多字节NOP指令可用于循环体之前的对齐， 来提高程序的性能， http://www.felixcloutier.com/x86/NOP.html
对齐如下表：
Length Assembly Byte Sequence
------- ------------------------------------------ --------------------------
1 byte nop 90
2 bytes 66 nop 66 90
3 bytes nop dword ptr [eax] 0F 1F 00
4 bytes nop dword ptr [eax + 00h] 0F 1F 40 00
5 bytes nop dword ptr [eax + eax*1 + 00h] 0F 1F 44 00 00
6 bytes 66 nop word ptr [eax + eax*1 + 00h] 66 0F 1F 44 00 00
7 bytes nop dword ptr [eax + 00000000h] 0F 1F 80 00 00 00 00
8 bytes nop dword ptr [eax + eax*1 + 00000000h] 0F 1F 84 00 00 00 00 00
9 bytes 66 nop word ptr [eax + eax*1 + 00000000h] 66 0F 1F 84 00 00 00 00 00