CSC231 - Assembly€¦ · inc reg32 inc mem8 inc mem16 inc mem32 alpha db 3 beta dw 4 x dd 0 inc al...

mith College

Computer Science

Dominique Thiébaut dthiebaut@smith.edu

CSC231 - AssemblyWeek #6 Fall 2019

D. Thiebaut, Computer Science, Smith College

Outline

• More arithmetic instructions

• MUL is special…

• DIV is too!

• Mixing data types

• Logical Instructions (AND, OR, NOT, XOR)

• Negative Numbers (next week?)

D. Thiebaut, Computer Science, Smith College

More ArithmeticInstructions

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ALUALU

D. Thiebaut, Computer Science, Smith College

ALUALU

Right now, we are dealing only

with UNSIGNED integers!

D. Thiebaut, Computer Science, Smith College

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

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decdec reg8dec reg16dec reg32dec mem8dec mem16dec mem32

alpha db 3beta dw 4x dd 6

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

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

dec operand

D. Thiebaut, Computer Science, Smith College

mulmul reg8mul reg16mul reg32mul mem8mul mem16mul mem32

mul operand

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Observation

1001x 1110

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mulmul reg8mul reg16mul reg32mul mem8mul mem16mul mem32

alpha db 3beta dw 4x dd 6

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

D. Thiebaut, Computer Science, Smith College

This has tremendously important consequences!

D. Thiebaut, Computer Science, Smith College

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(); }}

D. Thiebaut, Computer Science, Smith College

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

D. Thiebaut, Computer Science, Smith College

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

D. Thiebaut, Computer Science, Smith College

Java's Attitude

Pentium

int x, y, z; x = … y = … z = x * y;

ALUmul

x

y

z

RAM

D. Thiebaut, Computer Science, Smith College

Java's Attitude

Pentium

int x, y, z; x = … y = … z = x * y;

ALUmul

x

y

z

RAM

eax

eaxedx

D. Thiebaut, Computer Science, Smith College

Java's Attitude

Pentium

int x, y, z; x = … y = … z = x * y;

ALUmul

x

y

z

RAM

eax

eaxedx

D. Thiebaut, Computer Science, Smith College

Java's Attitude

Pentium

int x, y, z; x = … y = … z = x * y;

ALUmul

x

y

z

RAM

eax

eaxedx

D. Thiebaut, Computer Science, Smith College

Same Computation in Python…

D. Thiebaut, Computer Science, Smith College

Same Computation in Python…

Interpreted

vs. Compiled

Languages

D. Thiebaut, Computer Science, Smith College

How big is a 32-bit int?

D. Thiebaut, Computer Science, Smith College

Ranges (Unsigned Integers)

8 bits 0 - 255 16 bits 0 - 65,535 32 bits 0 - 4,294,967,295

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Puzzling Behavior

int x = 1;

for (int i=0; i<40; i++ ) { System.out.println( x ); x = x * 2;}

What is the output?

getcopy JavaMulBy2.java

D. Thiebaut, Computer Science, Smith College

mulmul reg8mul reg16mul reg32mul mem8mul mem16mul mem32

alpha db 3beta dw 4x dd 6

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

REVIEW

D. Thiebaut, Computer Science, Smith College

divdiv reg8div reg16div reg32div mem8div mem16div mem32

alpha db 3beta dw 4x dd 6;compute beta/alpha mov ax, word[beta] div byte[alpha];quotient in al;remainder in ah

div operand R : Q edx:eax <— edx:eax / operand32 dx:ax <— dx:ax / operand16 ah:al <— ax / operand8

D. Thiebaut, Computer Science, Smith College

Exercise

alpha db 3beta dw 4x dd 6

Compute x = 2*alpha +3*beta + x - 1

D. Thiebaut, Computer Science, Smith College

D. Thiebaut, Computer Science, Smith College

Logical Instructions

AND, OR, NOT, XOR

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Is (x,y) inside Rectangle?

x1,y1

x2,y2

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a b a and bF F FF T FT F FT T T

Truth Table

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a b a and bF F FF T FT F FT T T

a b a and b0 0 00 1 01 0 01 1 1

D. Thiebaut, Computer Science, Smith College

a b a and bF F FF T FT F FT T T

a b a and b0 0 00 1 01 0 01 1 1

a b a or b0 0 00 1 11 0 11 1 1

D. Thiebaut, Computer Science, Smith College

a b a and bF F FF T FT F FT T T

a b a and b0 0 00 1 01 0 01 1 1

a b a or b0 0 00 1 11 0 11 1 1

a b a xor b0 0 00 1 11 0 11 1 0

D. Thiebaut, Computer Science, Smith College

a b a and bF F FF T FT F FT T T

a b a and b0 0 00 1 01 0 01 1 1

a b a or b0 0 00 1 11 0 11 1 1

a b a xor b0 0 00 1 11 0 11 1 0

a not a

0 1

1 0

D. Thiebaut, Computer Science, Smith College

10010and 11100

10010 or 11100

10010xor 11100

not 11100

D. Thiebaut, Computer Science, Smith College

Instruction Feature

AND Good for setting bits to 0

OR Good for setting bits to 1

XOR Good for flipping bits

NOT Good for complementing all the bits

Image from http://www.staugustinechico.com/wp-content/uploads/2015/05/remember.jpg

D. Thiebaut, Computer Science, Smith College

10010and 11100

10010 or 11100

10010xor 11100

not 11100

10000 11110 01110

00011

Instruction Feature

AND Good for setting bits to 0

OR Good for setting bits to 1

XOR Good for flipping bits

NOT Good for complementing all the bits

D. Thiebaut, Computer Science, Smith College

andand op8,op8and op16,op16and op32,op32 op: mem, reg, imm

alpha db 0xf3beta dw 4x dd 6

and byte[alpha],7 mov ax,0x1234 and ax,0xFF00

and dword[x], 2

and dest, src

D. Thiebaut, Computer Science, Smith College

oror op8,op8or op16,op16or op32,op32 op: mem, reg, imm

alpha db 3beta dw 4x dw 0x0F06

or byte[alpha],4 mov ax,0x1234 or ax,0xFF00

or word[x], 15

or dest, src

D. Thiebaut, Computer Science, Smith College

xorxor op8,op8xor op16,op16xor op32,op32 op: mem, reg, imm

alpha db 3beta dw 4x dd 0xF06

xor byte[alpha],0x0F mov ax,0x1234 xor ax,0xFF00

xor dword[x], 15

xor dest, src

D. Thiebaut, Computer Science, Smith College

notnot op8 not op16 not op32 op: mem, reg

alpha db 3beta dw 4x dd 0xF06

not byte[alpha] mov ax,0x1234 not ax

not dword[x]

not oprnd

D. Thiebaut, Computer Science, Smith College

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