CSC231 - Assembly · mith College C omputer Science Dominique Thiébaut dthiebaut@smith.edu CSC231...

mith College

Computer Science

Dominique Thiébaut dthiebaut@smith.edu

CSC231 - AssemblyWeek #8

D. Thiebaut, Computer Science, Smith College

https://xkcd.com/571/

Can't Sleep

Logic Design

Image from http://www.willegal.net/appleii/images/motherboard.jpg

Apple II Motherboard

Nasa Computer(Apollo)

A Bit of History

• Claude Shannon • 21 years old • 1937 • MIT Master's Thesis • All arithmetic operations

on binary numbers can be performed usingboolean logic operators

https://en.wikipedia.org/wiki/Claude_Shannon

https://www.youtube.com/watch?v=xTQDIiSWK_k

Designing a 2-bitAdder with Logic

Processor

carryi

Compute add x, y

x0 y0x1 y1x2 y2xn yn x3 y3

z0z1z2z3zn

+ 0 ____

0+ 1____

1+ 0____

1+ 1____

x0 y0 Carry z0

0 0 0 0

0 1 0 1

1 0 0 1

1 1 1 0

x0 y0 Carry z0

0 0 0 0

0 1 0 1

1 0 0 1

1 1 1 0

Carry = x0 and y0

z0 = x0 xor y0

XORAND

Moral of the Story: Addition is performed

by logic operations using natural binary numbers…

(unsigned arithmetic)

NEGATIVE NUMBERS

How can we represent signed binary numbers when

all we have are bits (0/1)?

Whichever system we use should work

with the binary adder in the ALU…

Binary Hex Unsigned Decimal

0000 0 00001 1 10010 2 20011 3 30100 4 40101 5 50110 6 60111 7 71000 8 81001 9 91010 A 101011 B 111100 C 121101 D 131110 E 141111 F 15

4-bit Nybble

0 000 0 00 001 1 10 010 2 20 011 3 30 100 4 40 101 5 50 110 6 60 111 7 71 000 8 81 001 9 91 010 A 10 1 011 B 111 100 C 121 101 D 131 110 E 141 111 F 15

4-bit NybbleSign Bit

0 000 0 00 001 1 10 010 2 20 011 3 30 100 4 40 101 5 50 110 6 60 111 7 71 000 8 81 001 9 91 010 A 10 1 011 B 111 100 C 121 101 D 131 110 E 141 111 F 15

PositiveNumbers

NegativeNumbers

4-bit Nybble

Signed MagnitudeNumber System

Signed Magnitude Rule: To find the opposite of a number, just flip

its MSB

0 101 (+5)

1 101(-5)

and vice versa…

Signed Magnitude

0 000 0 0 +00 001 1 1 +10 010 2 2 +20 011 3 3 +30 100 4 4 +40 101 5 5 +50 110 6 6 +60 111 7 7 +71 000 8 8 -01 001 9 9 -11 010 A 10 -2 1 011 B 11 -31 100 C 12 -41 101 D 13 -51 110 E 14 -61 111 F 15 -7

4-bit Nybble

Does this System work With the ALU Adder?

Signed Magnitud

e0 000 0 0 +00 001 1 1 +10 010 2 2 +20 011 3 3 +30 100 4 4 +40 101 5 5 +50 110 6 6 +60 111 7 7 +71 000 8 8 -01 001 9 9 -11 010 A 10 -2 1 011 B 11 -31 100 C 12 -41 101 D 13 -51 110 E 14 -61 111 F 15 -7

3 + -3——- = 0

4 + -1——- = 3

1's ComplementNumber System

1's Complement Rule: To find the opposite of a number,

just flip all its bits

0 101 (+5)

1 010(-5)

and vice versa…

1'sComplement

0 000 0 0 +00 001 1 1 +10 010 2 2 +20 011 3 3 +30 100 4 4 +40 101 5 5 +50 110 6 6 +60 111 7 7 +71 000 8 8 -71 001 9 9 -61 010 A 10 -5 1 011 B 11 -41 100 C 12 -31 101 D 13 -21 110 E 14 -11 111 F 15 -0

4-bit Nybble

Does this System work With the ALU Adder?

