CSC231 Homework Solutions 2017

--D. Thiebaut (talk) 17:57, 22 April 2017 (EDT)

---

Problem 1

;;; mystery.asm 
;;; D. Thiebaut  
;;;                
;;; To assemble, link, and run:  
;;;     nasm -f elf  mystery.asm  
;;;     ld -melf_i386 -o mystery mystery.o 
;;;     ./mystery        
;;;      

                section .data
Hello           db      "Hello there!", 10, 10
HelloLen        equ     $-Hello
	
                section .text
                global  _start
_start:

;;; print Hello and a space after it
	
                mov     eax, 4          ; write    
                mov     ebx, 1          ; stdout  
                mov     ecx, Hello      ; address of message to print    
                mov     edx, 6          ; print only 6 chars
                int     0x80

;;; print ! and two line feed chars

                mov     eax, 4          ; write    
                mov     ebx, 1          ; stdout  
                mov     ecx, Hello+11   ; address of ! char
                mov     edx, 3          ; print only 3 chars
                int     0x80

;;; exit                                                                                                                                    
                mov     ebx, 0
                mov     eax, 1
                int     0x80

hw1.asm

;;; hw1.asm
;;; D. Thiebaut  
;;;                
;;; To assemble, link, and run:  
;;;     nasm -f elf  hw1.asm  
;;;     ld -melf_i386 -o hw1 hw1.o 
;;;     ./hw1        
;;;      

                section .data
msg             db      "  CSC231 Assembly "
linefeed	db	10
dashline        db	"------------------"
lineLen		equ	$-dashline
	
                section .text
                global  _start
_start:

;;; print message                                                                                                                           
                mov     eax, 4          ; write    
                mov     ebx, 1          ; stdout  
                mov     ecx, dashline   ; address of message to print    
                mov     edx, lineLen   	; # of chars to print  
                int     0x80

                mov     eax, 4          ; write    
                mov     ebx, 1          ; stdout  
                mov     ecx, dashline   ; address of message to print    
                mov     edx, lineLen   	; # of chars to print  
                int     0x80

		mov	eax, 4		;print line-feed
		mov	ebx, 1
		mov	ecx, linefeed
		mov	edx, 1
		int	0x80

                mov     eax, 4		; write ----
		mov     ebx, 1 		; stdout
		mov     ecx, dashline 	; address of message to print
		mov     edx, 9  	; # of chars to print
		int     0x80

                mov     eax, 4          ; write message
                mov     ebx, 1          ; stdout  
                mov     ecx, msg 	; address of message to print    
                mov     edx, lineLen    ; # of chars to print  
                int     0x80
	
                mov     eax, 4		; write ----
		mov     ebx, 1 		; stdout
		mov     ecx, dashline 	; address of message to print
		mov     edx, 9  	; # of chars to print
		int     0x80

		mov	eax, 4		;print line-feed
		mov	ebx, 1
		mov	ecx, linefeed
		mov	edx, 1
		int	0x80

                mov     eax, 4          ; write    
                mov     ebx, 1          ; stdout  
                mov     ecx, dashline   ; address of message to print    
                mov     edx, lineLen   	; # of chars to print  
                int     0x80

                mov     eax, 4          ; write    
                mov     ebx, 1          ; stdout  
                mov     ecx, dashline   ; address of message to print    
                mov     edx, lineLen   	; # of chars to print  
                int     0x80

		mov	eax, 4		;print line-feed
		mov	ebx, 1
		mov	ecx, linefeed
		mov	edx, 1
		int	0x80

;;; exit                                                                                                                                    
                mov     ebx, 0
                mov     eax, 1
                int     0x80

hw2.asm

;;; ; ; hw2sol.asm
;;; ; ; D. Thiebaut
;;; ; ;
;;; ; ;


	        extern  _printDec
	        extern  _printString
	        extern  _println
	        extern  _getInput
	
	section	.data
prompt		db	"> "
promptLen	equ	$-prompt	
ansStr          db      "ans = "
ansStrLen	equ	$-ansStr	

a		dd	0
b		dd	0
c		dd	0
ans		dd	0
	
		section	.text
		global	_start
_start:
	;; display prompt
		mov	ecx, prompt
		mov	edx, promptLen
		call	_printString
	;; get a
		call	_getInput
		mov	dword[a], eax

