Hello, all

The Language Guide for Turbo Pascal 7.0 says:

Variable parameters (var parameters) are always
passed by reference--a pointer that points to the
actual storage location.
[...]
A pointer-type parameter is passed as two words
(a double word). The segment part is pushed
before the offset part so that the offset part
ends up at the lowest address.

I have written the following proceudre that adds its
first argument to the second:

procedure AtoB(a: byte; var b: byte);
begin asm
PUSH AX { store AX }
MOV DI, [BP+4] { store offset of b in DI }
MOV ES, [BP+2] { store segment of b in ES }
MOV AX, [BP+8] { store a in AX }
MOV [DI], AX { assign AX to a }
POP AX { restore AX }
end end;

Does not it show that the TP documentation is in er-
ror, and pointers are put on stack backwards?

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* Origin: nntps://fidonews.mine.nu - Lake Ylo - Finland (2:221/360.0)

I wrote:

procedure AtoB(a: byte; var b: byte);
begin asm
PUSH AX { store AX }
MOV DI, [BP+4] { store offset of b in DI }
MOV ES, [BP+2] { store segment of b in ES }
MOV AX, [BP+8] { store a in AX }
MOV [DI], AX { assign AX to a }
POP AX { restore AX }
end end;

Here is a fixed version, without redundant opera-
tions and with single-byte write:

procedure AtoB(a: byte; var b: byte);
begin asm
MOV ES, [BP+2] { store segment of b in ES }
MOV DI, [BP+4] { store offset of b in DI }
MOV AX, [BP+8] { store a in AX }
MOV [DI], AL { assign AL to a }
end end;

---
* Origin: nntps://fidonews.mine.nu - Lake Ylo - Finland (2:221/360.0)

I wrote:

Here is a fixed version, without redundant opera-
tions and with single-byte write:

procedure AtoB(a: byte; var b: byte);
begin asm
MOV ES, [BP+2] { store segment of b in ES }
MOV DI, [BP+4] { store offset of b in DI }
MOV AX, [BP+8] { store a in AX }
MOV [DI], AL { assign AX to a }
end end;

Problem solved. Here is the correct code in TP as-
sembly:

procedure AtoBRef(a: byte; var b: byte);
begin asm
MOV DI, [BP+4] { store offset of b in DI }
MOV ES, [BP+6] { store segment of b in ES }
MOV AX, [BP+8] { store a in AX }
MOV [ES:DI], AL { assign AX to a }
end end;

It works as advertised.

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* Origin: nntps://fidonews.mine.nu - Lake Ylo - Finland (2:221/360.0)