Microsoft 10 Basic_Arithmetic_Instructionsx Basic Arithmetic Instructions

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Lecture 10:

Lecture

10:

Basic Arithmetic Instructions

Today’s Goals

R i Additi d S bt ti

•

R

ev

i

ew

Additi

on an

d

S

u

bt

rac

ti

on

•Use Multiple Precision arithmetic to add and subtract large

b

num

b

ers.

•Practice writing assembly programs.

Addition and Subtraction

•

8 bit addition

From Lecture 8

We will use ADCA(B) and

SBCA

(

B

)

to do multi-

•

8

bit

addition

ABA: (A) + (B) A; Note that there is no AAB instruction!

ADDA: (A) + (M) A

•ADDA $1000

ADDB (B) (M)



B

()

precision addition or

subtraction



ADDB

:

(B)

+

(M)



B

•ADDB #10

ADCA: (A) + (M) + C A

ADCB: (B) + (M) + C B

•8 bit subtraction

SBA: (A) – (B) A; Subtract B from A (Note: not SAB instruction!)



SUBA: (A)

–

(M)



A; Subtract M from A

SUBA:

(A)

(M)



A;

Subtract

M

from

A

SUBB: (B) – (M) B

SBCA: (A) – (M) – C A

SBCB: (B) – (M) – C BThere is a pattern that make you

be easy to remember the

•16 bit addition and subtraction

ADDD: (A:B) + (M:M+1) A:B

SUBD: (A:B) – (M:M+1) A:B

ABX (B) (X)



X

be

easy

to

remember

the

instructions!!!

1. The last letter in these

instructions is the destination!



ABX

:

(B)

+

(X)



X

ABY: (B) + (Y) Y2. Also it comes to the first in the

operation

Precision?

Th t

ii

ift dt ft

th i f it

•

Th

e

t

erm prec

i

s

i

on

i

s o

ft

en use

d

t

o re

f

er

t

o

th

e s

i

ze o

f

a un

it

of data manipulated by the processor.

Si l

ii

f t i t ti th t i l t

•

Si

ng

l

e-prec

i

s

i

on re

f

ers

t

o

i

ns

t

ruc

ti

ons

th

a

t

man

i

pu

l

a

t

e one

byte at a time.

ADDA, ADDB, ABA, SUBA, SUBB, SBA

•Double-precision refers to two-byte operation.

ADDD

,

SUBD

,

ABX: (B) + (X) X, ABY: (B) + (Y) Y

•Multi-

p

recision

p

Adding and subtracting numbers longer than single precision

introduce an issue.



Carries

and

borrows

need to

propagate

through a number



Carries

and

borrows

need

to

propagate

through

a

number

.

Example

Mlti

i i dditi i f d b t t ti

Adding two quadruple-precision numbers

•

M

u

lti

-prec

i

s

i

on a

dditi

on

i

s per

f

orme

d

one

b

y

t

e a

t

a

ti

me,

beginning with the least significant byte.

•92FF45B716 ORG $1200

•6D325D8816 num1

D

C.B

$

92, $FF, $45, $B7

num2 DC.B $6D, $32, $5D, $88

ans DS.B 4

1

1

1

O

RG

$

2000

LDAA num1+3 ; 1

ADDA num2+3 ; 2

STAA ans+3 ; 3

92 FF 45 B7

L

DAA

n

um1+2

;

4

ADCA num2+2 ; 5

STAA ans+2 ; 6

LDAA num1+1 ; 7

6D 32 5D 88

+

-----------

ADCA

n

um2+1

;

8

STAA ans+1 ; 9

LDAA num1 ; 10

ADCA num2 ; 11

+

-----------

3

F

A

3

3

100

S

TAA

a

ns

;

12

SWI ; 13

Program Trace

Trace Line PC A N Z V C

1 1 2003

2 2 2006

3

3

2009

B7100-

3F0011

3F

0

0

0

1

ORG $1200

num1 DC.B $92,$FF,$45,$B7

num2 DC.B $6D,$32,$5D,$88

ans DS.B 4

3

3

2009

4 4 200C

5 5 200F

3F

0

0

0

1

450001

A

3

1

0

1

0

ORG $2000

LDAA num1+3 ; 1

ADDA num2+3 ; 2

6 6 2012

7 7 2015

3

0

0

A31000

FF1000

STAA ans+3 ; 3

LDAA num1+2 ; 4

ADCA num2+2 ; 5

STAA ans+2 ; 6

8 8 2018

9 9 201B

10

10

201E

310000

310001

92

1

0

0

1

LDAA num1+1 ; 7

ADCA num2+1 ; 8

STAA ans+1 ; 9

LDAA num1 ; 10

10

10

201E

11 11 2021

12 12 2022

92

1

0

0

1

000101

000101

ADCA num2 ; 11

STAA ans ; 12

SWI ; 13

13 13 2024 -----

Another Example

Cl lt

t

bt

ff

bt

id

•

C

a

l

cu

l

a

t

e a

t

wo-

b

y

t

esum o

f

an array o

f

one-

b

y

t

e uns

i

gne

d

numbers.

Ri t

•

R

equ

i

remen

t

s

Variable

ovflow

should be $00 if the sum is valid. Otherwise, $ff.

The address of the arra

y

of one-b

y

te unsi

g

ned inte

g

ers is

y

yg g

supplied at $1030.

