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If I understood right - this is a "white box" reimplementation of the real Turbo Pascal, which uses the same algorithms and structures and control flow as the real one (and therefore should be bug-for-bug compatible) but is written in Pascal instead of assembly? That is, the "DX" argument there isn't actually passed in register DX, but it represents a function call in real Turbo Pascal that passed the same semantic contents in register DX?

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I don't know what a "white box" reimplementation is (white-box cryptography?) but I guess you meant a clean room implementation (https://en.wikipedia.org/wiki/Clean_room_design) which I believe this is not the case here (I am wild guessing though). For a clean room implementation you need at least two guys, one reverse engineer who writes down his findings and a guy who takes that information and reimplements the same functionality according to the information the reverse-engineer provides.

But you are right in that it uses the same algorithms, structures and control flow as the real Turbo Pascal and therefore should be bug-for-bug compatible but is written in Pascal instead of assembly.

Probably a poor choice of words, but I mean the opposite of a clean room reimplementation - it's one where the same person is looking at disassembly and writing the new implementation (i.e, the thing being reimplemented is a white box, not a black box).

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