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memory: turn the power-of-two/fast_mod toolset into a non-constexpr one

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This commit is contained in:
Michele Caini
2022-10-21 11:01:18 +02:00
parent 7c58c83ee0
commit 57ad7696be
2 changed files with 39 additions and 48 deletions
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72
src/entt/core/memory.hpp
View File

@@ -11,6 +11,42 @@
namespace entt {
/**
* @brief Checks whether a value is a power of two or not.
* @param value A value that may or may not be a power of two.
* @return True if the value is a power of two, false otherwise.
*/
[[nodiscard]] inline bool is_power_of_two(const std::size_t value) noexcept {
return value && ((value & (value - 1)) == 0);
}
/**
* @brief Computes the smallest power of two greater than or equal to a value.
* @param value The value to use.
* @return The smallest power of two greater than or equal to the given value.
*/
[[nodiscard]] inline std::size_t next_power_of_two(const std::size_t value) noexcept {
ENTT_ASSERT(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
std::size_t curr = value - (value != 0u);
for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
curr |= curr >> next;
}
return ++curr;
}
/**
* @brief Fast module utility function (powers of two only).
* @param value A value for which to calculate the modulus.
* @param mod _Modulus_, it must be a power of two.
* @return The common remainder.
*/
[[nodiscard]] inline std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
ENTT_ASSERT(is_power_of_two(mod), "Value must be a power of two");
return value & (mod - 1u);
}
/**
* @brief Unwraps fancy pointers, does nothing otherwise (waiting for C++20).
* @tparam Type Pointer type.
@@ -68,42 +104,6 @@ constexpr void propagate_on_container_swap([[maybe_unused]] Allocator &lhs, [[ma
}
}
/**
* @brief Checks whether a value is a power of two or not.
* @param value A value that may or may not be a power of two.
* @return True if the value is a power of two, false otherwise.
*/
[[nodiscard]] inline constexpr bool is_power_of_two(const std::size_t value) noexcept {
return value && ((value & (value - 1)) == 0);
}
/**
* @brief Computes the smallest power of two greater than or equal to a value.
* @param value The value to use.
* @return The smallest power of two greater than or equal to the given value.
*/
[[nodiscard]] inline constexpr std::size_t next_power_of_two(const std::size_t value) noexcept {
ENTT_ASSERT(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
std::size_t curr = value - (value != 0u);
for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
curr |= curr >> next;
}
return ++curr;
}
/**
* @brief Fast module utility function (powers of two only).
* @param value A value for which to calculate the modulus.
* @param mod _Modulus_, it must be a power of two.
* @return The common remainder.
*/
[[nodiscard]] inline constexpr std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
ENTT_ASSERT(is_power_of_two(mod), "Value must be a power of two");
return value & (mod - 1u);
}
/**
* @brief Deleter for allocator-aware unique pointers (waiting for C++20).
* @tparam Args Types of arguments to use to construct the object.

15
test/entt/core/memory.cpp
View File

@@ -37,10 +37,7 @@ ENTT_DEBUG_TEST(PoccaPocmaAndPocsDeathTest, Functionalities) {
}
TEST(IsPowerOfTwo, Functionalities) {
// constexpr-ness guaranteed
constexpr auto zero_is_power_of_two = entt::is_power_of_two(0u);
ASSERT_FALSE(zero_is_power_of_two);
ASSERT_FALSE(entt::is_power_of_two(0u));
ASSERT_TRUE(entt::is_power_of_two(1u));
ASSERT_TRUE(entt::is_power_of_two(2u));
ASSERT_TRUE(entt::is_power_of_two(4u));
@@ -50,10 +47,7 @@ TEST(IsPowerOfTwo, Functionalities) {
}
TEST(NextPowerOfTwo, Functionalities) {
// constexpr-ness guaranteed
constexpr auto next_power_of_two_of_zero = entt::next_power_of_two(0u);
ASSERT_EQ(next_power_of_two_of_zero, 1u);
ASSERT_EQ(entt::next_power_of_two(0u), 1u);
ASSERT_EQ(entt::next_power_of_two(1u), 1u);
ASSERT_EQ(entt::next_power_of_two(2u), 2u);
ASSERT_EQ(entt::next_power_of_two(3u), 4u);
@@ -69,10 +63,7 @@ ENTT_DEBUG_TEST(NextPowerOfTwoDeathTest, Functionalities) {
}
TEST(FastMod, Functionalities) {
// constexpr-ness guaranteed
constexpr auto fast_mod_of_zero = entt::fast_mod(0u, 8u);
ASSERT_EQ(fast_mod_of_zero, 0u);
ASSERT_EQ(entt::fast_mod(0u, 8u), 0u);
ASSERT_EQ(entt::fast_mod(7u, 8u), 7u);
ASSERT_EQ(entt::fast_mod(8u, 8u), 0u);
}