;
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}
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/**
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* Return the number of buckets that should be used on next growth.
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*/
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std::size_t next_bucket_count() const {
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if((m_mask + 1) > max_bucket_count() / GrowthFactor) {
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TSL_RH_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maximum size.");
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}
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return (m_mask + 1) * GrowthFactor;
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}
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/**
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* Return the maximum number of buckets supported by the policy.
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*/
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std::size_t max_bucket_count() const {
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// Largest power of two.
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return (std::numeric_limits<std::size_t>::max() / 2) + 1;
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}
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/**
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* Reset the growth policy as if it was created with a bucket count of 0.
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* After a clear, the policy must always return 0 when bucket_for_hash is called.
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*/
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void clear() noexcept {
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m_mask = 0;
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}
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private:
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static std::size_t round_up_to_power_of_two(std::size_t value) {
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if(is_power_of_two(value)) {
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return value;
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}
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if(value == 0) {
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return 1;
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}
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--value;
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for(std::size_t i = 1; i < sizeof(std::size_t) * CHAR_BIT; i *= 2) {
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value |= value >> i;
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}
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return value + 1;
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}
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static constexpr bool is_power_of_two(std::size_t value) {
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return value != 0 && (value & (value - 1)) == 0;
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}
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protected:
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static_assert(is_power_of_two(GrowthFactor) && GrowthFactor >= 2, "GrowthFactor must be a power of two >= 2.");
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std::size_t m_mask;
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};
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/**
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* Grow the hash table by GrowthFactor::num / GrowthFactor::den and use a modulo to map a hash
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* to a bucket. Slower but it can be useful if you want a slower growth.
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*/
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template<class GrowthFactor = std::ratio<3, 2>>
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class mod_growth_policy {
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public:
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explicit mod_growth_policy(std::size_t& min_bucket_count_in_out) {
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if(min_bucket_count_in_out > max_bucket_count()) {
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TSL_RH_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maximum size.");
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}
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if(min_bucket_count_in_out > 0) {
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m_mod = min_bucket_count_in_out;
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}
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else {
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m_mod = 1;
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}
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}
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std::size_t bucket_for_hash(std::size_t hash) const noexcept {
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return hash % m_mod;
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}
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std::size_t next_bucket_count() const {
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if(m_mod == max_bucket_count()) {
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TSL_RH_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maximum size.");
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}
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const double next_bucket_count = std::ceil(double(m_mod) * REHASH_SIZE_MULTIPLICATION_FACTOR);
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if(!std::isnormal(next_bucket_count)) {
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TSL_RH_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maximum size.");
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}
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if(next_bucket_count > double(max_bucket_count())) {
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return max_bucket_count();
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}
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else {
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return std::size_t(next_bucket_count);
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}
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}
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std::size_t max_bucket_count() const {
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return MAX_BUCKET_COUNT;
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}
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void clear() noexcept {
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m_mod = 1;
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}
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private:
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static constexpr double REHASH_SIZE_MULTIPLICATION_FACTOR = 1.0 * GrowthFactor::num / GrowthFactor::den;
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static const std::size_t MAX_BUCKET_COUNT =
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std::size_t(double(
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std::numeric_limits<std::size_t>::max() / REHASH_SIZE_MULTIPLICATION_FACTOR
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));
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static_assert(REHASH_SIZE_MULTIPLICATION_FACTOR >= 1.1, "Growth factor should be >= 1.1.");
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std::size_t m_mod;
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};
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namespace detail {
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#if SIZE_MAX >= ULLONG_MAX
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#define TSL_RH_NB_PRIMES 51
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#elif SIZE_MAX >= ULONG_MAX
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#define TSL_RH_NB_PRIMES 40
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#else
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#define TSL_RH_NB_PRIMES 23
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#endif
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static constexpr const std::array<std::size_t, TSL_RH_NB_PRIMES> PRIMES = {{
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1u, 5u, 17u, 29u, 37u, 53u, 67u, 79u, 97u, 131u, 193u, 257u, 389u, 521u, 769u, 1031u,
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1543u, 2053u, 3079u, 6151u, 12289u, 24593u, 49157u,
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#if SIZE_MAX >= ULONG_MAX
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98317ul, 196613ul, 393241ul, 786433ul, 1572869ul, 3145739ul, 6291469ul, 12582917ul,
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25165843ul, 50331653ul, 100663319ul, 201326611ul, 402653189ul, 805306457ul, 1610612741ul,
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3221225473ul, 4294967291ul,
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#endif
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#if SIZE_MAX >= ULLONG_MAX
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6442450939ull, 12884901893ull, 25769803751ull, 51539607551ull, 103079215111ull, 206158430209ull,
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412316860441ull, 824633720831ull, 1649267441651ull, 3298534883309ull, 6597069766657ull,
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#endif
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}};
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template<unsigned int IPrime>
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static constexpr std::size_t mod(std::size_t hash) { return hash % PRIMES[IPrime]; }
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// MOD_PRIME[iprime](hash) returns hash % PRIMES[iprime]. This table allows for faster modulo as the
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// compiler can optimize the modulo code better with a constant known at the compilation.
