[MUSIC]. Now I'll tell a little bit about, x86-64. I'm also going to show you how to do the swap example we saw in the previous video. But now, with, x86-64 insertions as opposed to the 32 bit. Instructions, okay? So x86-64 has 16 registers, okay? And just, just like I32, there's some registers that have special use, but there's a lot more general purpose registers. Like all of these registers here are only present in the 64 bit of x86. And also know that while these registers Are 64 bits wide. You can also access the lower 32 bits of them as a register, as well. For example, you know, eax, which is also present in IA-32, is the low order 32 bits of register. Rax in x86-64. Okay. So each look when we think about any existing registers to 64 bits plus adding eight new registers. and now the way we look at operands in 32 versus 64 bit modes the following Remember that we had, in, in I 32, look at move l. And l referred to moving 4 bytes worth of data. Now what we have in x86-64 is move q, it's a new type of data size that it's 8 bytes or 64 bits long. Okay. Now we also have other instructions, like addl that's presently in 32. Now we have addq. And then shift l and we can have shift q, and so on. So and also note that x86-64 can also use all the 32-bits instructions that 30, that generate 32-bit results. Okay? So ends like I showed you in the previous slide. We can use, we can reference the low order 32 bits of some 64 bit registers with the same name as we use in 32-bit ISA. And the, the high order 32 bits are set to zero. here's the example that we saw in a previous video. we had this swap function, that received two pointers, xp and xy, as parameters. And then it swaps the contents of these pointers, okay? remember that these two instructions here, what they were doing is they were reading The pointers that were stored in the stack because parameters in the I32, I, I32ABI passed by a, to stack. 'Kay, that's, that's one thing to note. And we've used all movl instructions. Because we're moving four bytes worth of data. Okay? So now, let's look at how this function, this piece of code will look like in 64 bits. Okay, bam, the first thing to notice, what we have, movl. Four of them. And also, note that we are passing the parameters. My registers. Okay, so directly as opposed to this text. So XP, the XP parameter is stored in register RDI. NYP is stored in register RSI, and these are 64 bit pointers because adversaries in 64, in access 664 are 64 bit. long. And look how interesting. Now we have only four instructions. We're no longer reading the parameters from the stack, which is a big advantage, right. So it's, it's much faster, don't have to store it to memory and read it back. And we have much fewer instructions. And now here, what we're doing is this first instruction gets the contents of the, the of xp, and stores it in a temporary variable. In this case t0, right? That happens to be mapped to adx. We get yp, it's contents, right? That's why we're using the parentheses here. We're just referencing the, the address. Storing the other temporary variable, t1, happens to be map, mapped to eax. And staying with just storing the temporary variable back into the pointers, and then we return. It's much simpler, right? And because the main reason it's simpler is because we don't have to, to use the stack at all. No stack operations required, and note that we still moved. 32 bits worth of data. Why is that? Well, because this integer's here. Happens to be four bytes long. Even though the pointer itself is 64 bits, the unit of data that it points to is a four byte. Integer. and, and we also use Move L tool. Because we're moving 4 bytes of data. We're still using the same type of instructions. Now suppose that we had long ends. Now if you're saying long ends here. We're saying that the union of data is 8 bytes here. 'Kay? So, even if there is a byte, now the move operation itself has to be eight bytes long. Remember that q refers to eight byte words. Okay? So and now since the long int is eight bytes as well, we have to use movq instructions. 'Kay? So, alright see you next time.