	;; display prompt
		mov	ecx, prompt
		mov	edx, promptLen
		call	_printString
	;; get b
		call	_getInput
		mov	dword[b], eax
	
	;; display prompt
		mov	ecx, prompt
		mov	edx, promptLen
		call	_printString
	;; get c
		call	_getInput
		mov	dword[c], eax
	
	;; -----------------------------------
	;; computation: ans = 2*(a-b) + 3*c
	;; -----------------------------------
	
	; your code will go here...
	

	;; -----------------------------------
	;; display "ans ="
	;; -----------------------------------
		mov	ecx, ansStr
		mov	edx, ansStrLen
		call	_printString

	;; -----------------------------------
	;; display ans variable
	;; -----------------------------------
		mov	eax, dword[ans]
		call	_printDec
		call	_println
		call	_println
	
;;; exit
		mov	ebx, 0
		mov	eax, 1
		int     0x80

Teller.asm

;;; ; teller.asm
;;; ; D. Thiebaut
;;; ;
;;; ; Demo of a teller machine program.
;;; ; To assemble, link, and run:
;;; ;     nasm -f elf  teller.asm
;;; ;     ld -melf_i386 -o teller teller.o 231Lib.o
;;; ;     ./teller
;;; ;                

;;;  extern functions that will be linked to this program
;;; ; contained in 231Lib.asm

extern  _printDec
extern  _printString
extern  _println
extern  _getInput

;;; ------------------------------------------------------
;;; DATA SECTION
;;; ------------------------------------------------------        
                section .data
amount          dd      139
no20s           dd      0
no10s           dd      0
no5s            dd      0
no1s            dd      0

msg             db      "amount? "
MSGLEN          equ     $-msg        

;;; ------------------------------------------------------
;;; CODE SECTION
;;; ------------------------------------------------------        
                section .text
                global  _start
        
_start: 

;;; get amount from the user
                mov     ecx, msg
                mov     edx, MSGLEN
                call    _printString
                call    _getInput
                mov     dword[amount], eax
        	call	_println
	
;;; Break down amount in 20s, 10s, 5s, and 1s
                mov     eax, dword[amount]
                mov     edx, 0

                mov     ebx, 20
                mov     eax, dword[amount]
                call    break
                mov     dword[no20s], eax

                mov     ebx, 10
                mov     eax, dword[amount]
                call    break
                mov     dword[no10s], eax
        
                mov     ebx, 5
                mov     eax, dword[amount]
                call    break
                mov     dword[no5s], eax
                mov     eax, dword[amount]
                mov     dword[no1s], eax

                mov     eax, dword[no20s]
                call    _printDec
                call    _println
                mov     eax, dword[no10s]
                call    _printDec
                call    _println
                mov     eax, dword[no5s]
                call    _printDec
                call    _println
                mov     eax, dword[no1s]
                call    _printDec
                call    _println
        

;;; exit
                mov     ebx, 0
                mov     eax, 1
                int     0x80

;;; sum: gets 2 ints in eax and ebx and returns the sum in
;;; eax.
sum:            add     eax, ebx,
                ret

;;; break: gets amount in eax, divider in ebx, divides,
;;; and puts remainder in [amount] and quotient in eax
break:          mov     edx, 0
                div     ebx
                mov     dword[amount], edx
                ret

hw5_1.asm

;;; ; hw5_1.asm
;;; ; D. Thiebaut
;;; ;
;;; ; Prints 10 lines of Pascal triangle.
;;; ;
;;; ; to assemble and run:
;;; ;
;;; ;     nasm -f elf -F  stabs hw5_1.asm
;;; ;     ld -melf_i386 -o hw5_1 hw5_1.o
;;; ;     ./hw5_1
;;; ; -------------------------------------------------------------------

extern		_printString
extern		_getInput
extern		_println
	
;;;  ------------------------------------------------------------
;;;  data areas
;;;  ------------------------------------------------------------

	        section .data
prompt 		db 	"> "
stars 		db 	"******************************************"
N		dd	0
saveECX 	dd	0

