CODEWITHSUNDEEP
assemblymmx
user2059300
user2059300

Reputation: 361

x86_64 ASM: Alternative to movq?

Is there an alternate way to put a qword in an mmx register?

For example, in this code snippet:

db random 0xaa,0xaa,0xaa,0xaa,0xaa,0xaa,0xaa,0xaa
run:
    movq mm2, [rel random]

I can now work with that as a qword 0xaaaaaaaaaaaaaaaa and do pxor etc with it. Is there some other way I could put that data in the register? Maybe by pushing/popping to it?

Upvotes: 0

Views: 519

Answers (1)

Jester
Jester

Reputation: 58782

No idea why you want to do this, but you can avoid movq if you zero the register and then bring in the value using some operation, such as:

pxor mm2, mm2
pxor mm2, [rel random]

Alternatively, you can load the words using pinsrw:

pinsrw mm2, [rel random], 0
pinsrw mm2, [rel random + 2], 1
pinsrw mm2, [rel random + 4], 2
pinsrw mm2, [rel random + 6], 3

This approach also works in reverse using pextrw but have to go through a general purpose register:

pextrw eax, mm2, 0
mov [rel random], ax
pextrw eax, mm2, 1
mov [rel random + 2], ax
pextrw eax, mm2, 2
mov [rel random + 4], ax
pextrw eax, mm2, 3
mov [rel random + 6], ax

If only movq must be avoided but maskmovq can be used then you can do:

pcmpeqb mm1, mm1
lea rdi, [rel random]
maskmovq mm2, mm1

Upvotes: 3

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