DOS ain't dead - Error in XMS specification?

Error in XMS specification? - movp (Developers)

posted by ecm , Düsseldorf, Germany, 09.01.2026, 22:07

Here's another piece of code explaining the overlap check for moving "down" (DF=1). If S < D and S + L > D then we are overlapping in the way requiring a backwards move.

cmp ax, dx ; source above destination ? ja .up ; yes, move up (forwards) --> je .return ; same, no need to move --> push ax add ax, cx ; (expected not to carry) cmp ax, dx ; end of source is above destination ? pop ax ja .down ; yes, move from top down --> ; Here, the end of source is below-or-equal the destination, ; so they do not overlap. In this case we prefer moving up.

---
l

Post reply

Complete thread:

Error in XMS specification? - ecm, 27.04.2019, 16:16 (Developers)
- Error in XMS specification? - Oso2k, 27.04.2019, 20:20
  - Error in XMS specification? - ecm, 27.04.2019, 21:40
- Error in XMS specification? - emu2 - ecm, 09.01.2026, 21:53
  - Error in XMS specification? - movp - ecm, 09.01.2026, 22:07
    - Error in XMS specification? - movp - bretjohn, 10.01.2026, 00:18