1 files changed, 75 insertions, 0 deletions
diff --git a/source/executor.cpp b/source/executor.cpp
new file mode 100644
index 0000000..d86abed
--- /dev/null
+++ b/source/executor.cpp
@@ -0,0 +1,75 @@
+// sprit-forth: A portable subroutine-threaded Forth.
+// Copyright (C) 2024  Clyne Sullivan <clyne@bitgloo.com>
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Library General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or (at your
+// option) any later version.
+//
+// This library is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE.  See the GNU Library General Public License for
+// more details.
+//
+// You should have received a copy of the GNU Library General Public License
+// along with this library; if not, write to the Free Software Foundation, Inc.,
+// 51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
+
+#include "executor.hpp"
+
+Executor Exec;
+
+Error Executor::executor(FuncList *list) noexcept
+{
+    auto result = static_cast<Error>(setjmp(jmpbuf));
+    FuncList body;
+
+    if (static_cast<int>(result) == 0) {
+        result = Error::none;
+
+        // We are given the pointer to a list of function pointers.
+        // Dereference once to retrieve the function pointer list.
+        // We do not work with IP initially since it needs to be set to zero if
+        // this is a top-level call/execution.
+        body = *list;
+
+        // Enter the execution loop.
+        goto entry;
+
+        // Execution continues so long as IP is not zero.
+        // If this is a top-level execution of a pre-defined word, then IP will
+        // remain zero'd and the loop will immediately exit.
+        // If this is a defined word's execution, then its "call" will overwrite
+        // IP (and push the initial zero-IP to the return stack); execution will
+        // continue until we return to the zero-IP.
+        while (ip) {
+            // Retrieve next function pointer list.
+            body = (FuncList)*++ip;
+entry:
+            // Dereference `body` to get the first function in the list.
+            // This is casted to take a FuncList as an argument since defined
+            // words need to know their addresses so that they can perform
+            // their "calls".
+            // If the word is pre-defined then the argument will simply be
+            // ignored.
+            auto func = (void (*)(FuncList))*body;
+            func(body);
+        }
+    }
+
+    return result;
+}
+
+Error Executor::execute1(Word *word) noexcept
+{
+    // IP must initially be zero if executing a word at the top level.
+    ip = nullptr;
+    return executor(&word->list);
+}
+
+[[noreturn]]
+void Executor::terminate(Error error) noexcept
+{
+    std::longjmp(jmpbuf, static_cast<int>(error));
+}
+