CSC231 Homework 8 Solution 2012

--D. Thiebaut 12:15, 13 November 2012 (EST)

---

Problem #1, Version 1

This version contains the complete code. Version 2 below separates the dumpRegs functions and main program into two files.

;;; ---------------------------------------------------------
;;; hw8aSol.asm
;;; D. Thiebaut
;;; 11/13/12
;;; This program supports several functions that allow the user
;;; to dump the contents of the main 6 registers (eax, ebx, ecx,
;;; edx, esi and edi) to the screen.  Great for debugging without
;;; a debugger.
;;;
;;; Typical output:
;;; 	+-----------------+
;;; 	| eax = 1234 5678 |
;;; 	| ebx = 55FF 55FF |
;;; 	| ecx = FEDC BA98 |
;;; 	| edx = 0000 0000 |
;;; 	| esi = 1111 2222 |
;;; 	| edi = 2222 3333 |
;;; 	+-----------------+
;;; 	+-----------------+
;;; 	| eax = 1234 5678 |
;;; 	| ebx = 55FF 55FF |
;;; 	| ecx = FEDC BA98 |
;;; 	| edx = 0000 0000 |
;;; 	| esi = 1111 2222 |
;;; 	| edi = 2222 3333 |
;;; 	+-----------------+
;;;
;;; To assemble, link and run:
;;;   nasm -f elf hw8aSol.asm
;;;   ld -melf_i386 hw8aSol.o -o hw8aSol
;;;   ./hw8aSol
;;; ---------------------------------------------------------

		section	.data
hex		db	"0123456789ABCDEF"
regs		db	"axbxcxdxsidi"
line		db	"+-----------------+", 10
string		db	"| exx = .... .... |", 10
lineLen 	equ	$-string
reg		equ	string+3
word1		equ	string+8

		section	.text
		global	_start

_start:

;;; Initialize the registers
		mov	eax, 0x12345678
		mov	ebx, 0x55FF55FF
		mov	ecx, 0xFEDCBA98
		mov	edx, 0x00000000
		mov	esi, 0x11112222
		mov	edi, 0x22223333

;;; dump them twice to verify that no registers gets modified...
	        call    dumpRegs
		call	dumpRegs


;;; exit back to OS
		mov	ebx, 0
		mov	eax, 1
		int	0x80

;;; ---------------------------------------------------------
;;; dumpRegs: dumps the contents of the 6 main registers (eax
;;; ebx, ecx, edx, esi and edi) in a box on the screen.
;;; the screen.  Does not modify any register
;;; ---------------------------------------------------------
dumpRegs:	pushad

;;; put all the registers to print in the stack.  The loop
;;; will pop each one, one at a time, once per loop.
	
		push	edi
		push	esi
		push	edx
		push	ecx
		push	ebx
		push	eax

;;; print top bar
		call	printBar
	
;;; prepare to loop 6 times (6 registers )
		mov	ecx, 6
		mov	esi, 0

.for		pop	ebx			;get value of register to convert from stack
		push	ecx			;save loop counter
		lea	eax, [regs + esi*2]	;get address of string representing register
	
		mov	ax, word [eax] 		;ax gets "ax" or "bx" or "cx" or ... "di"
		mov	word[reg], ax		;modify string with name of register
	
		mov	edx, word1 		;edx points to buffer where to store hex digits
						;ebx contains register to convert
		call 	storeDWord		;store hex equivalent of ebx in string
	
		mov	ecx, string 		;print the whole string
		mov	edx, lineLen
		call	printInt80
		inc	esi			;index into register names incremented
		pop	ecx			;get loop counter back
		loop	.for

;;; print bottom bar
		call 	printBar
	
		popad
		ret

;;; ---------------------------------------------------------
;;; storeDWord: gets
;;; 	ebx: register to convert
;;; 	edx: address where to put information
;;; ---------------------------------------------------------
		
storeDWord:	rol	ebx, 16			;bring most sig word in least sig word
		call	storeWord
	
		inc	edx			;make edx skip space in string
	
		rol	ebx, 16			;get lower byte back in least sig pos
		call	storeWord
		
		ret

;;; ---------------------------------------------------------
;;; storeWord: gets
;;;     bx: word to convert
;;; 	edx: address where to put information. edx incremented by 4
;;; ---------------------------------------------------------
storeWord:	rol	bx, 8			;put most sig byte of bx in lower position
		call	storeByte		;and convert it.  Store it in where edx 
						;points to. 
		rol	bx, 8			;same with lower nybble
		call	storeByte
		ret
	