;;;  ------------------------------------------------------------
;;;  code area
;;;  ------------------------------------------------------------

	        section .text
	        global  _start

_start:
;;; get N from user
		mov	ecx, prompt
		mov	edx, 2
		call	_printString
		call	_getInput
		mov	dword[N], eax
;;; -------------------------------------------------
;;; print opening triangle
		mov	ecx, dword[N]
for0:		mov	dword[saveECX], ecx

		mov	edx, dword[N]
		sub	edx, ecx
		inc	edx
		mov	ecx, stars
		call    _printString
		call	_println

		mov	ecx, dword[saveECX]
		loop	for0

;;; -------------------------------------------------
;;; print square
		mov	ecx, dword[N]
for1:		mov	dword[saveECX], ecx

;;; print a line of N stars
		mov	ecx, stars
		mov	edx, dword[N]
		call	_printString
		call	_println
	
		mov	ecx, dword[saveECX]
		loop 	for1

;;; -------------------------------------------------
;;; print closing triangle
		mov	ecx, dword[N]
for2:		mov	dword[saveECX], ecx

		mov	edx, ecx
		mov	ecx, stars
		call    _printString
		call	_println

		mov	ecx, dword[saveECX]
		loop	for2
	
;;;  exit()

	        mov     eax,1
	        mov     ebx,0
	        int     0x80	; final system call

hw5_2.sh

#! /bin/bash
# hw5_2.sh
# D. Thiebaut
# gets a number of the command line and prints a triangle
# a square and a triangle with the width equal to the value
# of the number.

N=$1

for i in $( seq 1 $N ) ; do
   for j in $( seq 1 $i ) ; do
      echo -n "*"
   done
   echo ""
done

for i in $( seq 1 $N ) ;do
    for j in $( seq 1 $N ) ; do
      echo -n "*"
   done
   echo""
done

exit

for i in $( seq 1 $N ) ;do
    top=$( expr $N - $i + 1 )
    for j in $( seq 1 $top ) ; do
      echo -n "*"
   done
   echo""
done

GameOfLife.asm

;;; ; GameOfLife.asm
;;; ; Authors: D. Thiebaut and CSC231 Class
;;; ;
;;; ; Implements a 1-dimensional version of 
;;; ; Conway's Game of life.
;;; ; Note that because we do not "know" yet
;;; ; how to test or to use functions, the code
;;; ; is not as efficient as it could be.
;;; ;
;;; ; to assemble and run:
;;; ;
;;; ;     nasm -f elf -F  stabs GameOfLife.asm
;;; ;     ld -melf_i386 -o GameOfLife GameOfLife.o
;;; ;     ./GameOfLife
;;; ; -------------------------------------------------------------------


;;;  ------------------------------------------------------------
;;;  data areas
;;;  ------------------------------------------------------------

	        section .data
;;; the current dish with its cells.  We use 0 and 1 to
;;; indicate dead and live cells, respectively.
%include	"dishArray.inc"

;;; the new generation of cells.  That's the "future" of the
;;; cells in the dish.  We make it the same size as dish, and
;;; fill it with N dead cells.
	
newGen	        times   N db 0
	
;;; dishP is a string that will contain ' ' or '!' for
;;; each 0 or 1 in dish.  
dishP		times   N  db ' '
		db	10			; add a \n at the end
						;  of dishP
	
generation	dd	0			; save ecx from for generation loop
i		dd	0			; used by for loops
	
;;;  ------------------------------------------------------------
;;;  code area
;;;  ------------------------------------------------------------

	        section .text
	        global  _start

_start:
main:	
;;; -------------------------------------------------------------
;;; print( dish )
		;; first we copy dish into dishP and at the same
		;; time replace 0 by ' ' and 1 by '!'

