COMP1521 2022T3 Q8 — MIPS functions & recursion

COMP1521 2022T3 Q8 · 10 marks · MIPS Topic: MIPS functions & recursion · Source: https://cgi.cse.unsw.edu.au/~cs1521/26T1/resources/practice_exams.html

Summary: Evaluate a boolean expression via recursive descent

You have been given 22t3final_q8.s , a MIPS assembler program that reads a line of input and then prints 'T' on a new line.

Add code to 22t3final_q8.s to make it equivalent to this C program:

// // // // // // // // DO NOT CHANGE THIS FILE! // // // // // // // // // COMP1521 22T3 ... final exam, question 8 // Modify 22t3final_q8.s so that its behaviour // matches the following C code.

#include <stdio.h>

char * s ;

int expression ( void ); int term ( void ); int value ( void );

int main ( void ) { char buffer [ 10000 ]; fgets ( buffer , 10000 , stdin ); s = buffer ;

if ( expression ()) { printf ( "T \n " ); } else { printf ( "F \n " ); }

return 0 ; }

int expression ( void ) { int lhs = term (); if ( * s != '|' ) { return lhs ; } s ++ ; int rhs = expression (); return lhs || rhs ; }

int term ( void ) { int lhs = value (); if ( * s != '&' ) { return lhs ; } s ++ ; int rhs = term (); return lhs && rhs ; }

int value ( void ) { int retval = * s == 'T' ; s ++ ; return retval ; }

The above C program reads a line of input containing a boolean expression, and evaluates it.

The boolean expression only contains the characters 'T', 'F', representing true and false respectively, and the operators '&' and '|', representing the logical AND and OR operators.

For example:

1521 mipsy 22t3final_q8.s T&F F 1521 mipsy 22t3final_q8.s T|F T 1521 mipsy 22t3final_q8.s F|T&F F

No error checking is required.

Your program can assume it is given exactly one line of input.

Your program can assume this line contains only these 4 characters: TF&|

You can assume the line contains less than 10,000 characters.

Your program can assume that these characters form a valid boolean expression.

Your solution must be in MIPS assembler only.

🤖 Write MIPS (mipsy). Read one line — a boolean expression over T F & | (&=AND, |=OR; | binds looser; both right-associative, exactly per the exam's recursive-descent C). Print T or F.

Verified on the sandbox AND cross-checked against an independent oracle.