In almost all assembly books you’ll find some nice tricks to do fast multiplications. E.g. instead of “imul eax, ebx, 3” you can do “lea eax, [ebx+ebx*2]”Â (ignoring flag effects). It’s pretty clear how this works. But how can we speed up, say, a division by 3? This is quite important since division is still a really slow operation. If you never thought or heart about this problem before, get pen and paper and try a little bit. It’s an interesting problem.
Intel used some strange opcodes for the SSE3 instructions. All MMX/SSE opcodes use the 0x0f prefix (former “pop cs”). They soon noticed the the 0x0f area gets full, so they used the 0x66, 0xf2, 0xf3 prefix as modifiers. The basic rule is: