test.cpp

BOOST_AUTO_TEST_CASE( call_and_return_factorial )
{
  auto code = create_code_segment(
    // stack: [-4: n] (supplied by executor)
    opcode::relative_load_stack, std::uint32_t( 4 ), std::int32_t( -4 ),
    // stack: [-8: n (return value memory, to be overwritten)] [-4: n]
    // result = factorial( n )
    opcode::call, label_reference( "factorial" ),
    // stack: [factorial( n )]
    opcode::exit,

    label( "factorial" ),
    // stack: [-12: return_value] [-8: n] [-4: return_address]

    opcode::relative_load_stack, std::uint32_t( 4 ), std::int32_t( -8 ),
    // stack: [-16: return_value] [-12: n] [-8: return_address] [-4: n]

    opcode::push_32, std::int32_t( 1 ),
    // stack: [-20: return_value] [-16: n] [-12: return_address] [-8: n] [-4: 1]

    opcode::less_than_or_equals_i32,
    // stack: [-16: return_value] [-12: n] [-8: return_address] [-4: n <= 1]

    opcode::relative_jump_if_false, label_reference_offset( "n > 1" ),
    // stack: [-12: return_value] [-8: n] [-4: return_address]

    //    n <= 1: return 1
    opcode::push_32, std::int32_t( 1 ),
    // stack: [-16: return_value] [-12: n] [-8: return_address] [-4: 1]
    opcode::relative_jump, label_reference_offset( "return_top_of_stack" ),

    //    n > 1: return n * factorial( n - 1)
    label( "n > 1" ),
    // stack: [-12: return_value] [-8: n] [-4: return_address]
    opcode::reserve, std::uint32_t( 4 ),
    opcode::relative_load_stack, std::uint32_t( 4 ), std::int32_t( -12 ),
    // stack: [-20: return_value] [-16: n] [-12: return_address] [-8: 0] [-4: n]
    opcode::push_32, std::int32_t( 1 ),
    opcode::subtract_i32,
    // stack: [-20: return_value] [-16: n] [-12: return_address] [-8: 0] [-4: n-1]
    opcode::call, label_reference( "factorial" ),
    // stack: [-16: return_value] [-12: n] [-8: return_address] [-4: factorial(n-1)]
    opcode::relative_load_stack, std::uint32_t( 4 ), std::int32_t( -12 ),
    // stack: [-20: return_value] [-16: n] [-12: return_address] [-8: factorial(n-1)] [-4: n]
    opcode::multiply_i32,
    // stack: [-16: return_value] [-12: n] [-8: return_address] [-4: factorial(n-1)*n]

    label( "return_top_of_stack" ),
    opcode::relative_store_stack, std::uint32_t( 4 ), std::int32_t( -16 ), // store result in return_value
    opcode::pop, std::uint32_t( 4 ), // pop result from top of stack
    // stack: [-12: return_value = 1] [-8: n] [-4: return_address]
    opcode::return_, std::uint32_t( 4 ) // return
    );
  perseus::stack result = processor( std::move( code ) ).execute( 0, std::move( perseus::stack().push< std::int32_t >( 5 ) ) );
  BOOST_CHECK_EQUAL( result.pop< std::uint32_t >(), 120 );
  BOOST_CHECK_EQUAL( result.size(), 0 );
}