csc231 - assembly · 2019. 10. 9. · d. thiebaut, computer science, smith college a dd 3 b dd 5...

mith College

Computer Science

Dominique Thiébaut [email protected]

CSC231 - AssemblyWeek #5 Fall 2019

D. Thiebaut, Computer Science, Smith College

Outline

• Working with Byte, Word and DWord Variables

• Step-by-Step Execution of a Program

• Speed of N-Queens

• Review of binary/hexadecimal/decimal


Misc. Notes & Review


Note: You Can AddA Register to Itself

; x = 2 * (a-b)

mov eax, dword[a] ; eax <- asub eax, dword[b] ; eax <- a-badd eax, eax ; eax <- eax+eax ; eax <- 2*(a-b)mov dword[x], eax ; x <- 2*(a-b)


The Pentium DataRegisters

eax

ebx

ecx

edx

ax

bx

cx

dx

ah al

bh bl

ch cl

dh dl


Review: Our Goal was…

int x, y, sum;

x = 3;y = 5;sum = x + y;


Same with Short Ints

short x, y, sum;

x = 3;y = 5;sum = x + y;

Translate this into Assembly


Same with Bytes

byte x, y, sum;

x = 3;y = 5;sum = x + y;



With an Array!

int A[3];

A[0] = 3;A[1] = 5;A[2] = A[0]+A[1]



Exerciseextern _printIntextern _println

section .dataa dw 1b dw 2c dw 3sum dw 0msg db "hello!",10

section .textglobal _start

_start:mov eax, dword[a]add eax, dword[b]add eax, dword[c]mov dword[sum],eaxcall _printIntcall _println

mov ecx, msgmov edx, 7mov eax, 4mov ebx, 1int 0x80

What is the output

of this program?


Exercisecs231a@marax:~ $ nasm -f elf week5exercise.asm cs231a@marax:~ $ ld -melf_i386 week5exercise.o 231Lib.o -o week5exercise cs231a@marax:~ $ ./week5exercise 327686 llo!

why?


Exercisesection .data

a db b db c dw d dw e dd f db

section .text

reconstruct the declarations of a, b, c, d, e

and f.

99

88

77

66

55

44

33

22

1f

1a

11

00

a

typical

midterm

question!

hex


Follow a stepby step execution

of the program


8 9 section .data 10 00000000 03000000 a dd 3 11 00000004 05000000 b dd 5 12 00000008 00000000 sum dd 0 13 14 ;;; 15 ;;; code area 16 ;;; 17 18 section .text 19 global _start

20 00000000 A1[00000000] _start: mov eax, dword[a] ;eax <-- a 21 00000005 0305[04000000] add eax, dword[b] ;eax <-- eax+b = a+b 22 0000000B 83E801 sub eax, 1 ;eax <-- eax-1 = a+b-1 23 0000000E A3[08000000] mov dword[sum], eax ;sum <-- eax = a+b-1

24 ;;; exit() 25 00000013 B801000000 mov eax,1 26 00000018 BB00000000 mov ebx,0 27 0000001D CD80 int 0x80 ; final system call


a dd 3b dd 5sum dd 0

100 mov eax, dword[a]105 add eax, dword[b]10A sub eax, 110E mov dword[sum], eax

eax

ebx

ecx

edx

eip




eax

ebx

ecx

edx

eip



eax

ebx

ecx

edx

eip

Tick!




eax

ebx

ecx

edx

eip



eax

ebx

ecx

edx

eip



eax

ebx

ecx

edx

eip

Tick!




eax

ebx

ecx

edx

eip



eax

ebx

ecx

edx

eip



eax

ebx

ecx

edx

eip



eax

ebx

ecx

edx

eip

Tick!


Frequency: 3.2 GHz

cycle: 1/3.2 GHz =0.3125 ns

sec ms us ns


Arduino

;hello.asm; turns on an LED which is connected to PB5 (digital out 13)

.include "./m328Pdef.inc"

ldi r16,0b00100000out DDRB,r16out PortB,r16

Start:rjmp Start

Clock speed: 16 MHz

~1/200 speed of Pentium

http://www.science.smith.edu/dftwiki/index.php/Comparing_Different_Computers_with_N_Queens_Program



Raspberry Pi

/* -- first.s *//* This is a comment */.global main /* 'main' is our entry point and must be global */ main: /* This is main */ mov r0, #2 /* Put a 2 inside the register r0 */ bx lr /* Return from main */

Clock speed: 1.4 GHz

~1/3 speed of Pentium




N-Queens Problem





We Stopped Here Last Time…


5:30-6:30 p.m.