1'sComplement

0 000 0 0 +00 001 1 1 +10 010 2 2 +20 011 3 3 +30 100 4 4 +40 101 5 5 +50 110 6 6 +60 111 7 7 +71 000 8 8 -71 001 9 9 -61 010 A 10 -5 1 011 B 11 -41 100 C 12 -31 101 D 13 -21 110 E 14 -11 111 F 15 -0

3 + -3——- = 0

4 + -1——- = 3

5 + -3——- = 2

2's ComplementNumber System

2's Complement Rule: To find the opposite of a number,

just flip all its bits, and add 1

0 101(+5)

1 011(-5)

and vice versa…

1 010 + 1

0 100 + 1

2'sComplement

0 000 0 0 +00 001 1 1 +10 010 2 2 +20 011 3 3 +30 100 4 4 +40 101 5 5 +50 110 6 6 +60 111 7 7 +71 000 8 8 -81 001 9 9 -71 010 A 10 -6 1 011 B 11 -51 100 C 12 -41 101 D 13 -31 110 E 14 -21 111 F 15 -1

4-bit Nybble

Does this System workWith the ALU Adder?

2'sComplement

0 000 0 0 +00 001 1 1 +10 010 2 2 +20 011 3 3 +30 100 4 4 +40 101 5 5 +50 110 6 6 +60 111 7 7 +71 000 8 8 -81 001 9 9 -71 010 A 10 -6 1 011 B 11 -51 100 C 12 -41 101 D 13 -31 110 E 14 -31 111 F 15 -1

3 + -3——- = 0

4 + -1 ——- = 3

5 + -3——- = 2

InterestingProperty

• What is the binary representation of -1 as a byte?

• What is the binary representation of -1 as a word?

• What is the binary representation of -1 as a dword?

int x = 0x7fffffff - 5;

for ( int i=0; i<10; i++ )System.out.println( x++ );

getcopy Loop0x7fffffff.java

What did you just learn about Java ints?

negneg op8 neg op16 neg op32 op: mem, reg

alpha db 1beta dw 4x dd 0xF06

neg byte[alpha] mov ax,1234 neg ax

neg dword[x]

neg oprnd

To get the

2's complement

of an int

Range of 2's Comp't. intsBinary Hex Unsigned

Decimal0000 0 00001 1 10010 2 20011 3 30100 4 40101 5 50110 6 60111 7 71000 8 81001 9 91010 A 101011 B 111100 C 121101 D 131110 E 141111 F 15

Type Minimum Maximum # Bytes

unsigned byte 0 255 1

signed byte -128 127 1

unsigned short 0 65,535 2

signed short -32,768 32,767 2

unsigned int 0 4,294,967,295 4

signed int -2,147,483,648 2,147,483,647 4

signed long

−9,223,372,036,854,775,808

9,223,372,036,854,775,807 8

We Stopped Here Last Time

http://www.genengnews.com/media/images/genhighlight/Mar12_2014_8296129_StopSigns_GeronTrialHalt2322361121.jpg

(and finished first exercise on next slide)

The 13th Floorhttps://www.youtube.com/watch?v=dtYdZkPmFoU

The LOOP Instruction

looploop label

x dd 1sum dd 0 mov ecx, 10addUp: mov eax, dword[x] add dword[sum], eax inc dword[x] loop addUp ;ecx<—ecx-1 ;if ecx!=0, ; goto addUp

loop label

looploop label

loop label

looploop label ;ecx <— ecx-1 ;if ecx!= 0, ; goto label ;else continue

loop label

Labels _start: mov eax, 4

mov ecx, 10 for1: … … loop for1 for2: … …

loop for2

• Start with a letter (or a dot)

• End with a colon (when declared)