;;; for i in range( N ):
		mov	esi, dish 
		mov	edi, dishP

		mov	dword[i], 0
forPrint:	cmp	dword[i], N
		jge	forPrintEnd
	
		mov	al, byte[esi]
		add	al, ' '			;0 becomes ' ', 1 becomes '!'
		mov	byte[edi], al
		inc	esi			;esi points to next byte in dish
		inc	edi			;edi points to next byte in dispP

		;; i++, loop back
		inc	dword[i]
		jmp	forPrint
forPrintEnd:	
	
		;; print dishP as a string.
		mov	eax, 4			;prints dishP to screen
		mov	ebx, 1
		mov	ecx, dishP 		;dishP address
		mov	edx, N+1		;+1 to include the \n
		int	0x80


;;; -----------------------------------------------------------
;;; for generation in range( maxGen ):

		mov	dword[generation], 0
	

forGen:		mov	eax, dword[generation]
		cmp	eax, dword[maxGen]
		jge	forGenEnd
	

;;; -----------------------------------------------------------
;;;      newGen = life( dish, N )
;;; 	 newGen[0] = 0
;;; 	 newGen[N-1] = 0

	        mov    byte[newGen], 0
		mov    byte[newGen+N-1], 0

;;; -----------------------------------------------------------
;;;      for i in range( 0, N ):

		mov	esi, dish
		mov	edi, newGen
	
		mov    	dword[i], 0
	
forLife:	cmp	dword[i], N
		jge  	forLifeEnd
	
;;; -----------------------------------------------------------
;;; 	     fate = dish[i-1] ^ dish[i+1]
;;; 	     newGen[i] = fate
		mov	al, byte[esi-1]
	        xor     al, byte[esi+1]
	        mov	byte[edi], al
		inc	esi
		inc	edi

		inc	dword[i]
		jmp	forLife
forLifeEnd:
	
;;; -----------------------------------------------------------
;;;     dish = newGen

		mov	dword[i],0
		mov	esi, newGen
		mov	edi, dish
		
forMove:	cmp	dword[i], N
		jge	forMoveEnd
	
		mov	al, byte[esi] 	;copy newGen[i] to dish[i]
		mov	byte[edi], al
		inc	esi
		inc	edi

		inc	dword[i]
		loop	forMove
forMoveEnd:
;;; -------------------------------------------------------------
;;; print( dish )
		;; first we copy dish into dishP and at the same
		;; time replace 0 by ' ' and 1 by '!'

;;; for i in range( N ):
		mov	esi, dish 
		mov	edi, dishP

		mov	dword[i], 0
forPrint2:	cmp	dword[i], N
		jge	forPrintEnd2
	
		mov	al, byte[esi]
		add	al, ' '			;0 becomes ' ', 1 becomes '!'
		mov	byte[edi], al
		inc	esi			;esi points to next byte in dish
		inc	edi			;edi points to next byte in dispP
		inc	dword[i]
		jmp	forPrint2
forPrintEnd2:
	
		;; print dishP as a string.
		mov	eax, 4			;prints dishP to screen
		mov	ebx, 1
		mov	ecx, dishP 		;dishP address
		mov	edx, N+1		;+1 to include the \n
		int	0x80

;;; ready to loop back to forGen
		inc	dword[generation]
		jmp	forGen
forGenEnd:
	
;;;  exit()

exit:		mov     eax,1
	        mov     ebx,0
	        int     0x80	; final system call

hw7_1.C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main( int argc, char *argv[] ) {
  int n, i, name;
  char sentence[100];
  char stars[100];

  if ( argc < 2 ) {
    printf( "Syntax: %s string [string...]\n", argv[0] );
    exit( 1 );
  }

  strcpy( sentence, "* " );
  for ( i = 1; i < argc; i++ ) {
    if ( i > 1 )
       strcat( sentence, " " );
    strcat( sentence, argv[i] );
  }
  strcat( sentence, " *" );

