MegaProcessor

    local result = opVal[op1];
    if( result == nil ) then
        Error("ADDQ value must be #2, #1, #-1 or #-2");
    end
    return result ;
end

function isShiftOp(b2,offset1,offset2)
--  Evaluate an operand with one of the following formats
--    :  #00..#15
--    :  #-16..#-1
--    :  R0..R3
--
    local result;
    if( b2:sub(1,1 ) == '#' ) then
        if( b2:sub(2,2) == '-' ) 
        then result = 32 - Eval_as_byte(b2:sub(3,-1))[1];  -- TODO, find a more transparent form for this.
        else result = Eval_as_byte(b2:sub(2,-1))[1];
        end
        Check( result, "Evaluation of bitop specifier failed.");
        result = result + offset1;
    else
        result = offset2 + isReg(b2);
    end--match '#'
    return result ;
end

--------------------------------------------------------------------------------
-- Chapter: Evaluate symbol:
--------------------------------------------------------------------------------
require( './lib' );
require( 'symtab' );

--
-- Take a value in range 0..2^32-1 and return a table of byte-values
-- in little-endian order
--

function As_table(val)
    local r = {};

    repeat
        local b = math.fmod(val,256);
        table.insert(r,b);
        val = math.floor(val / 256);
    until( val == 0 );

    return r ;
end

-- 
-- Evaluate a constant expression in any of the formats below
--    Decimal, just digits
--    Hex, prefix 0x or 0X
--    Binary, prefix 0b or '%'
--    String, enclosed in single or double quotes.
--    Symbol, start with underscore or letter, followed by one or more letters/digits/underscores
--
-- Return a table with the bytes that compose the value described object.
-- [==[
function Eval(exp)
    local capture, idx;

    if( exp == '' ) then Error("Empty expression, can't evaluate.") end;
    -- Decimal, just digits.
    capture = exp:match("^(%d+)") 
    if( capture and not exp:match("%D+") ) then return( As_table(tonumber(capture)) ); end;


    -- Hex, prefix 0x or 0X
    capture = exp:match("^(0[xX]%x+)") 

    end--if


    capture = exp:match("^([_%a]+[_%w]*)");
    if( capture ) then
        local result = symtab_lookup(capture);
        if( not result ) then
            Error("Undefined symbol");

        end
        return( As_table( result ) );
    end

    print( exp );
    Error( "Failed to evaluate." );

end--Eval()

function Eval_as_word(exp)
    local t = Eval(exp);
    if( #t == 1 ) then table.insert(t,0x00); end--if : append zero as most-significant byte.
    return t ;
end

function Eval_as_byte(exp)
    local t = Eval(exp);
    if( #t ~= 1 ) then Error("Byte operand expected"); end--if
    return t ;
end

--EOF--

    if( f2:lower() ~= 'ps' ) then
        Error("This instruction is for PS only");
    end
    return 0xf4, 0x00 ; -- TODO
end

function do_ASL(f1, f2, f3)
    local b1 = 0xd8 + isReg(f2);
    local b2 = isShiftOp(f3, 0x40, 0x60);
    return b1, b2 ;
end

function do_ASL_WT(f1, f2, f3)
    local b1 = 0xd8 + isReg(f2);
    local b2 = 0x68 + isReg(f3);
    return b1, b2 ;
end

        else 
            return 0x80 + (ourNr + 2*(ourNr2-2)) ;
        end
    end
end

function do_LSL(f1, f2, f3)
    local b1 = 0xd8 + isReg(f2);
    local b2 = isShiftOp(f3, 0x00, 0x20);
    return b1, b2 ;
end

function do_LSL_WT(f1, f2, f3)
    local b1 = 0xd8 + isReg(f2);
    local b2 = 0x28 + isReg(f3);
    return b1, b2 ;
end

end

function do_RETI(f1, f2, f3)
    return 0xc7 ;
end

function do_ROL(f1, f2, f3)
    local b1 = 0xd8 + isReg(f2);
    local b2 = isShiftOp(f3, 0x80, 0xa0);
    return b1, b2 ;
end

function do_ROL_WT(f1, f2, f3)
    local b1 = 0xd8 + isReg(f2);
    local b2 = 0xa8 + isReg(f3);
    return b1, b2 ;
end

function do_ROR(f1, f2, f3)
    local b1,b2 = 0xd8, 0x00;
    return b1, b2 ; -- TODO
end

function do_ROR_WT(f1, f2, f3)
    local b1 = 0xd8 + isReg(f2);
    local b2 = 0xb8 + isReg(f3);
    return b1, b2 ;
end

function do_ROXL(f1, f2, f3)
    local b1 = 0xd8 + isReg(f2);
    local b2 = isShiftOp(f3, 0xc0, 0xe0);
    return b1, b2 ;
end

function do_ROXL_WT(f1, f2, f3)
    local b1 = 0xd8 + isReg(f2);
    local b2 = 0xe8 + isReg(f3);
    return b1, b2 ;
end