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axmol/external/tsl/robin_growth_policy.h

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/**
* MIT License
*
* Copyright (c) 2017 Thibaut Goetghebuer-Planchon <tessil@gmx.com>
*
* 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 NDEBUG
#define TSL_RH_THROW_OR_TERMINATE(ex, msg) std::terminate()
#else
#include <iostream>
#define TSL_RH_THROW_OR_TERMINATE(ex, msg) \
do { \
std::cerr << msg << std::endl; \
std::terminate(); \
} while (0)
#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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