请注意，mptr是按8字节边界划分颗粒度的，而这一位置不是。
Note that the MPTR, not this slot, is grained on an 8 byte boundary. The flags are as follows.
优化的传输是128的整数倍，它们都在128字节边界上对齐。
Optimal transfers are multiples of 128 bytes that are on 128-byte boundaries.
存储这样的值则更为困难，所以如果可能，最好永远不要使用跨16字节边界的值。
Storing such values is even more difficult, so it is best to never use values that cross 16-byte boundaries.
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