Evening Plans?

Let’s go to Boston this evening. I’ll drive!


Evening Plans?

Let’s go to downtown Northampton.


Know what's in your toolbox!


Summit: Fastest SupercomputerOak Ridge National Laboratory

https://www.top500.org/lists/2019/06/




NUMBER SYSTEMSNUMBER SYSTEMS


Decimal

• Number of digits, the base

• Count in decimal

• Express number as sum of products

• Add two digits

• Add two numbers


Binary


• Count in binary


• Add two digits

• Add two numbers


Base 3


• Count in base 3


• Add two digits

• Add two numbers


Hexadecimal


• Count in hex


• Add two digits

• Add two numbers


Super

Useful!

Conversion0000 0 0 0001 1 1 0010 2 2 0011 3 3 0100 4 4 0101 5 5 0110 6 6 0111 7 7 1000 8 8 1001 9 9 1010 A 10 1011 B 11 1100 C 12 1101 D 13 1110 E 14 1111 F 15


Binary to Decimal,Decimal to

Binary ConversionReview

Shifting


101001 =


101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20


101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

= 32 + 0 + 8 + 0 + 0 + 1 = 41d


101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

= 32 + 0 + 8 + 0 + 0 + 1 = 41d

101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

2 2


101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

= 32 + 0 + 8 + 0 + 0 + 1 = 41d

101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

2 2

= 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20 2 2 2 2 2 2


101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

= 32 + 0 + 8 + 0 + 0 + 1 = 41d

101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

2 2

= 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20 2 2 2 2 2 2 = 1x24 + 0x23 + 1x22 + 0x21 + 0x20


101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

= 32 + 0 + 8 + 0 + 0 + 1 = 41d

101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

2 2

= 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20 2 2 2 2 2 2 = 1x24 + 0x23 + 1x22 + 0x21 + 0x20 = 10100


101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

= 32 + 0 + 8 + 0 + 0 + 1 = 41d

101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

2 2

= 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20 2 2 2 2 2 2 = 1x24 + 0x23 + 1x22 + 0x21 + 0x20

= 10100 = 16 + 0 + 4 + 0 + 0 = 20d


Dividing by the baseextracts the leastsignificant digit


Python Program# prompts user for an integer# decomposes the integer into binary

x = int( input( "> " ) )binary = ""

while True: if x==0:

break

remainder = x % 2 quotient = x // 2

if remainder == 0: binary = "0" + binary else: binary = "1" + binary

print( "%5d = %5d * 2 + %d quotient=%5d remainder=%d binary=%16s" % (x, quotient, remainder, quotient, remainder, binary ) )

x = quotient

getcopy decimal2binary.py


Python Program

# prompts user for an integer# decomposes the integer into binary

x = int( input( "> " ) )binary = ""

while True: if x==0:

break

remainder = x % 2 quotient = x // 2

if remainder == 0: binary = "0" + binary else: binary = "1" + binary

print( "%5d = %5d * 2 + %d quotient=%5d remainder=%d binary=%16s" % (x, quotient, remainder, quotient, remainder, binary ) )

