1 files changed, 123 insertions, 0 deletions
diff --git a/src/pattern/ps.h b/src/pattern/ps.h
new file mode 100644
index 0000000..667b09f
--- /dev/null
+++ b/src/pattern/ps.h
@@ -0,0 +1,123 @@
+#pragma once
+
+#include "population.h"
+#include "propagation.h"
+
+#include <sys/mman.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+const int PROT_RW = PROT_READ | PROT_WRITE;
+
+constexpr std::uint32_t log2(std::uint32_t x) {
+	return 31 - __builtin_clz(x);
+}
+
+namespace pattern {
+
+template <concepts::Arithmetic T>
+class PS {
+private:
+	Cuboid _cuboid;
+	std::ptrdiff_t _volume;
+
+	std::string _shm_path;
+	int _shm_name;
+	int _shm_file;
+
+	std::uint8_t* _base_buffer;
+	std::uint8_t* _buffer[population::q];
+
+	T* _base[population::q];
+	T* _f[population::q];
+
+public:
+	using value_t = T;
+
+	PS(Cuboid cuboid):
+		_cuboid(cuboid)
+	{
+		const std::size_t page_size = sysconf(_SC_PAGESIZE);
+		const std::size_t line_size = sysconf(_SC_LEVEL1_DCACHE_LINESIZE);
+		const std::size_t size = ((_cuboid.volume() * sizeof(T) - 1) / page_size + 1) * page_size;
+		_volume = size / sizeof(T);
+
+		if (size % page_size != 0) {
+			throw std::invalid_argument("Array size must be multiple of PAGE_SIZE");
+		}
+
+		_shm_path = "/lbm_XXXXXX";
+		_shm_name = mkstemp(const_cast<char*>(_shm_path.data()));
+		if (_shm_name != -1) {
+			throw std::runtime_error("Could not generate unique shared memory object name");
+		}
+		// Open shared memory object as physical lattice memory
+		_shm_file = shm_open(_shm_path.c_str(), O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
+		if (_shm_file == -1) {
+			throw std::runtime_error("Failed to create shared memory object");
+		}
+		// Resize to fit lattice populations
+		if (ftruncate(_shm_file, population::q * size) == -1) {
+			throw std::runtime_error("Failed to resize shared memory object");
+		}
+
+		// Allocate virtual address space for q times two consecutive lattices
+		_base_buffer = static_cast<std::uint8_t*>(
+		  mmap(NULL, population::q * 2 * size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0));
+
+		for (unsigned iPop=0; iPop < population::q; ++iPop) {
+			_buffer[iPop] = _base_buffer + iPop * 2 * size;
+			// Map single physical lattice into virtual address space
+			mmap(_buffer[iPop]       , size, PROT_RW, MAP_SHARED | MAP_FIXED, _shm_file, iPop * size);
+			mmap(_buffer[iPop] + size, size, PROT_RW, MAP_SHARED | MAP_FIXED, _shm_file, iPop * size);
+
+			// Store base pointer for reference
+			_base[iPop] = reinterpret_cast<T*>(_buffer[iPop]);
+			// Initialize shiftable f pointer to be used for lattice access
+			_f[iPop] = _base[iPop];
+		}
+
+		// Pre-shift to reduce cache and TLB conflict misses
+		// due to alignment of start address and page-boundaries every `page_size/sizeof(T)`-steps
+		for (unsigned iPop=0; iPop < population::q; ++iPop) {
+			std::ptrdiff_t shift = iPop * (1 << log2(line_size))
+			                     + iPop * (1 << log2(page_size));
+			shift /= sizeof(T);
+			if (shift < _volume-1) {
+				_f[iPop] += shift;
+			}
+		}
+	}
+
+	~PS() {
+		munmap(_base_buffer, population::q * 2 * _volume * sizeof(T));
+		shm_unlink(_shm_path.c_str());
+		close(_shm_name);
+		unlink(_shm_path.c_str());
+	}
+
+	T* get(unsigned iPop, stage::pre_collision) {
+		return _f[iPop];
+	}
+
+	T* get(unsigned iPop, stage::post_collision) {
+		return _f[iPop];
+	}
+
+	void stream() {
+		for (unsigned iPop=0; iPop < population::q; ++iPop) {
+		  _f[iPop] -= population::offset(_cuboid, iPop);
+		}
+
+		for (unsigned iPop=0; iPop < population::q; ++iPop) {
+			if (_f[iPop] - _base[iPop] >= _volume) {
+				_f[iPop] -= _volume;
+			} else if (_f[iPop] < _base[iPop]) {
+				_f[iPop] += _volume;
+			}
+		}
+	}
+
+};
+
+}