The length of the array is a one-byte value supplied in $1032.



Ovflow

must be assigned to address

$1040

Ovflow

must

be

assigned

to

address

$1040

.

The sum is returned in locations $1041 and $1042.

Flowchart

SEQ

Start 1:clearsumand

overflow

2:pointtothe

startofthearray

WDO

3:getcopyof

arraylength

4:Thereareno

moreelement

s

9:End

SEQ

true

false

WDO

6

fl

ITE

SEQ

true

5:sum<=

sum+element

7:indicate

6

:noover

fl

ow

occurs

true

false

overflow

8:preparefor

nextloop

;----------------------------------------------------------------------

; variable/data section

o

rg $1030

array ds.w 1 ; address of the array

length ds.b 1 ; length of the array

org $1040

fl

db

1

fl fl $00 lid $ff i lid

ov

fl

ow

d

s.

b

1

; over

fl

ow

fl

ag.

$00

= va

lid

,

$ff

=

i

nva

lid

sum ds.w 1 ; 2-byte sim of unsigned numbers in the array

;----------------------------------------------------------------------

; code section

;

code

section

org $2000

movw #0,sum ; 1. clear sum

movb #0,ovflow ; clear ovflow

l

dd #0

;

clear A and B

ldx array ; 2. point to the start of the array

ldab length

tfr D,Y ; 3. get copy of array length

loop beq done ; 4. no more elements?

l

cl

ra

ldab 0,X ; load an element to B

addd sum ; 5. sum = sum + element

std sum ; store D to sum

bcc

sum ok

; 6 no overflow?

bcc

sum_ok

;

6

.

no

overflow?

movb #$ff,ovflow ; 7. indicate overflow

sum_ok inx ; 8. prepare for next loop

dey ; "

b

ra loop

;

g

o to "loop"

done swi

Changes for Two-Byte Length

H lik l i i d fl i th i i l ?

•

H

ow

lik

e

l

y

i

s uns

i

gne

d

over

fl

ow

i

n

th

e or

i

g

i

na

l

program

?

Cannot happen. The largest possible sum is $FE01 ($FF * $FF).

Wh difi i d d h dl

bl h?

•

Wh

at mo

difi

cat

i

ons are nee

d

e

d

to

h

an

dl

e two-

b

yte

l

engt

h?

Replace DS.B 1 with DS.W 1

Re

p

lace LDAB

,

TFR with LDY

p

,

;----------------------------------------------------------------------

; variable/data section

o

rg $1030

array ds.w 1 ; address of the array

lengthlength ds.wds.w 11; length of the array

org $1040

fl

db

1

fl fl $00 lid $ff i lid

ov

fl

ow

d

s.

b

1

; over

fl

ow

fl

ag.

$00

= va

lid

,

$ff

=

i

nva

lid

sum ds.w 1 ; 2-byte sim of unsigned numbers in the array

;----------------------------------------------------------------------

; code section

;

code

section

org $2000

movw #0,sum ; 1. clear sum

movb #0,ovflow ; clear ovflow

l

dd #0

;

clear A and B

ldx array ; 2. point to the start of the array

; ldab length

; tfr D,Y ; 3. get copy of array length

ldyldy lengthlength ; 3. get copy of array length

l

b

d

4l?

l

oop

b

eq

d

one

;

4

. no more e

l

ements

?

clra

ldab 0,X ; load an element to B

addd sum ; 5. sum = sum + element

std

sum

;

store D to sum

std

sum

;

store

D

to

sum

bcc sum_ok ; 6. no overflow?

movb #$ff,ovflow ; 7. indicate overflow

sum_ok inx ; 8. prepare for next loop

d

ey

;

"

bra loop ; go to "loop"

done swi

Changes for Signed Numbers

;

----------------------------------------------------------------------

;

; program

org $2000

movw #0,sum ; 1. clear sum

movb #0,ovflow ; clear ovflow

l

dd #0

;

clear A and B

ldx array ; 2. point to the start of the array

ldab length

tfr D,Y ; 3. get copy of array length

loop

beq

done

;

4 no more elements?

loop

beq

done

;

4

.

no

more

elements?

clra

ldab 0,X ; load an element to B

bplbpl skipskip ; check if B is positive

ldaaldaa

#$ff#$ff

;

extend the sign bit if B is negative

ldaaldaa

#$ff#$ff

;

extend

the

sign

bit

if

B

is

negative

skipskip

addd sum ; 5. sum = sum + element

bvcbvc sum_ok ; 6. no overflow?

movb #$ff,ovflow ; 7. indicate overflow

sum

_

ok

; std clears the v bit so std is moved to here

stdstd sumsum ; store D to sum

inx ; 8. prepare for next loop

dey

"

dey

;

"

bra loop ; go to "loop"

done swi

Questions?

Wrap-up

Mltil

ii

ith ti t dd d bt t l

What we’ve learned

•

M

u

lti

p

l

e-prec

i

s

i

on ar

ith

me

ti

c

t

o a

dd

an

d

su

bt

rac

t

l

arge

numbers.

Mti

iti i bl

•

M

ore prac

ti

ce wr

iti

ng programs

i

n assem

bl

y

What to Come

Ad d ith ti i t ti

•

Ad

vance

d

ar

ith

me

ti

c

i

ns

t

ruc

ti

ons

•Boolean logic instructions