;;; ---------------------------------------------------------
;;; storeByte: gets
;;;     bl: byte to convert
;;; 	edx: address where to store information.  edx incremented by 2 automatically
;;; ---------------------------------------------------------
storeByte:	push	ebx
		push	eax
	
		rol	bl, 4			;get upper nybble in lower position (LSB)
		mov	al, bl			;play with al now
		and	eax, 0x0000000F		;clear all but the least significant nybble
		add	eax, hex		;get ascii in hex array equivalentn to nybble
		mov	al, [eax] 		;hex digit now in bl
		mov	byte [edx], al		;store ascii in string
		inc	edx

		rol	bl, 4			;get lower nybble back
		mov	al, bl			;play with al
		and	eax, 0x0000000F
		add	eax, hex
		mov	al, [eax]
		mov	byte [edx], al
		inc	edx
	
		pop	eax
		pop	ebx
		ret
		
;;; ---------------------------------------------------------
;;; printInt80: prints on the screen the string whose address
;;; is in ecx and length in edx.
;;; does not modify registers
;;; ---------------------------------------------------------
printInt80:	push	eax
		push	ebx
	
		mov	eax, 4
		mov	ebx, 1
		int	0x80
	
		pop	ebx
		pop	eax
		ret
	
;;; ---------------------------------------------------------
;;; printBar: prints the horizontal bar
;;; does not modify registers
;;; ---------------------------------------------------------
printBar:	push	ecx
		push	edx
	
		mov	ecx, line
		mov	edx, lineLen
		call	printInt80
	
		pop	edx
		pop	ecx
		ret

Problem #1, Version 2

Main Program

;;; ---------------------------------------------------------
;;; hw8aSol2.asm
;;; D. Thiebaut
;;; 11/13/12
;;; This program uses the library dumpRegs.asm to dump 
;;; the contents of the main 6 registers (eax, ebx, ecx,
;;; edx, esi and edi) to the screen.  Great for debugging without
;;; a debugger.
;;;
;;; Typical output:
;;; 	+-----------------+
;;; 	| eax = 1234 5678 |
;;; 	| ebx = 55FF 55FF |
;;; 	| ecx = FEDC BA98 |
;;; 	| edx = 0000 0000 |
;;; 	| esi = 1111 2222 |
;;; 	| edi = 2222 3333 |
;;; 	+-----------------+
;;; 	+-----------------+
;;; 	| eax = 1234 5678 |
;;; 	| ebx = 55FF 55FF |
;;; 	| ecx = FEDC BA98 |
;;; 	| edx = 0000 0000 |
;;; 	| esi = 1111 2222 |
;;; 	| edi = 2222 3333 |
;;; 	+-----------------+
;;;
;;; To assemble, link and run:
;;;   nasm -f elf hw8aSol.asm
;;;   ld -melf_i386 hw8aSol.o -o hw8aSol
;;;   ./hw8aSol
;;; ---------------------------------------------------------

%include "dumpRegs.asm"
	
		section	.text
		global	_start

_start:

;;; Initialize the registers
		mov	eax, 0x12345678
		mov	ebx, 0x55FF55FF
		mov	ecx, 0xFEDCBA98
		mov	edx, 0x00000000
		mov	esi, 0x11112222
		mov	edi, 0x22223333

;;; dump them twice to verify that no registers gets modified...
	        call    dumpRegs
		call	dumpRegs