• Represent an address in the code section

• Must be unique in program

Tracinga Code Example

mov ecx, 3 mov eax, 1for: call _printDec inc eax loop for ;ecx<—ecx-1 ;if ecx!=0, ; goto for

1 2eax

3 2ecx

1 2eax

3 2ecx

1 2 3eax

3 2ecx

1 2 3eax

3 2 1ecx

1 2 3eax

3 2 1ecx

1 2 3 4eax

3 2 1ecx

1 2 3 4eax

3 2 1 0ecx

mov ecx, 3 mov eax, 1for: call _printDec inc eax loop for ;ecx<—ecx-1 ???? ;if ecx!=0, ; goto for

1 2 3 4eax

3 2 1 0ecx

Example 1Sum of 1..10

; computes sum(1,2, …10)x dd 1sum dd 0 mov ecx, 10 mov eax, dword[x]addUP: add dword[sum], eax inc eax loop addUp ;ecx<—ecx-1 ;if ecx!=0, ; goto addUp mov eax, dword[sum] call _printDec

; computes sum(1,2, …10)x dd 1sum dd 0 mov ecx, 10 addUP: add dword[sum], ecx loop addUp ;ecx<—ecx-1 ;if ecx!=0, ; goto addUp mov eax, dword[sum] call _printDec

Do we needeax?

Example 2Fibonaccis

http://i.dailymail.co.uk/i/pix/2016/07/17/13/1A32203E000005DC-3694326-image-m-17_1468760305397.jpg

_start: mov eax, 1 ; fibn mov ebx, 1 ; fibn-1 call _printDec call _println

mov ecx, 10-1 ; we printed 1, 9 more to go for: mov edx, ebx mov ebx, eax add eax, edx call _printDec call _println loop for

getcopy fib.asm

; print the first 10 Fibonacci terms

Looping Through

Arrays

Looping Through

Arrays

LOOP INSTRUCTION

INDIRECTADDRESSINGMODE

Indirect AddressingMode

The addressing mode refers to the way the operand of an instruction is generated. We already know register mode, immediate mode, and direct mode.

Tracing One Example

of Indirect Addressing (Base Addressing)

Memory

0x110450x110460x110470x110480x110490x1104A0x1104B0x1104C

???ebx?al

section .data A db 1,3,0xF0,0x3E,0x56 B db 0x78,0x33,0x12

section .text

_start: mov al, 'z' mov ebx, A mov byte[ebx], 0

mov ebx, B mov byte[ebx], al

Memory

0x110450x110460x110470x110480x110490x1104A0x1104B0x1104C

section .text

???ebx'z'al

Memory

0x110450x110460x110470x110480x110490x1104A0x1104B0x1104C

section .text

11045ebx'z'al

Memory

0x110450x110460x110470x110480x110490x1104A0x1104B0x1104C

section .text

11045ebx'z'al

Memory

0x110450x110460x110470x110480x110490x1104A0x1104B0x1104C

section .text

1104Aebx'z'al

78 'z'

Memory

0x110450x110460x110470x110480x110490x1104A0x1104B0x1104C

section .text

1104Aebx'z'al

Example 2:Setting an Array

to All 0s

; Array Table contains 10 wordsTable dw 1,2,3,4,5,6 dw 7,8,9,10 mov ecx, ____ ;# of elements mov ebx, ____ ;address of ;Tableclear: mov word[ebx], ____;value to store add ebx,____ ;make ebx point ;to next word loop clear ;ecx<—ecx-1 ;if ecx!=0, ; goto clear

ExercisesProblem #1: Store the first 10 Fibonacci terms in an array of ints (32 bits)

Problem #2: Given a DNA sequence of 1,000,000 characters stored in an array of bytes, and all characters in uppercase, transform it into its lowercase equivalent. The characters are A, C, G, T and N.

We stopped here last time…

CSC231 - Assembly · mith College C omputer Science Dominique Thiébaut dthiebaut@smith.edu CSC231...

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