  // printf( "%s\n", sentence );

  n = (int) strlen( sentence );

  strcpy( stars, "*" );
  for ( i=0; i<strlen( stars)-1; i++ )
    strcat( stars, "*" );

  for ( i=0; i< n-1; i++ ) {
    stars[i+1] = '\0';
    printf( "%s\n", stars );
    stars[i+1] = '*';
  }

  printf( "%s\n", sentence );

  for ( i=n-2; i>= 0; i-- ) {
    stars[i+1] = '\0';
    printf( "%s\n", stars );
    stars[i+1] = '*';
  }


  return 0;
}

hw7_2.asm

;;; ; -------------------------------------------------------------------
;;; ; hw4b.asm
;;; ; Julia Burch
;;; ; 231a-aa
;;; ;
;;; ; Computes and prints the first 10 rows of Pascal's triangle.
;;; ; OUTPUT:
;;; ;  1        0       0       0       0       0       0       0       0       0
;;; ;  1        1       0       0       0       0       0       0       0       0
;;; ;  1        2       1       0       0       0       0       0       0       0
;;; ;  1        3       3       1       0       0       0       0       0       0
;;; ;  1        4       6       4       1       0       0       0       0       0
;;; ;  1        5       10      10      5       1       0       0       0       0
;;; ;  1        6       15      20      15      6       1       0       0       0
;;; ;  1        7       21      35      35      21      7       1       0       0
;;; ;  1        8       28      56      70      56      28      8       1       0
;;; ;  1        9       36      84      126     126     84      36      9       1
;;; ; to assemble and run:
;;; ;
;;; ;     nasm -f elf -F  stabs hw4b.asm
;;; ;     gcc -o hw4b driver.c asm_io.o hw4b.o
;;; ;     ./hw4b
;;; ; -------------------------------------------------------------------

        ;; %include files here...
extern	_printDec
extern  _println	
extern  _printString
	
;;;  ------------------------------------------------------------
;;;  data areas
;;;  ------------------------------------------------------------

        section .data

        shift    db     0
        pascal   db     1, 0, 0, 0, 0, 0, 0, 0, 0, 0
        temp     dd     0
        space    db     9
        rows     equ    10
;;;  ------------------------------------------------------------
;;;  code area
;;;  ------------------------------------------------------------

        section .text
        global  _start

_start:	

        ;; move first line of Pascal into edi, then rows into ecx
        ;; to initialize and run for loop 10 times.
        mov     edi, pascal
        mov     ecx, rows
main:
        ;; store ecx in a temporary variable, move rows into ecx to initialize
        ;; and run print_triangle loop. Move the first line into edi
        ;; and 0 into esi.
        push	ecx
        mov     ecx, rows
        mov     edi, pascal
        mov     esi, 0

print_triangle:
        ;; print the int in al, print tab and then clear
        ;; tab from register.
	push	ecx
        mov     al, byte[edi+esi]
        call    _printDec
	
        mov     ecx, space
	mov     edx, 1
        call    _printString
	
        mov     eax, 0
        inc     esi

	pop	ecx
        loop print_triangle

        ;; print a new line
        call    _println

        ;; load newly calculated pascal line into edi, then shift the row
        mov     edi, pascal
        mov     esi, shift
        mov     ecx, rows-1

calculate:
        ;; move pascal digit into al, add it to previous row's, store the value
        mov     al, byte[edi+ecx]
        add     al, byte[esi+ecx]
        mov     byte[edi+ecx], al

        loop calculate

        ;; restore value of ecx for loop
	pop	ecx
        loop 	main

;;;  exit()
        mov	ebx, 0
	mov	eax, 1
	int	0x80

hw7_3.asm (mystery program)

;;; helloWorld.asm 
;;; D. Thiebaut  
;;;                
;;; To assemble, link, and run:  
;;;     nasm -f elf  helloWorld.asm  
;;;     ld -melf_i386 -o helloWorld helloWorld.o 
;;;     ./helloWorld        
;;;      

                section .data
		db	"Mystery", 0
msg1		db      "Vive le chacalot au lait!", 0
msg2            db      "Assembly is fun!", 0
msg3		db	0x01, 0x02, 0x03
x		dd	128
y		dd	64
HelloLen        equ     $-msg1
	
                section .text

_mystery:	