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static constexpr const std::array<std::size_t(*)(std::size_t), TSL_RH_NB_PRIMES> MOD_PRIME = {{
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&mod<0>, &mod<1>, &mod<2>, &mod<3>, &mod<4>, &mod<5>, &mod<6>, &mod<7>, &mod<8>, &mod<9>, &mod<10>,
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&mod<11>, &mod<12>, &mod<13>, &mod<14>, &mod<15>, &mod<16>, &mod<17>, &mod<18>, &mod<19>, &mod<20>,
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&mod<21>, &mod<22>,
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#if SIZE_MAX >= ULONG_MAX
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&mod<23>, &mod<24>, &mod<25>, &mod<26>, &mod<27>, &mod<28>, &mod<29>, &mod<30>, &mod<31>, &mod<32>,
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&mod<33>, &mod<34>, &mod<35>, &mod<36>, &mod<37> , &mod<38>, &mod<39>,
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#endif
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#if SIZE_MAX >= ULLONG_MAX
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&mod<40>, &mod<41>, &mod<42>, &mod<43>, &mod<44>, &mod<45>, &mod<46>, &mod<47>, &mod<48>, &mod<49>,
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&mod<50>,
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#endif
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}};
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}
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/**
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* Grow the hash table by using prime numbers as bucket count. Slower than tsl::rh::power_of_two_growth_policy in
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* general but will probably distribute the values around better in the buckets with a poor hash function.
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*
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* To allow the compiler to optimize the modulo operation, a lookup table is used with constant primes numbers.
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*
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* With a switch the code would look like:
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* \code
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* switch(iprime) { // iprime is the current prime of the hash table
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* case 0: hash % 5ul;
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* break;
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* case 1: hash % 17ul;
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* break;
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* case 2: hash % 29ul;
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* break;
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* ...
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* }
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* \endcode
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*
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* Due to the constant variable in the modulo the compiler is able to optimize the operation
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* by a series of multiplications, substractions and shifts.
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*
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* The 'hash % 5' could become something like 'hash - (hash * 0xCCCCCCCD) >> 34) * 5' in a 64 bits environment.
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*/
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class prime_growth_policy {
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public:
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explicit prime_growth_policy(std::size_t& min_bucket_count_in_out) {
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auto it_prime = std::lower_bound(detail::PRIMES.begin(),
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detail::PRIMES.end(), min_bucket_count_in_out);
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if(it_prime == detail::PRIMES.end()) {
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TSL_RH_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maximum size.");
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}
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m_iprime = static_cast<unsigned int>(std::distance(detail::PRIMES.begin(), it_prime));
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if(min_bucket_count_in_out > 0) {
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min_bucket_count_in_out = *it_prime;
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}
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else {
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min_bucket_count_in_out = 0;
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}
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}
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std::size_t bucket_for_hash(std::size_t hash) const noexcept {
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return detail::MOD_PRIME[m_iprime](hash);
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}
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std::size_t next_bucket_count() const {
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if(m_iprime + 1 >= detail::PRIMES.size()) {
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TSL_RH_THROW_OR_TERMINATE(std::length_error, "The hash table exceeds its maximum size.");
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}
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return detail::PRIMES[m_iprime + 1];
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}
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std::size_t max_bucket_count() const {
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return detail::PRIMES.back();
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}
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void clear() noexcept {
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m_iprime = 0;
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}
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private:
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unsigned int m_iprime;
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static_assert(std::numeric_limits<decltype(m_iprime)>::max() >= detail::PRIMES.size(),
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"The type of m_iprime is not big enough.");
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};
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}
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}
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#endif
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