Boost C++ Libraries

libs/spirit/example/qi/compiler_tutorial/mini_c/vm.cpp

/*=============================================================================
    Copyright (c) 2001-2011 Joel de Guzman

    Distributed under the Boost Software License, Version 1.0. (See accompanying
    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
=============================================================================*/
#include "vm.hpp"

#if defined(_MSC_VER)
# pragma warning(disable: 4800) // forcing value to bool 'true' or 'false'
                                // (performance warning)
#endif

namespace client
{
    int vmachine::execute(
        std::vector<int> const& code
      , std::vector<int>::const_iterator pc
      , std::vector<int>::iterator frame_ptr
    )
    {
        std::vector<int>::iterator stack_ptr = frame_ptr;

        while (true)
        {
            switch (*pc++)
            {
                case op_neg:
                    stack_ptr[-1] = -stack_ptr[-1];
                    break;

                case op_not:
                    stack_ptr[-1] = !bool(stack_ptr[-1]);
                    break;

                case op_add:
                    --stack_ptr;
                    stack_ptr[-1] += stack_ptr[0];
                    break;

                case op_sub:
                    --stack_ptr;
                    stack_ptr[-1] -= stack_ptr[0];
                    break;

                case op_mul:
                    --stack_ptr;
                    stack_ptr[-1] *= stack_ptr[0];
                    break;

                case op_div:
                    --stack_ptr;
                    stack_ptr[-1] /= stack_ptr[0];
                    break;

                case op_eq:
                    --stack_ptr;
                    stack_ptr[-1] = bool(stack_ptr[-1] == stack_ptr[0]);
                    break;

                case op_neq:
                    --stack_ptr;
                    stack_ptr[-1] = bool(stack_ptr[-1] != stack_ptr[0]);
                    break;

                case op_lt:
                    --stack_ptr;
                    stack_ptr[-1] = bool(stack_ptr[-1] < stack_ptr[0]);
                    break;

                case op_lte:
                    --stack_ptr;
                    stack_ptr[-1] = bool(stack_ptr[-1] <= stack_ptr[0]);
                    break;

                case op_gt:
                    --stack_ptr;
                    stack_ptr[-1] = bool(stack_ptr[-1] > stack_ptr[0]);
                    break;

                case op_gte:
                    --stack_ptr;
                    stack_ptr[-1] = bool(stack_ptr[-1] >= stack_ptr[0]);
                    break;

                case op_and:
                    --stack_ptr;
                    stack_ptr[-1] = bool(stack_ptr[-1]) && bool(stack_ptr[0]);
                    break;

                case op_or:
                    --stack_ptr;
                    stack_ptr[-1] = bool(stack_ptr[-1]) || bool(stack_ptr[0]);
                    break;

                case op_load:
                    *stack_ptr++ = frame_ptr[*pc++];
                    break;

                case op_store:
                    --stack_ptr;
                    frame_ptr[*pc++] = stack_ptr[0];
                    break;

                case op_int:
                    *stack_ptr++ = *pc++;
                    break;

                case op_true:
                    *stack_ptr++ = true;
                    break;

                case op_false:
                    *stack_ptr++ = false;
                    break;

                case op_jump:
                    pc += *pc;
                    break;

                case op_jump_if:
                    if (!bool(stack_ptr[-1]))
                        pc += *pc;
                    else
                        ++pc;
                    --stack_ptr;
                    break;

                case op_stk_adj:
                    stack_ptr += *pc++;
                    break;

                case op_call:
                    {
                        int nargs = *pc++;
                        int jump = *pc++;

                        // a function call is a recursive call to execute
                        int r = execute(
                            code
                          , code.begin() + jump
                          , stack_ptr - nargs
                        );

                        // cleanup after return from function
                        stack_ptr[-nargs] = r;      //  get return value
                        stack_ptr -= (nargs - 1);   //  the stack will now contain
                                                    //  the return value
                    }
                    break;

                case op_return:
                    return stack_ptr[-1];
            }
        }
    }
}