Memory-to-memory copy

Question

Is there a mechanism of efficiently simulating a memory-to-memory copy using x86 instructions?

I need to guarantee an instant in time when both the source address and the destination address point to equal values. I am currently using a loop (ie do { reg = *A; *B = reg; } while (reg != *A) ), but I'd like to optimize on that.

EDIT: Missed some important information: I'm copying pointers.

Answer 1

REP MOVSB（google it），还有WORD和DWORD版本，现在可能还有QWORDs