Due Monday Nov 6, 2000, in class
Add conditional assembly to the assembler for the example assembly language. You may start with either your solution to machine problem 3 or the solution distributed on the web. You should support the IF, ELSE and ENDIF directives discussed in Chapter 6 (see Figures 6.3 and 6.4). You should interpret nonzero values as logically true, and zero as logically false, and you should extend the grammar of expressions so that:
<expression> ::= <relation> { (& | |) <relation> }
<relation> ::= <simple expr> { (> | < | =) <simple expr> }
<simple expr> ::= <term> { (+ | -) <term> }
This extension to the grammar for expressions is, of course, a simple extension
of the pattern you should already have solved for terms and factors, so other
than a few new lines of code, it should be fairly easy.
Note that the and ( & ) and or ( | ) operators should operate on bit patterns; that is, they should not use the "short circuit" forms! The comparison operators ( > < = ) should return 1 for true and 0 for false, as in C. Note that the annoying == notation of C has been abandoned.
Note: The product, as it stands, stinks! The spec does not ask you to provide a "not equals" operator, it does not ask for a "not" unary operator, and it does not ask for an arithmetic negation operator. So, you have to say 0-1 when you mean -1. We'll leave these shortcomings of the assembler for some future class to fix.