IT Block Example

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Hello. This is Dr Miller, and this is upside 12.13 of assembly

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today. We're going to give a thumb conditional execution example using I t blocks.

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So our thumb conditional execution example. So what we're gonna do is we're going to create a min slash max function using I t blocks.

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So first will define a couple of different messages here.

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So we got a

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which is gonna ask us to enter our numbers,

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and then we're gonna have be

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the max is,

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and we'll put a percent d there

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on a new line.

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All right, so the first thing we need to do is print our first prompt someone load register. Are zero

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the address of a

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branch with link

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to print, two f

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and then we're gonna do branch with Link read,

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and

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that'll have our result in R zero. And then we're gonna go ahead and

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move. Are seven

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copy R, zero intar seven.

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We'll go ahead and copy two lines.

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Read it again and copy it into our eight,

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and then copy it into our nine. So we got our numbers are in our seven r eight and are 93 bread from the user.

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So we're gonna be writing a thumb function. So they've branch with Link Exchange, max.

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And then when we're all done, we'll go ahead and print off our number. So we're gonna do move into our one

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are zero, which is our result.

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Um, load register are zero. We're going to copy into it the value of B,

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and then I wouldn't call Brent death.

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All right, so now our function again, this is gonna be a thumb function.

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Um, So I think here, I need a dot and funk here.

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So dot

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a line

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two tells us this is gonna line on to buy boundaries and then dot from

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function.

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All right, so this is going to be

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our max function,

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So I hadn't push our link register

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at the end. Will do pop of our program counter.

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Okay, so we'll do a compare of r seven and r eight. So these are two of our numbers,

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and then we'll do an if then

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else

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greater than

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because we're trying to find Max,

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so I'll do a move. Right? So it's greater than so I could do a move greater than

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are zero r seven. So seven is bigger. So I'll go ahead and do that. And then we go

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move

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less than or equal to. So anything else are zero or seven.

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Sorry. Are eight.

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All right. So now we know are zero has the bigger of r seven and R eight, and then we can do a compare of r zero

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and our nine,

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and then we'll just do an if then

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less than or equal to, you know, move. Ellie,

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are zero R nine?

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No, but our nine is bigger.

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Our eight is bigger.

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Our seven is bigger. And so we got our three cases for that.

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And you can see in here we don't have any branches. And so our execution just is going to go ahead and just run right through.

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In addition to doing our if them blocks, we also have gotta tell it that we're going to use unified syntax.

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This will allow us to use our if them blocks inside of there.

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All right,

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so we got enter three numbers, one Teoh, three

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or 3 to 1.

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Or one

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33 to,

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you know, go through and work.

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So then we can easily add a minimum function. So here I'm going to,

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um change Be to say,

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Oh,

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the

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men is

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Instead of calling Max, I'll go ahead and call men

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and then I'm gonna copy everything from here down

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so we can dio Yangpu

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Yank, Or why 200 yank and it'll copy all of our lines, and then I can go ahead and put those in

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so we're gonna call the men function,

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and so we basically just need to

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invert all of our conditions here. So instead of saying

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if then else greater than we can go ahead and say

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if then else less than

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change this to less than and this to greater than or equal to

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And then here instead of Ellie Weaken say g t

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she you

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gt

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So now we have changed our

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max function into a min function.

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I guess I can change these here.

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Okay,

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so now when I run at an or three numbers one to you, three

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to the 21

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312 it gives us the right number.

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So today we created Botham in and a max function

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using conditional execution, and we use I t blocks for thumb mode because that's the only way that you can do it inside of thumb mode.

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Um, in future lectures will look at the comparison of conditional execution vs Branching and then we'll look at Indian nous.