+ xoshiro256ss (copied from kalman project)

include/randomgen/engine_concept.hpp

@@ -0,0 +1,36 @@
+/* @file engine_concept.hpp */
+
+#pragma once
+
+#include <concepts>
+#include <random>
+
+namespace xo {
+    namespace rng {
+        /* an engine generates psuedo-random bits.
+         * given
+         *   RngEngine eng = ...;
+         *
+         *   RngEngine::result_type x = eng();
+         *
+         * puts random bits into x.
+         */
+        template <class RngEngine>
+        concept engine_concept = requires(RngEngine engine, typename RngEngine::result_type r) {
+            /* note: the first 4 requirements characterize UniformRandomBitGenerator */
+            typename RngEngine::result_type;
+            { RngEngine(r) };
+            { engine.min() } -> std::same_as<typename RngEngine::result_type>;
+            { engine.max() } -> std::same_as<typename RngEngine::result_type>;
+            /* must return value in closed interval [.min(), .max()] */
+            { engine() } -> std::same_as<typename RngEngine::result_type>;
+
+            { engine.seed() };
+            { engine.seed(r) };
+            { engine == engine };
+            { engine != engine };
+        } && std::copyable<RngEngine> && std::uniform_random_bit_generator<RngEngine>;
+    } /*namespace rng*/
+} /*namespace xo*/
+
+/* end engine_concept.hpp */