使用这些操作前，需要提供一个值和将要进行操作的位掩码，如清单 4 所示。
You provide a value and the bitmask upon which the operation is to be performed, as shown in Listing 4.
要加载跨越16字节边界的值会十分困难，因为必须要将其存储到两个寄存器，进行移位然后再对它们进行掩码和组合。
To load a value which crosses a 16-byte boundary is even more difficult, as you would actually have to load it into two registers, shift them, and then mask and combine them.
进制的常量通常都用作掩码或特殊位的值。
Hexadecimal constants are commonly used as masks or specific bit values.
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