x = quotient


Binary to Decimal


101001 = 1x25 + 0x24 + 1x23 + 0x22 + 0x21 + 1x20

= 32 + 0 + 8 + 0 + 0 + 1 = 41d


Binary to Hex


1010010 =


1010010 = 01010010


1010010 = 01010010 = 0101 0010

v


1010010 = 01010010 = 0101 0010

v

0000 0 0001 1 0010 2 0011 3 0100 4 0101 5 0110 6 0111 7 1000 8 1001 9 1010 A 1011 B 1100 C 1101 D 1110 E 1111 F


1010010 = 01010010 = 0101 0010 = 5 2

0000 0 0001 1 0010 2 0011 3 0100 4 0101 5 0110 6 0111 7 1000 8 1001 9 1010 A 1011 B 1100 C 1101 D 1110 E 1111 F


Hex to Binary


5A1F =

0000 0 0001 1 0010 2 0011 3 0100 4 0101 5 0110 6 0111 7 1000 8 1001 9 1010 A 1011 B 1100 C 1101 D 1110 E 1111 F


5A1F = 0101 1010 0001 1111

0000 0 0001 1 0010 2 0011 3 0100 4 0101 5 0110 6 0111 7 1000 8 1001 9 1010 A 1011 B 1100 C 1101 D 1110 E 1111 F


Hex to Decimal


1A2F =


1A2F = 1x163 + Ax162 + 2x161 + Fx160 =


1A2F = 1x163 + Ax162 + 2x161 + Fx160 = 1x4096 + 10x256 + 2x16 + 15x1 =

0000 0 0001 1 0010 2 0011 3 0100 4 0101 5 0110 6 0111 7 1000 8 1001 9 1010 A 1011 B 1100 C 1101 D 1110 E 1111 F


1A2F = 1x163 + Ax162 + 2x161 + Fx160 = 1x4096 + 10x256 + 2x16 + 15x1 = 4096 + 2560 + 32 + 15 =

0000 0 0001 1 0010 2 0011 3 0100 4 0101 5 0110 6 0111 7 1000 8 1001 9 1010 A 1011 B 1100 C 1101 D 1110 E 1111 F


1A2F = 1x163 + Ax162 + 2x161 + Fx160 = 1x4096 + 10x256 + 2x16 + 15x1 = 4096 + 2560 + 32 + 15 = 6703

0000 0 0001 1 0010 2 0011 3 0100 4 0101 5 0110 6 0111 7 1000 8 1001 9 1010 A 1011 B 1100 C 1101 D 1110 E 1111 F


Decimal toHex


Do:Decimal —> Binary

Binary—> Hex


Exercises

http://www.science.smith.edu/dftwiki/index.php/CSC231_Review_of_hexadecimal_number_system




Convert these hexadecimal numbers to binary, and to decimal.

1111

1234

AAAA

F001

FFFF


Convert these decimal numbers to binary, and hexadecimal

65

127


What comes after these hexadecimal numbers, logically?

aaAA

9999

19F

1ABF

FFEF

F00F

ABCDEF


Perform the following additions in hex

1000 + AAAA

1234 + F

1234 + ABCD

FFFF + FFFF


More ArithmeticInstructions


ALUALU

Right now, we are dealing only

with UNSIGNED integers!


incinc reg8inc reg16inc reg32inc mem8inc mem16inc mem32

alpha db 3beta dw 4x dd 0

inc al inc cx inc ebx

inc word[beta] ;beta <- 5 inc dword[x] ;x <- 1

inc operand


decdec reg8dec reg16dec reg32dec mem8dec mem16dec mem32


dec al ;al <- al-1 dec cx dec ebx

dec word[beta] ;beta <- 3 dec dword[x] ;x <- 5

dec operand


mulmul reg8mul reg16mul reg32mul mem8mul mem16mul mem32

mul operand


Observation

1001x 1110


mulmul reg8mul reg16mul reg32mul mem8mul mem16mul mem32


mul byte[alpha] ;ax <- al*alpha mul ebx ;edx:eax <- ; ebx*eax

mul operand edx:eax <— operand32 * eax dx:ax <— operand16 * ax ax <— operand8 * al


This has tremendously important consequences!


public class JavaLimits {

public static void main(String[] args) { // ----------------------------------------------- // a multiplication of ints int x = 0x30000001; int y = 0x30000001;

System.out.println( "x = " + x ); System.out.println( "y = " + y ); int z = x * y;

System.out.println( "z = " + z ); System.out.println(); }}


public class JavaLimits {

public static void main(String[] args) { // ----------------------------------------------- // a multiplication of ints int x = 0x30000001; int y = 0x30000001;

System.out.println( "x = " + x ); System.out.println( "y = " + y ); int z = x * y;

System.out.println( "z = " + z ); System.out.println(); }}

x = 805306369 y = 805306369 z = 1610612737


Same Computation in Python…

csc231 - assembly · 2019. 10. 9. · d. thiebaut, computer science, smith college a dd 3 b dd 5...

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