;;; print message
        	add	byte[msg1+10],'o'-'a'
		add	byte[msg1+12],'o'-'a'
		add	byte[msg1+14],'a'-'o'
                mov     eax, 4          ; write    
                mov     ebx, 1          ; stdout  
                mov     ecx, msg1+8
                mov     edx, 8          ; # of chars to print  
                int     0x80

		mov	eax, dword[x]
		add	eax, 0xFFFFFFFF
		xor	ebx, ebx
		mov	bx, word[y]
		shl	bx,16
		mov	edx, 0x12345678
		mov	dx, ax
		mov	ecx, 10
		loop	there
there:		
		
;;; exit                                                                                                                                    
                mov     ebx, 0
                mov     eax, 1
                int     0x80

hw8_1.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


void main( int argc, char *argv[] ) {
  char *marker1, *marker2, *DNA;
  char *fileName;

  if (argc < 4 ) {
    printf( "syntax: %s marker1 marker2 DNA\n", argv[0] );
    return;
  }

  marker1 = argv[1];
  marker2 = argv[2];
  DNA     = argv[3];
  
  //--- print the markers and DNA ---
  /* (for debugging purposes)
  printf( "Marker1 = %s\n", marker1 );
  printf( "Marker2 = %s\n", marker2 );
  if ( strlen( DNA ) > 80 )
    printf( "DNA     = %.*s...%s (%d bases)\n\n",
          10, DNA, DNA+((int)strlen(DNA)-10), 
	  (int) strlen( DNA) );
  else
    printf( "DNA     = %s\n\n", DNA );
  */

  //--- add your code below this point ---
  char *first, *second;
  first = strstr( DNA, marker1 );
  if ( first == NULL ) {
    printf( "%s\n", DNA );
    return;
  }
  second = strstr( first+1, marker2 );
  if ( second == NULL ) {
    printf( "%s\n", DNA );
    return;
  }
  
  char *p;
  for ( p= first; p < second+strlen(marker2); p++ ) 
     *p = '-';

  printf( "%s\n", DNA );
}

hw8_2.asm

; hw8_2.asm
; D. Thiebaut

	global 	f1
	global	f2
	global	f3

;;; ------------------------------------------------------
;;; f1( s ): modifies s in place and make it uppercase.
f1:	push	ebp
	mov	ebp, esp
	push	ebx
	mov	ebx, dword[ebp+8]
.for:	cmp	byte[ebx], 0
	je	.done
	cmp	byte[ebx],'a'
	jl	.endfor
	cmp	byte[ebx],'z'
	jg	.endfor
	add	byte[ebx],'A'-'a'
.endfor:
	inc	ebx
	jmp	.for
.done:
	pop	ebx
	pop	ebp
	ret	4

;;; ------------------------------------------------------
;;; f2( a, b, c )
;;; returns 2a + 3b -c in eax
;;; computes it as 2(a+b) + b - c (fewer operations)
f2:	push	ebp
	mov	ebp, esp
	mov	eax, dword[ebp+8+4+4] ; get first param
	add	eax, dword[ebp+8+4]   ; eax <- a+b
	add	eax, eax	      ; eax <- 2(a+b)
	add	eax, dword[ebp+8+4]   ; eax <- 2(a+b) + b
	sub	eax, dword[ebp+8]     ; eax <- 2a + 3b -c
	pop	ebp		      ;
	ret	4*3		      ; return and get rid of 3 ints


;;; ------------------------------------------------------
;;; f3( array, n )
;;; computes the number of even ints in array, of length n.
;;; returns this number in eax.
f3:	push	ebp
	mov	ebp, esp
	
;;; 	push	ebx
	push	ecx
	
	mov	ebx, dword[ebp+8+4] 	; ebx <- array
	mov	ecx, dword[ebp+8]	; ecx <- n
	mov	eax, 0			; number of even ints
.for:	and	dword[ebx], 1		; and array[i] with 1
	jnz	.notEven		; if result is 1, then odd number
.even:	inc	eax			; otherwise, add 1 to counter.
.notEven:
	add	ebx, 4
	loop	.for

;;; 	pop	ecx
	pop	ebx
	
	pop	ebp
	ret	2*4

...