From d80e0dbd20bb8597afe92f770e39d20440557d1f Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Sat, 25 Jun 2022 10:16:12 -0700
Subject: Demo for a coroutine-based step evaluator.

---
 aisa/aisa.cpp    |   5 ---
 aisa/aisa.h      |  73 ++++++++++++++++++++++++++++++++-
 aisa/coroutine.h | 120 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 192 insertions(+), 6 deletions(-)
 create mode 100644 aisa/coroutine.h

(limited to 'aisa')

diff --git a/aisa/aisa.cpp b/aisa/aisa.cpp
index 0c806de..97a3b17 100644
--- a/aisa/aisa.cpp
+++ b/aisa/aisa.cpp
@@ -4,9 +4,4 @@
 
 namespace aisa {
 
-    void do_something()
-    {
-        std::cout << "Hello, world!\n";
-    }
-
 }
diff --git a/aisa/aisa.h b/aisa/aisa.h
index b570d6b..8cb302e 100644
--- a/aisa/aisa.h
+++ b/aisa/aisa.h
@@ -1,7 +1,78 @@
 #pragma once
 
+#include <coroutine>
+#include <cstdint>
+#include <iostream>
+#include <optional>
+#include <utility>
+#include <vector>
+
+#include "aisa/coroutine.h"
+
 namespace aisa {
 
-    void do_something();
+    using regnum_t = std::uint_fast64_t;
+    using regval_t = std::uint64_t;
+
+    template<typename CRTP> struct EvalState {
+        CRTP & crtp() noexcept { return static_cast<CRTP &>(*this); }
+        task<regval_t> async_load_reg(regnum_t rn)
+        {
+            while (true) {
+                if (auto rv = crtp().load_reg(rn); rv.has_value())
+                    co_return *rv;
+                co_await suspend();
+            }
+        }
+    };
+
+    struct Step {
+        const std::optional<std::pair<regnum_t, regval_t>> predicate;
+        const std::vector<regnum_t> source_regs;
+        const std::vector<regnum_t> destination_regs;
+
+        std::optional<regnum_t> predicate_reg() const
+        {
+            if (predicate.has_value())
+                return predicate->first;
+            return {};
+        }
+
+        std::optional<regnum_t> expected_predicate_val() const
+        {
+            if (predicate.has_value())
+                return predicate->second;
+            return {};
+        }
+
+        template<typename State> task<void> evaluate(State &state) const
+        {
+            if (predicate.has_value()) {
+                std::cout << "checking predicate...\n";
+                std::cout << "\texpect " << predicate->second << "\n";
+                regval_t pval = co_await state.async_load_reg(predicate->first);
+                std::cout << "\tgot " << pval << "\n";
+                if (pval != predicate->second) {
+                    std::cout << "\tpredicate skipped\n";
+                    co_return;
+                } else {
+                    std::cout << "\tpredicate not skipped\n";
+                }
+            }
+            std::cout << "reading sources...\n";
+            std::vector<regval_t> source_vals;
+            source_vals.reserve(source_regs.size());
+            for (unsigned int i = 0; i < source_regs.size(); ++i) {
+                std::cout << "\tgetting source " << i << "...\n";
+                source_vals.emplace_back(co_await state.async_load_reg(source_regs[i]));
+                std::cout << "\t\tgot " << source_vals.back() << "\n";
+            }
+            std::cout << "sources:";
+            for (unsigned int i = 0; i < source_regs.size(); ++i)
+                std::cout << " " << source_regs[i] << "=" << source_vals[i];
+            std::cout << "\n";
+            std::cout << "done with evaluate\n";
+        }
+    };
 
