From 20f3bef6bdbf1b2463f9b8560cfce8e7e5f02eb7 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Sun, 12 Jan 2025 20:05:35 +0300
Subject: [PATCH] Add random::poisson distribution

---
 libs/random/include/psemek/random/poisson.hpp | 39 +++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 libs/random/include/psemek/random/poisson.hpp

diff --git a/libs/random/include/psemek/random/poisson.hpp b/libs/random/include/psemek/random/poisson.hpp
new file mode 100644
index 00000000..d86dfc20
--- /dev/null
+++ b/libs/random/include/psemek/random/poisson.hpp
@@ -0,0 +1,39 @@
+#pragma once
+
+#include <psemek/random/uniform.hpp>
+
+#include <cmath>
+
+namespace psemek::random
+{
+
+	template <typename T>
+	struct poisson_distribution
+	{
+		poisson_distribution(T lambda)
+			: exp_mlambda_(std::exp(-lambda))
+		{}
+
+		template <typename RNG>
+		std::size_t operator()(RNG & rng)
+		{
+			// Knuth's method
+
+			std::size_t result = 0;
+			T product = T{1};
+
+			do
+			{
+				++result;
+				product *= uniform<T>(rng);
+			}
+			while (product > exp_mlambda_);
+
+			return result - 1;
+		}
+
+	private:
+		T exp_mlambda_;
+	};
+
+}