sprit-forth/source/executor.cpp

// 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));
}