Assignment 5 Global Variables and Separate Compilation

Computing Machinery I
Assignment 5

Global Variables and Separate Compilation

Reverse Polish (or postfix) notation can be used to represent arithmetic expressions. For example, the infix expression

(1 - 2) * (4 + 5) =

is the following using reverse Polish notation:

1 2 - 4 5 + * =

Hewlett-Packard calculators often use this form of entry. The following is a C program that emulates such a calculator:


#include <stdio.h
#include <stdlib.h

/* Constants */
#define MAXOP 20
#define NUMBER '0'
#define TOOBIG '9'

/* Function prototypes */
int push(int f);
int pop();
void clear();
int getop(char *s, int lim);
int getch();
void ungetch(int c);

int main()
{
int type;
char s[MAXOP];
int op2;

while ((type = getop(s, MAXOP)) != EOF) {
switch (type) {
case NUMBER:
push(atoi(s));
break;
case '+':
push(pop() + pop());
break;
case '*':
push(pop() * pop());
break;
case '-':
op2 = pop();
push(pop() - op2);
break;
case '/':
op2 = pop();
if (op2 != 0)
push(pop() / op2);
else
printf("zero divisor popped\n");
break;
case '=':
printf("\n%d\n\n", push(pop()));
break;
case 'c':
clear();
break;
case TOOBIG:
printf("%.20s ... is too long\n", s);
break;
default:
printf("unknown command %c\n", type);
break;
}
}

return 0;
}


#define MAXVAL 100

int sp = 0;
int val[MAXVAL];

int push(int f)
{
if (sp < MAXVAL)
return val[sp++] = f;
else {
printf("error: stack full\n");
clear();
return 0;
}
}

int pop()
{
if (sp 0)
return val[--sp];
else {
printf("error: stack empty\n");
clear();
return 0;
}
}

void clear()
{
sp = 0;
}

int getop(char *s, int lim)
{
int i, c;

while ((c = getch()) == ' ' || c == '\t' || c == '\n')
;

if (c < '0' || c '9')
return c;

s[0] = c;
for (i = 1; (c = getchar()) = '0' && c <= '9'; i++)
if (i < lim)
s[i] = c;

if (i < lim) {
ungetch(c);
s[i] = '\0';
return NUMBER;
} else {
while (c != '\n' && c != EOF)
c = getchar();
s[lim-1] = '\0';
return TOOBIG;
}
}

#define BUFSIZE 100

char buf[BUFSIZE];
int bufp = 0;

int getch()
{
return bufp 0 ? buf[--bufp] : getchar();
}

void ungetch(int c)
{
if (bufp BUFSIZE)
printf("ungetch: too many characters\n");
else
buf[bufp++] = c;
}

Translate all functions except main() into ARMv8 assembly language, and put them into a separate assembly source code file called a5.asm. These functions will be called from the main() function given above, which will be in its own C source code file called a5Main.c. Also move the global variables into a5.asm. Your assembly functions will call the library routines printf() and getchar(). Be sure to handle the global variables and format strings in the appropriate way. Input will come from standard input; the program is terminated by typing control-d. Run the program to show that it is working as expected, capturing its output using the script UNIX command, and name the output file script.txt. Use a variety of input expressions to show that your program is calculating correctly.

New Skills need for this Assignment:

• Understanding and use of external variables in assembly
• Separate compilation
• Calling assembly functions from main()
• Calling library functions from assembly routines

Submit the following:

1. Your source code and script via electronic submission. Use the Assignment 5 Dropbox Folder in D2L to submit electronically. Your TA will assemble and run your programs to test them. Name your files a5Main.c and a5.asm, and the script as script.txt.

Computing Machinery I
Assignment 5 Grading


Student:__________________________________________


Functionality:

Correct use of external variable(s) 4 ______

push() function in assembly 4 ______

pop() function in assembly 4 ______

clear() function in assembly 2 ______

getop() function in assembly 6 ______

getch() function in assembly 3 ______

ungetch() function in assembly 3 ______

Linking of separate source code modules 2 ______

Correct evaluation of expressions 4 ______

Script showing I/O 2 ______

Complete documentation and commenting 4 ______

Formatting (use of columns and white space) 4 ______

Design quality 4 ______


Total 46 ______ _____%