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+/**
+ * MIT License
+ *
+ * Copyright (c) 2017 Thibaut Goetghebuer-Planchon <[email protected]>
+ *
+ * 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 <algorithm>
+#include <array>
+#include <climits>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <iterator>
+#include <limits>
+#include <ratio>
+#include <stdexcept>
+
+#ifdef TSL_DEBUG
+#define tsl_rh_assert(expr) assert(expr)
+#else
+#define tsl_rh_assert(expr) (static_cast<void>(0))
+#endif
+
+/**
+ * If exceptions are enabled, throw the exception passed in parameter, otherwise
+ * call std::terminate.
+ */
+#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 {
+
+/**
+ * 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 <std::size_t GrowthFactor>
+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_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;
+ }
+ }
+
+ /**
+ * 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_RH_THROW_OR_TERMINATE(std::length_error,
+ "The hash table exceeds its maximum 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<std::size_t>::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 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
+
+/**
+ * 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 environment.
+ */
+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
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