 }
diff --git a/aisa/coroutine.h b/aisa/coroutine.h
new file mode 100644
index 0000000..40a6982
--- /dev/null
+++ b/aisa/coroutine.h
@@ -0,0 +1,120 @@
+#pragma once
+
+#include <coroutine>
+
+namespace aisa {
+
+    inline auto suspend() noexcept { return std::suspend_always{}; }
+
+    template<typename result_t> struct promise;
+
+    template<typename result_t> struct task : public std::coroutine_handle<promise<result_t>> {
+        using handle = std::coroutine_handle<struct promise<result_t>>;
+        using promise_type = struct promise<result_t>;
+        bool await_ready() const noexcept { return handle::done(); }
+        result_t await_resume() const noexcept;
+        template<typename other_t> void await_suspend(std::coroutine_handle<struct promise<other_t>> h) const noexcept;
+        std::optional<result_t> operator()() noexcept;
+    };
+
+    template<> struct task<void> : public std::coroutine_handle<promise<void>> {
+        using handle = std::coroutine_handle<struct promise<void>>;
+        using promise_type = struct promise<void>;
+        bool await_ready() const noexcept { return handle::done(); }
+        void await_resume() const noexcept;
+        template<typename other_t> void await_suspend(std::coroutine_handle<struct promise<other_t>> h) const noexcept;
+        bool operator()() noexcept;
+    };
+
+    template<typename result_t> struct promise {
+        std::coroutine_handle<> precursor;
+        std::optional<result_t> result;
+        promise() = default;
+        promise(const promise &) = delete;
+        task<result_t> get_return_object() noexcept { return task<result_t>{std::coroutine_handle<promise<result_t>>::from_promise(*this)}; }
+        std::suspend_never initial_suspend() const noexcept { return {}; }
+        std::suspend_always final_suspend() const noexcept { return {}; }
+        void unhandled_exception() { }
+        void return_value(result_t x) noexcept { result = std::move(x); }
+    };
+
+    template<> struct promise<void> {
+        std::coroutine_handle<> precursor;
+        promise() = default;
+        promise(const promise &) = delete;
+        task<void> get_return_object() noexcept { return task<void>{std::coroutine_handle<promise<void>>::from_promise(*this)}; }
+        std::suspend_never initial_suspend() const noexcept { return {}; }
+        std::suspend_always final_suspend() const noexcept { return {}; }
+        void unhandled_exception() { }
+        void return_void() noexcept { }
+    };
+
+    template<typename result_t> result_t task<result_t>::await_resume() const noexcept
+    {
+        auto x = std::move(handle::promise().result.value());
+        handle::destroy();
+        return std::move(x);
+    }
+
+    template<typename result_t> template<typename other_t> void task<result_t>::await_suspend(std::coroutine_handle<struct promise<other_t>> h) const noexcept
+    {
+        h.promise().precursor = *this;
+    }
+
+    template<typename result_t> std::optional<result_t> task<result_t>::operator()() noexcept
+    {
+        if (!handle::operator bool())
+            return {};
+        if (!handle::done()) {
+            auto &precursor = handle::promise().precursor;
+            if (precursor) {
+                if (!precursor.done())
+                    precursor.resume();
+                if (precursor.done())
+                    precursor = nullptr;
+            }
+            if (!precursor)
+                handle::resume();
+        }
+        if (handle::done()) {
+            auto x = await_resume();
+            handle::operator=(nullptr);
+            return std::move(x);
+        }
+        return {};
+    }
+
+    inline void task<void>::await_resume() const noexcept
+    {
+        handle::destroy();
+    }
+
+    template<typename other_t> void task<void>::await_suspend(std::coroutine_handle<struct promise<other_t>> h) const noexcept
+    {
+        h.promise().precursor = *this;
+    }
+
+    inline bool task<void>::operator()() noexcept
+    {
+        if (!handle::operator bool())
+            return true;
+        if (!handle::done()) {
+            auto &precursor = handle::promise().precursor;
+            if (precursor) {
+                if (!precursor.done())
+                    precursor.resume();
+                if (precursor.done())
+                    precursor = nullptr;
+            }
+            if (!precursor)
+                handle::resume();
+        }
+        if (handle::done()) {
+            await_resume();
+            handle::operator=(nullptr);
+            return true;
+        }
+        return false;
+    }
+
+}
-- 
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