What to use in TASM for MASM's LOWWORD()?

[japheth]

Hi,

I'm currently converting a source into TASM 4.1/5.0 and cannot figure out how to convert MASM:

     dw LOWWORD(offset xxx)

into TASM. LOW() is supported in TASM, but returns a BYTE only, what returns a WORD?

Regards

Japheth

[GregL]

Japheth,

Here are some examples from The Paradigm Assembler User's Guide. The Paradigm Assembler is based on TASM 5.0 and not much, if anything, is different. It is a very good guide for TASM.

Code Select Expand


; IDEAL Mode
big  DD 12345678h
MOV  ax,[WORD big]                    ;ax=5678h
MOV  al,[BYTE PTR big]                ;al=78h
MOV  ax,[WORD HIGH big]               ;ax=1234h
MOV  ax,[WORD LOW big]                ;ax=5670h
MOV  al,[BYTE LOW WORD HIGH big]      ;al = 3rd byte of big = 34h

; MASM Mode
MOV  ax,2 PTR big                     ;ax=5678h
MOV  ax,WORD PTR big                  ;ax=5678h (WORD has value 2)


[japheth]

thanks a lot for this link! TASM docs are hard to find.

From the documentation I can see that the Paradigm Assembler (and TASM) supports the "SMALL" operator, which seemed to be an replacement for LOWWORD. But my efforts using it to get the low word of an offset *directly* weren't successful.

This is my test case:

Code Select Expand


.386

_TEXT segment use32 public

db 13210h dup (?)
xxx db 0

    mov ax, small offset xxx  ;I want 3210h in AX!

_TEXT ends

END


I tried some dozen variants, but none worked.

[Synfire]

Code Select Expand


.386

_TEXT segment use32 public

db 13210h dup (?)
xxx db 0

    mov ax, small offset xxx  ;I want 3210h in AX!

_TEXT ends

END


Wouldn't it be like this...

Code Select Expand


.386

_TEXT segment use32 public

www dw 013210h
bbb db 0, 1, 32h, 10h ; same thing as above

ASSUME ds:_TEXT

mov ax, [www]
mov cx, [bbb]

_TEXT ends

END


I haven't coded TASM in MANY MANY years but your xxx was in the wrong spot afiak, and you need to set DS to the section in which the data is actually in (in this instance it's the same as the code. Enclosing in brackets should give you access to the value at that address, and since you are moving into the AX register, you shouldn't need to typecast it since the assembler knows the size of AX and will insert that ammount from that memory location. Let me know if I'm wrong, if so I'll hunt down my TASM 5.0 disks and install it and find out where I went wrong.

Regards,
Bryant Keller

[japheth]

> Wouldn't it be like this...

> ASSUME ds:_TEXT
> mov ax, [www]
> mov cx, [bbb]

No, this loads something from memory to registers, but the LOWWORD() operator just loads part of an address into a register (which does *not* access memory).

[GregL]

Japheth,

Are you using IDEAL mode or not?

[japheth]

Hi Greg,

> Are you using IDEAL mode or not?

No, since one must be able to assemble the source by either MASM or TASM.

[P1]

LOW() is supported in TASM, but returns a BYTE only, what returns a WORD?

Can you use a size over ride on this operator?

I don't use TASM, but the question seemed to make sense.

Regards,  P1  :8)

[japheth]

> Can you use a size over ride on this operator?

Yes, both variants are accepted:

Code Select Expand


    dw word ptr LOW(offset xxx)

and

    dw LOW(word ptr xxx)


but also in both cases the expression evaluates to 0010h, not 3210h. And replacing LOW by SMALL gives errors.

[P1]

In the Old days, I would just mask off what I did not want.

Nibbles and Bits, food for that old dog programmer.

Regards,  P1  :8)