From 8d1be9aebca1a9b2e0709d9115e9891b64182aa3 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Sun, 7 Mar 2021 21:18:27 +0300
Subject: [PATCH] Add pcg::chunked_map

---
 libs/pcg/include/psemek/pcg/chunked_map.hpp | 55 +++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 libs/pcg/include/psemek/pcg/chunked_map.hpp

diff --git a/libs/pcg/include/psemek/pcg/chunked_map.hpp b/libs/pcg/include/psemek/pcg/chunked_map.hpp
new file mode 100644
index 00000000..d5312c8f
--- /dev/null
+++ b/libs/pcg/include/psemek/pcg/chunked_map.hpp
@@ -0,0 +1,55 @@
+#pragma once
+
+#include <psemek/util/function.hpp>
+#include <psemek/util/array.hpp>
+#include <psemek/geom/box.hpp>
+
+#include <unordered_map>
+
+namespace psemek::pcg
+{
+
+	template <typename T, std::size_t N>
+	struct chunked_map
+	{
+		using generator_func = util::function<util::array<T, N>(geom::box<int, N> const &)>;
+
+		chunked_map(std::size_t chunk_size, generator_func generator)
+			: chunk_size_(chunk_size)
+			, generator_(std::move(generator))
+		{}
+
+		T const & operator()(geom::vector<int, N> p)
+		{
+			geom::vector<int, N> ip;
+			for (std::size_t i = 0; i < N; ++i)
+			{
+				ip[i] = (p[i] >= 0) ? (p[i] / chunk_size_) : -((- p[i] + chunk_size_ - 1) / chunk_size_);
+			}
+
+			auto it = chunks_.find(ip);
+			if (it == chunks_.end())
+			{
+				geom::box<int, 2> box;
+				for (std::size_t i = 0; i < N; ++i)
+				{
+					box[i] = {ip[i] * chunk_size_, (ip[i] + 1) * chunk_size_};
+				}
+				it = chunks_.insert(std::pair{ip, generator_(box)}).first;
+			}
+
+			std::array<std::size_t, N> t;
+			for (std::size_t i = 0; i < N; ++i)
+				t[i] = p[i] - ip[i] * chunk_size_;
+
+			return it->second(t);
+		}
+
+	private:
+		int const chunk_size_;
+		generator_func generator_;
+		mutable std::unordered_map<geom::vector<int, N>, util::array<T, N>> chunks_;
+
+	};
+
+}