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!

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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

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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

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How big is a 32-bit int?

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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

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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

REVIEW

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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

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Exercise

alpha db 3beta dw 4x dd 6

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

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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

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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

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

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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

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

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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

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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

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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

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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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