Cheat Engine

[Zazary]

Hi everyone, I'm just learning and please explain how to extract numbers from xmm? Here is an example of xmm0: 1522.66 - 56.23 - 68.30 - 0.00. I want to extract Y and do movss xmm0, [allocaddress], and is it possible to extract even more values? Also, how do I determine the axes? I only figured out that X is 1522.66, Z is 56.23, and Y is 68.30. Do I need to determine this myself, or is there a more accurate way? (I would like examples as I have been trying to understand xmm for 3 days and still can't figure it out.)

[ParkourPenguin]

XMM registers store 16 bytes of data. This can be integer data of various sizes, 4 floats, or 2 doubles. In this case, that's 4 floats.

Vector operations on xmm registers operate on all the values at the same time. e.g. `movups` (move unaligned packed singles) moves 4 floats at once, `addps` (add packed singles) adds 4 floats to 4 other floats at the same time, etc.
Scalar operations on xmm registers operate on the first value in the xmm register. e.g. `movss` (move scalar single) moves 1 float, `addss` (add scalar single) adds 1 float to 1 other float, etc. Sometimes these operations zero the other values in the xmm register to eliminate false dependencies (e.g. `movss` when moving from a memory location into an xmm register).

Operating on individual elements of a packed xmm register is a little tricky. Compilers will shuffle values in an xmm register as needed- e.g. `shufps` for floats. For humans writing assembly by hand, it's typically easier to store it into memory and operate on the floats individually using scalar operations.
https://forum.cheatengine.org/viewtopic.php?p=5790301

X, Y, and Z are arbitrary names given to axes. They can mean different things to different people. Some people might think differently from you and say Y is 56.23 and Z is 68.30.

[luigimud]

I think I understand it better now thanks to you. So, if I want to work with just the Y value (68.30 in my example), I should probably use a combination of movaps to move the entire xmm register into memory, then access the specific float I need, correct?

To confirm my understanding: shufps xmm0, xmm0, 0x4E, This instruction shuffles the values in xmm0. The immediate value 0x4E is a control byte that specifies how to shuffle the values. In this case, it moves the third float to the first position.

movss [allocaddress], xmm0: This moves the first float in xmm0 (which is now 68.30) to the memory address allocaddress.

What I came up with to extract the Y value:
; Allocate memory for storing the xmm register values
alloc(mem, 16)
registersymbol(mem)

; Move the entire xmm0 register to memory
movaps [mem], xmm0

; Now move the Y value (68.30) into xmm1
movss xmm1, [mem+8]

Is this the right approach? Also, if I want to put this Y value back into xmm0, should I use the same method, just reversed?

[ParkourPenguin]