x86 Assembly Language Part-III

[Music] now let us discuss Advanced memory instructions so Advanced memory instructions is where we can actually see the power of the x86 instruction set so what good is a complex instruction set unless it gives us some instructions that make our life really really easy and so you know there has to be some

justification for the C in cisk so we'll see that uh with Advanced memory instructions so typically uh so so let me illustrate a typical case typically uh some instructions prove will prove to be useful uh if we look at certain common programming patterns so a typical programming pattern is that we move a large amount

of data like a large sequence of byes from one memory location to another memory location so instructions that help us in moving is long sequence of bytes from one memory location a to memory location B uh these are known as string instructions the string Instructions make special use of the EDI and ESI

registers as we had discussed in one of the earlier slides EDI contains the default destination and ESI contains the default source so the first instruction that we need to uh that we need to introduce in this category is the Lea instruction because the this is what will be used uh in U uh you know in the subsequent

discussion so this is very important it's like the Bedrock of all uh string instructions so Lea means load effective address and it is used to load an address into any register in particular the EDI and the ESI registers right so in general Lea can be used to load an address into any register but we are we will mostly be

interested in EDI and ESI in the later discussion but let's look at the generic case first so the standard format of Lea is this so the standard format of Lea is