;;; exit back to OS
		mov	ebx, 0
		mov	eax, 1
		int	0x80

Library

;;; ---------------------------------------------------------
;;; dumpRegs.asm
;;; D. Thiebaut
;;; 11/13/12
;;; This libary supports several functions that allow the user
;;; to dump the contents of the main 6 registers (eax, ebx, ecx,
;;; edx, esi and edi) to the screen.  Great for debugging without
;;; a debugger.
;;;
;;; Typical output:
;;; 	+-----------------+
;;; 	| eax = 1234 5678 |
;;; 	| ebx = 55FF 55FF |
;;; 	| ecx = FEDC BA98 |
;;; 	| edx = 0000 0000 |
;;; 	| esi = 1111 2222 |
;;; 	| edi = 2222 3333 |
;;; 	+-----------------+
;;; Include in program as follows:
;;; 
;;; 
;;; %include "dumpRegs.asm"
;;; ---------------------------------------------------------

		section	.data
hex		db	"0123456789ABCDEF"
regs		db	"axbxcxdxsidi"
line		db	"+-----------------+", 10
string		db	"| exx = .... .... |", 10
lineLen 	equ	$-string
reg		equ	string+3
word1		equ	string+8

		section	.text

;;; ---------------------------------------------------------
;;; dumpRegs: dumps the contents of the 6 main registers (eax
;;; ebx, ecx, edx, esi and edi) in a box on the screen.
;;; the screen.  Does not modify any register
;;; ---------------------------------------------------------
dumpRegs:	pushad

;;; put all the registers to print in the stack.  The loop
;;; will pop each one, one at a time, once per loop.
	
		push	edi
		push	esi
		push	edx
		push	ecx
		push	ebx
		push	eax

;;; print top bar
		call	printBar
	
;;; prepare to loop 6 times (6 registers )
		mov	ecx, 6
		mov	esi, 0

.for		pop	ebx			;get value of register to convert from stack
		push	ecx			;save loop counter
		lea	eax, [regs + esi*2]	;get address of string representing register
	
		mov	ax, word [eax] 		;ax gets "ax" or "bx" or "cx" or ... "di"
		mov	word[reg], ax		;modify string with name of register
	
		mov	edx, word1 		;edx points to buffer where to store hex digits
						;ebx contains register to convert
		call 	storeDWord		;store hex equivalent of ebx in string
	
		mov	ecx, string 		;print the whole string
		mov	edx, lineLen
		call	printInt80
		inc	esi			;index into register names incremented
		pop	ecx			;get loop counter back
		loop	.for

;;; print bottom bar
		call 	printBar
	
		popad
		ret

;;; ---------------------------------------------------------
;;; storeDWord: gets
;;; 	ebx: register to convert
;;; 	edx: address where to put information
;;; ---------------------------------------------------------
		
storeDWord:	rol	ebx, 16			;bring most sig word in least sig word
		call	storeWord
	
		inc	edx			;make edx skip space in string
	
		rol	ebx, 16			;get lower byte back in least sig pos
		call	storeWord
		
		ret

;;; ---------------------------------------------------------
;;; storeWord: gets
;;;     bx: word to convert
;;; 	edx: address where to put information. edx incremented by 4
;;; ---------------------------------------------------------
storeWord:	rol	bx, 8			;put most sig byte of bx in lower position
		call	storeByte		;and convert it.  Store it in where edx 
						;points to. 
		rol	bx, 8			;same with lower nybble
		call	storeByte
		ret
	
;;; ---------------------------------------------------------
;;; storeByte: gets
;;;     bl: byte to convert
;;; 	edx: address where to store information.  edx incremented by 2 automatically
;;; ---------------------------------------------------------
storeByte:	push	ebx
		push	eax
	
		rol	bl, 4			;get upper nybble in lower position (LSB)
		mov	al, bl			;play with al now
		and	eax, 0x0000000F		;clear all but the least significant nybble
		add	eax, hex		;get ascii in hex array equivalentn to nybble
		mov	al, [eax] 		;hex digit now in bl
		mov	byte [edx], al		;store ascii in string
		inc	edx

		rol	bl, 4			;get lower nybble back
		mov	al, bl			;play with al
		and	eax, 0x0000000F
		add	eax, hex
		mov	al, [eax]
		mov	byte [edx], al
		inc	edx
	
		pop	eax
		pop	ebx
		ret
		
;;; ---------------------------------------------------------
;;; printInt80: prints on the screen the string whose address
;;; is in ecx and length in edx.
;;; does not modify registers
;;; ---------------------------------------------------------
printInt80:	push	eax
		push	ebx
	
		mov	eax, 4
		mov	ebx, 1
		int	0x80
	
		pop	ebx
		pop	eax
		ret
	
;;; ---------------------------------------------------------
;;; printBar: prints the horizontal bar
;;; does not modify registers
;;; ---------------------------------------------------------
printBar:	push	ecx
		push	edx
	
