计算段:与绝对地址的偏移量 [英] Calculate Segment:Offset from absolute address

问题描述

我可以将地址Segment:Offset计算为Segment * 0x10 + Offset.但是我该如何计算相反的结果呢?

I can calculate an address Segment:Offset as Segment * 0x10 + Offset. But how do I calculate the opposite?

例如如何从0xF4170到F400:0170以及从0xACF04到ABCD:1234?

E.g. how do I get from 0xF4170 to F400:0170 and from 0xACF04 to ABCD:1234?

推荐答案

由于多个Segment:Offset对可以映射到相同的对，因此您需要具有基数或起始偏移量以及线性地址线性地址.

You would be required to have either the base or the offset to start with, along with the linear address, as multiple Segment:Offset pairs can map to the same linear address.

因此，如果我们有段0xF400和线性地址0xF4170，则得到的偏移量为0xF4170 - (0xF400 << 4)，即0x170.

so if we have the segment 0xF400 and the linear address 0xF4170, we get the offset being 0xF4170 - (0xF400 << 4) which is 0x170.

仅知道线性地址就没有唯一的解决方案，因此您必须选择一种约定，将20位地址拆分为16字节对齐的seg部分和字节偏移量.一种可能的功能是:

Doing this with only knowing the linear address doesn't have a unique solution, so you have to choose a convention for splitting a 20-bit address into a 16-byte-aligned seg part and a byte offset. One possible function is this:

• Segement = linear >> 4(前16位)
• offset = linear & 0x0F(低4位)

• Segement = linear >> 4 (top 16 bits)
• offset = linear & 0x0F (low 4 bits)

您可以选择12:8位的规范格式，从而为将来扩展更宽的线性地址留出空间.

You might choose a canonical form with 12:8 bits, leaving room for future expansion with wider linear addresses.

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