CSC231 - Assembly · 2019. 10. 9. · D. Thiebaut, Computer Science, Smith College a dd 3 b dd 5...

mith College

Computer Science

Dominique Thiébaut dthiebaut@smith.edu

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

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!

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.

typical

midterm

question!

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

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 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

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

= 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

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

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

= 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

= 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

= 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

= 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:

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:

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

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.

Convert these decimal numbers to binary, and hexadecimal

What comes after these hexadecimal numbers, logically?

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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