Question

Is it possible to access to a single byte in a mmx register, like a array?
I’ve this code:

movq mm1,vector1
movq mm2,vector2
psubw mm1,mm2

I want to put mm1[1],mm1[2],mm1[3]….into c++ vars, like:

int a,b=0;
mov a,mm1[1]
mov b,mm1[2]

Thanks.

Answer 1

Yes, it is possible.

I can show the code for SSE2 for c++, but is similar for MMX :

__m128i a;
unsigned char *p = (unsigned char*) &a;
// access bytes pointed by pointer p