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|    alt.os.development    |    Operating system development chatter    |    4,255 messages    |
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|    Message 3,335 of 4,255    |
|    mutazilah@gmail.com to Joe Monk    |
|    Re: segmentation    |
|    22 Oct 22 13:19:56    |
      From: muta...@gmail.com              On Sunday, October 23, 2022 at 4:15:51 AM UTC+8, Joe Monk wrote:       > > > https://en.wikipedia.org/wiki/Far_pointer        > > It is possible if you manipulate the segment.       > "For example, in an Intel 8086, as well as in later processors running       16-bit code, a far pointer has two parts: a 16-bit segment value, and a 16-bit       offset value. A linear address is obtained by shifting the binary segment       value four times to the left,        and then adding the offset value. Hence the effective address is 20 bits       (actually 21-bit, which led to the address wraparound and the Gate A20). There       can be up to 4096 different segment-offset address pairs pointing to one       physical address. To compare        two far pointers, they must first be converted (normalized) to their 20-bit       linear representation."        >        > char far *p =(char far *)0x55550005;        > char far *q =(char far *)0x53332225;        >        > "Physical Address = (value of segment register) * 0x10 + (value of offset).        > Location pointed to by pointer 'p' is : 0x5555 * 0x10 + 0x0005 = 0x55555        > Location pointed to by pointer 'q' is : 0x5333 * 0x10 + 0x2225 = 0x55555        > So, p and q both point to the same location 0x55555."        >        > The same is true regardless of the offset.               Not sure if we're talking cross-purposes here.              I didn't invent the term "huge pointer". It has a meaning       distinct from "far pointer".              BFN. Paul.              --- SoupGate-Win32 v1.05        * Origin: you cannot sedate... all the things you hate (1:229/2)    |
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