Neon Floating Point Example

00:01

Hello. This is Dr Miller, and this is Episode 12.4 of Assembly.

00:06

Today, we're going to give a floating point Example.

00:10

So what's our problem? To be solved. So we're going to read it radius from the user, and then we'll go ahead and calculate and print the area. And what we'll do is we'll end up using neon instructions for that.

00:20

So I already got the project set up.

00:24

So we're gonna have a couple of messages here,

00:30

so it'll ask them entered, uh,

00:33

radius.

00:46

We will have to scan the number from the user, so used percent f

00:55

and I will print off our result

00:58

area.

01:04

I will put a new line in here, so it's nice for the user. So up here, we won't put a new line because usual type something and then the light enter. So we might as well make it look nice.

01:15

And they will declare a variable. So we'll declare pie

01:21

and I dont be three.

01:26

That will be

01:29

3.1 for

01:32

15

01:34

nine to

01:37

65

01:41

359 So I'm gonna use a double here, so we get a little bit more accuracy.

01:49

So let's set up our stack. So we got our frame pointer and our link register.

01:55

We'll go ahead and set up the stack.

02:08

Well, sidetrack some for here. Just pick a number.

02:13

Um, when we go to restore, we're going to do so. But SPF p

02:19

the number four because we added So we do a subject.

02:23

So now we'll go ahead and print off our result. LD R zero

02:29

Get our first format

02:35

read in cold print off and here less declare our

02:38

functions that we're going to use

02:45

current events can up. So we printed off our question for the user and then we're going to

02:50

go ahead and load it. So sub

02:53

are one is where we're going to use it.

02:55

It's gonna be our pointer saw frame pointer

02:59

and then minus eight. So the number eight

03:04

So that's where the data is located.

03:06

We'll do. LD R R zero

03:09

format A. Which is our scan f will go ahead and call branch of links can if

03:16

and then So now we've got our result in there. And so what we want to do is we want to copy it out. So vector L d r.

03:25

We'll just pick a register. So I'm gonna pick s 15

03:30

and we're going to get the value at the frame pointer

03:34

minus the number eight. And the way arm does it, you have to put the hashtag care to tell that it's a number.

03:42

So we're going to frame Pointer minus eight,

03:44

and then we'll use V convert

03:47

into a floating 0.64

03:52

from a floating 0.32

03:55

into D seven

03:58

and we're going to use s 15

04:06

all right?

04:10

And then what we want to do is we're gonna have to do our multiplication. So that's going to give us our Radius, which is in d seven

04:17

and go ahead and square that so we can save the mall

04:21

a 64 bit

04:25

floating point.

04:27

You mean to say d seven is d seven times d seven. It's That's an easy way to square something,

04:33

and then we're gonna want to go ahead and load our value for pi in so LD r r. Zero The address of pie

04:42

Well, the R D r two

04:46

value at our zero. So again,

04:50

R two and r three are gonna be loaded

04:57

just so we don't forget that and then

05:00

we can convert that into a 64 bit. So again, USVI move

05:09

because they're in our to win our three floating 30.64

05:14

into will use d eight

05:16

and we're gonna load R two and r three Little copy those into that register

05:25

we can now multiply

05:27

are things together. So we got d eight has pie and d seven has the value squared.

05:32

So instead of the more

05:36

we're gonna do floating 0.64

05:40

Okay,

05:41

g seven, his arrest or it and we're gonna multiple i d seven times d eight.

05:47

So now they're multiplied in stored in D seven.

05:51

So again we can use v move. And so one of the things to understand is that

05:57

when print off is gonna print it, it's gonna actually just use r two and R three, and we won't use our one because our first value is a

06:03

ah double, and so it's not going to use it. So when we do RV move, we're going to move our two into r two and R three.

06:14

The value that's in d seven, slot a copy it to those two registers. We're not going to set our zero, but we will say are one.

06:21

Sorry, we're not going to set our one, but we will set our zero.

06:26

The load register are zero. We'll get our format that we want a print, so it's four minute

06:31

be

06:33

and then we'll go ahead and

06:35

called friend F

06:38

So branch of link

06:40

and then we're at the bottom of our function. So let's try this

06:47

and looks like I

06:49

had a typo which nobody could tell me about. So

06:55

I miss types can f

06:59

There we go

07:08

when I think I missed type format here.

07:15

All right,

07:16

So far Radius is 10 10 times 10 is 100

07:20

100 times pi is 314.

07:28

All right, so we gave an example using floating point. So we did some loading of registers. We did some reading from scan half and we also did some printing with Brent F.

07:39

So in the future will talk about us and I m d and then thumb mode and conditional execution.