From c8df88d8c61197d8f019efa0ba373ed14a28d914 Mon Sep 17 00:00:00 2001
From: Bardur Arantsson <bardur@scientician.net>
Date: Tue, 29 Mar 2016 20:32:55 +0200
Subject: Introduce new way of handling flags

---
 src/CMakeLists.txt                       |   1 +
 src/flag_set.hpp                         | 144 +++++++++++++++++++++++++++++++
 src/include/tome/pp/global_constexpr.hpp |  21 +++++
 3 files changed, 166 insertions(+)
 create mode 100644 src/flag_set.hpp
 create mode 100644 src/include/tome/pp/global_constexpr.hpp

(limited to 'src')

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 6d942dfe..a68e056b 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -118,6 +118,7 @@ SET(SRCS_TESTS
   ../tests/get_level_device.cc
   ../tests/harness.cc
   ../tests/lua_get_level.cc
+  ../tests/flag_set.cc
 )
 
 ADD_LIBRARY(game
diff --git a/src/flag_set.hpp b/src/flag_set.hpp
new file mode 100644
index 00000000..cbc4e7aa
--- /dev/null
+++ b/src/flag_set.hpp
@@ -0,0 +1,144 @@
+#pragma once
+
+#include <array>
+#include <cassert>
+#include <cstdint>
+
+#include "tome/pp/global_constexpr.hpp"
+
+/**
+ * Set of binary flags.
+ */
+template<std::size_t Tiers> struct flag_set
+{
+private:
+	static constexpr std::size_t tiers = Tiers;
+	std::uint32_t m_data[tiers];
+
+public:
+
+	constexpr flag_set()
+		: m_data { 0 }
+	{
+		// It is *extremely* important that there are absolutely
+		// NO dependencies on any global objects in here; lest we
+		// fall into SIOF territory; see DECLARE_FLAG_ZERO_IMPL
+	}
+
+	// This method is a workaround for a a segmentation fault
+	// when compiling with GCC 5.3.0 (Arch Linux). We should be
+	// able to use make() directly in DECLARE_FLAG_MAKE_INIT,
+	// but GCC segfaults.
+	template<std::uint32_t tier, std::size_t index> static constexpr flag_set make_static()
+	{
+		static_assert(tier < tiers, "tier >= tiers");
+		static_assert(index < 32, "index >= 32");
+		flag_set f;
+		f.m_data[tier] = (1UL << index);
+		return f;
+	}
+
+	static constexpr flag_set make(std::uint32_t tier, std::size_t index)
+	{
+		assert(tier < tiers);
+		assert(index < 32);
+		flag_set f;
+		f.m_data[tier] = (1UL << index);
+		return f;
+	}
+
+	constexpr std::size_t size() const
+	{
+		return tiers;
+	}
+
+	constexpr bool empty() const
+	{
+		for (std::size_t i = 0; i < tiers; i++)
+		{
+			if (m_data[i])
+			{
+				return false;
+			}
+		}
+		return true;
+	}
+
+	uint32_t &operator[](std::size_t i)
+	{
+		assert(i < tiers);
+		return m_data[i];
+	}
+
+	constexpr uint32_t const &operator [](std::size_t i) const
+	{
+		assert(i < tiers);
+		return m_data[i];
+	}
+
+	constexpr operator bool() const
+	{
+		return !empty();
+	}
+
+	flag_set &operator |= (flag_set const &other)
+	{
+		for (std::size_t i = 0; i < tiers; i++)
+		{
+			m_data[i] |= other.m_data[i];
+		}
+		return *this;
+	}
+
+	constexpr flag_set operator | (flag_set const &other) const
+	{
+		flag_set f;
+		for (std::size_t i = 0; i < tiers; i++)
+		{
+			f.m_data[i] = m_data[i] | other.m_data[i];
+		}
+		return f;
+	}
+
+	flag_set &operator &= (flag_set const &other)
+	{
+		for (std::size_t i = 0; i < tiers; i++)
+		{
+			m_data[i] &= other.m_data[i];
+		}
+		return *this;
+	}
+
+	constexpr flag_set operator & (flag_set const &other) const
+	{
+		flag_set f;
+		for (std::size_t i = 0; i < tiers; i++)
+		{
+			f.m_data[i] = m_data[i] & other.m_data[i];
+		}
+		return f;
+	}
+
+};
+
+// Implementation details, because preprocessor.
+#define DECLARE_FLAG_MAKE_INIT(type, tier, index) \
+   type::make_static<tier-1,index>()
+
+/**
+ * Macro for declaring a "flag" constant.
+ */
+#define DECLARE_FLAG(type, name, tier, index) \
+  PP_GLOBAL_CONSTEXPR_CONST(type, name, DECLARE_FLAG_MAKE_INIT(type, tier, index))
+
+/**
+ * Macro for declaring a zero'ed "flag" variable.
+ */
+#define DECLARE_FLAG_ZERO_INTF(type, name) \
+  extern type name
+
+/**
+ * Macro for declaring the implementation of a zero'ed "flag" variable.
+ */
+#define DECLARE_FLAG_ZERO_IMPL(type, name) \
+  type name { };
diff --git a/src/include/tome/pp/global_constexpr.hpp b/src/include/tome/pp/global_constexpr.hpp
new file mode 100644
index 00000000..83168c59
--- /dev/null
+++ b/src/include/tome/pp/global_constexpr.hpp
@@ -0,0 +1,21 @@
+#pragma once
+
+/**
+ * Macro for declaring a global constexpr variable without
+ * violating the ODR and without running into the SIOF.
+ *
+ * Shamelessly cribbed from http://stackoverflow.com/a/20374473
+ */
+#define PP_GLOBAL_CONSTEXPR_CONST(type, var, value)                      \
+namespace global_constexpr { namespace var {                             \
+template<class = void>                                                   \
+struct wrapper                                                           \
+{                                                                        \
+     static constexpr type var = value;                                  \
+};                                                                       \
+template<class T>                                                        \
+constexpr type wrapper<T>::var;                                          \
+} }                                                                      \
+namespace {                                                              \
+auto const& var = global_constexpr::var::wrapper<>::var;                 \
+}
-- 
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