From ea6af75e8e1f6d4efe4bd18813fd6cf0d45c5a2d Mon Sep 17 00:00:00 2001
From: Michele Caini <michele.caini@gmail.com>
Date: Sun, 29 Aug 2021 22:45:16 +0200
Subject: [PATCH] memory: added utility function fast_mod

---
 src/entt/core/memory.hpp  | 13 +++++++++++++
 test/entt/core/memory.cpp |  6 ++++++
 2 files changed, 19 insertions(+)

diff --git a/src/entt/core/memory.hpp b/src/entt/core/memory.hpp
index 116ec5866..220483c25 100644
--- a/src/entt/core/memory.hpp
+++ b/src/entt/core/memory.hpp
@@ -89,6 +89,19 @@ template<std::size_t Value>
 inline constexpr bool is_power_of_two_v = is_power_of_two<Value>::value;
 
 
+/**
+ * @brief Fast module utility function (powers of two only).
+ * @tparam Value Compile-time page size, it must be a power of two.
+ * @param value A value for which to calculate the modulus.
+ * @return Remainder of division.
+ */
+template<std::size_t Value>
+[[nodiscard]] constexpr std::size_t fast_mod(const std::size_t value) ENTT_NOEXCEPT {
+    static_assert(is_power_of_two_v<Value>, "Value must be a power of two");
+    return value & (Value - 1u);
+}
+
+
 }
 
 
diff --git a/test/entt/core/memory.cpp b/test/entt/core/memory.cpp
index 0e5888712..14fe58877 100644
--- a/test/entt/core/memory.cpp
+++ b/test/entt/core/memory.cpp
@@ -41,3 +41,9 @@ TEST(Memory, IsPowerOfTwo) {
     ASSERT_TRUE(entt::is_power_of_two_v<128u>);
     ASSERT_FALSE(entt::is_power_of_two_v<200u>);
 }
+
+TEST(Memory, FastMod) {
+    ASSERT_EQ(entt::fast_mod<8u>(0u), 0u);
+    ASSERT_EQ(entt::fast_mod<8u>(7u), 7u);
+    ASSERT_EQ(entt::fast_mod<8u>(8u), 0u);
+}