		mov	ecx, line
		mov	edx, lineLen
		call	printInt80
	
		pop	edx
		pop	ecx
		ret

Problem #2

;;; ; hw8b.asm
;;; ; Gavi Levy Haskell
;;; ; 231a-ae
;;; ;
;;; ; Uses functions to print the first ten
;;; ; lines of the Pascal Triangle in hex
;;; ;
;;; ; prints:
;;; ;
;;; ;   01 00 00 00 00 00 00 00 00 00
;;; ;	01 01 00 00 00 00 00 00 00 00
;;; ;	01 02 01 00 00 00 00 00 00 00
;;; ;	01 03 03 01 00 00 00 00 00 00
;;; ;	01 04 06 04 01 00 00 00 00 00
;;; ;	01 05 0A 0A 05 01 00 00 00 00
;;; ;	01 06 0F 14 0F 06 01 00 00 00
;;; ;	01 07 15 23 23 15 07 01 00 00
;;; ;	01 08 1C 38 46 38 1C 08 01 00
;;; ;	01 09 24 54 7E 7E 54 24 09 01	
;;; ;
;;; ;
;;; ;     nasm -f elf -F stabs hw8b.asm
;;; ;     ld -melf_i386 -o hw8b hw8b.o
;;; ;     ./hw8b
	
	;; -----------------
	;; DATA SECTION
	;; -----------------
	section	.data
Pascal	times 10 db 0
hexChr	db	"0123456789ABCDEF"
return	db	10
space	db	" "
	
	;; -----------------
	;; CODE SECTION
	;; -----------------
	section	.text
	global	_start
_start:
	mov	ebx, Pascal	; pass address of array in ebx
	call	init		; store 0 in Pascal array and 1
				; in first cell
	mov	ecx, 10		
for:	mov	ebx, Pascal	; pass address of array
	call	printArray	; print Pascal array

	mov	ebx, Pascal
	call 	nextLine	; compute next line of triangle

 	loop	for

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

;;; init
;;; recieves address of Pascal in ebx
;;; modifies no registers
init:
	mov	dword[ebx], 0	; change first 4 terms to zero
	mov	dword[ebx + 4], 0 ; change next 4 terms to 0
	mov	word[ebx + 8], 0  ; change last 2 terms to 0
	mov	byte[ebx], 1	; change first term of array to 1
	ret

;;; printArray
;;; recieves address of Pascal in ebx
;;; modifies eax, ebx, edx
printArray:
	push	ecx		; save outer loop position
	mov	ecx, 10
.for:
	push	ecx		; save loop position
	push	ebx		; save address

 	mov	cl, byte[ebx] 	; first digit
	ror	ecx, 4	      	; get correct digit
 	and	ecx, 0x0F	; keep only this digit
 	add	ecx, hexChr	; add address of hexChr
 	mov	eax, 4
 	mov	ebx, 1
 	mov	edx, 1
 	int	0x80		; print first digit

	pop	ebx
	push	ebx
 	mov	cl, byte[ebx] 	; second digit
 	and	ecx, 0x0F	; keep only this digit
 	add	ecx, hexChr	; add address of hexChr
 	mov	eax, 4
 	mov	ebx, 1
 	mov	edx, 1
 	int	0x80		; print second digit

	mov	eax, 4
	mov	ebx, 1
	mov	ecx, space
	mov	edx, 1
	int	0x80		; print space
	
	pop	ebx
	pop	ecx		; retrieve loop position
	add	ebx, 1
	
	loop	.for		; retrieve outer loop position

	mov	eax, 4
	mov	ebx, 1
	mov	ecx, return	; return
	mov	edx, 1
	int	0x80		; next line
	
	pop	ecx
	ret

;;; nextLine
;;; recieves address of Pascal in ebx
;;; modifies eax, ebx
nextLine:
	push	ecx		; save outer loop position

	mov	ecx, 9
	add	ebx, 9
.for:
	push	ecx		; save loop position
	mov	al, byte[ebx - 1] ; n = row[x - 1]
	add	byte[ebx], al	; row[x] += n
	dec	ebx		; x -= 1
	pop	ecx		; retrieve loop position
	loop	.for

	pop	ecx		; retrieve loop position
	ret