How to separate 32-bit address into high 16-bit address and

[leetow2003]

Look:
GATE STRUC
OFFSETL DW 0
SELECTOR DW 0
DCOUNT DB 0
GTYPE DB 0
OFFSETH DW 0
GATE ENDS

and I define a gate varible in LDT:
32GATEA GATE <Low 16-bbit BEGIN address, 10h, 0, 8CH, high 16-bit BEGIN address>

and I define a code segment:
CODESEG SEGMENT PARA USE32
ASSUME CS:CODESEG
BEGIN:
...
CODESEG ends

I want to know how to separate symbol BEGIN into Low 16-bbit BEGIN address and
high 16-bit BEGIN address in 32GATEA?Thank you.

[Tosi]

If your assembler supports it,

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High address = ((addr >> 16) & 0xFFFF)
Low address = (addr & 0xFFFF)

Otherwise, do it with code:

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mov edx, addr
mov eax, addr
shr eax, 16
and edx, 0xFFFF
; eax contains the high word, and edx contains the low word.

[Solar]

I have written next to zero functional lines of assembler in my life, so consider this a question rather than a suggestion.

But wouldn't it suffice to, say...

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mov eax, addr

...and then read the high word out of eh, and the low word out of el?

That's how I understood it so far. Am I wrong?

[qw]

...and then read the high word out of eh, and the low word out of el?

I guess you mean AH and AL? Those are the high- and low-order byte of AX, and AX is the low-order word of EAX, but there is no name for the high-order word of EAX. It is designed as this:

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+-------------------------------+
|              EAX              |
+ - - - - - - - + - - - - - - - +
|               |       AX      |
+ - - - - - - - + - - - + - - - +
|               |   AH  |   AL  |
+---------------+-------+-------+

[Solar]

Ah... right.

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mov eax, addr
mov low_word, ax
shr eax, 16
mov high_word, ax

That'd be it, no?

[qw]

That'd be it, no?

That's correct.

[Tosi]

I have been writing so much C (and C++ for school) code lately that my assembly has gotten inefficient.