FAQ (Всякие мелочи), страница 2

out dx,al ;ìëàäøèé áàéò ñ÷åò÷èêà

mov al,bh

out dx,al ;ñòàðøèé áàéò ñ÷åò÷èêà

Done:

pop dx ;âîññòàíîâèòü ðåãèñòðû

pop bx

pop ax

ret

Sound endp

Âûêëþ÷åíèå çâóêà:

No_Sound proc near

push ax

in al,61h ;ïîðò ÐÂ

and al,not 3 ;ñáðîñ áèòîâ 0-1

out 61h,al

pop ax

ret

No_Sound endp

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Q10: ×òî ëó÷øå - ñòàíäàðòíûå èëè óïðîùåííûå äèðåêòèâû îïðåäåëåíèÿ ñåãìåíòîâ?

A: Îäíîçíà÷íî ïðîùå - óïðîùåííûå. ×òî ëó÷øå - ðåøàåòñÿ èíäèâèäóàëüíî.

Èñïîëüçîâàíèå ñòàíäàðòíûõ äèðåêòèâ èìååò ñìûñë èëè â ïåäàãîãè÷åñêèõ

öåëÿõ, èëè ïðè íàëè÷èè ïðè÷èí, òðåáóþùèõ èñïîëüçîâàíèÿ èìåííî ñòàíäàðòíûõ

äèðåêòèâ. Íàïðèìåð, íåîáõîäèìîñòü èñïîëüçîâàíèÿ ñïåöèàëüíûõ èìåí

ñåãìåíòîâ, ñïåöèàëüíûõ àòðèáóòîâ è îñîáîé ãðóïïèðîâêè. Ïîñëåäíåå

îïÿòü-òàêè âîâñå íå îçíà÷àåò, ÷òî óïðîùåííûå äèðåêòèâû íå ìîãóò áûòü

èñïîëüçîâàíû. Íàïðèìåð:

.MODEL LARGE

MyGroup group MySpecialSeg,$LibTable

MySpecialSeg segment word public use16 'DATA'

...

ends

$LibTable segment para common use16 'DATA'

...

ends

.DATA

.CODE

end

Ïîýòîìó âïîëíå ðàçóìíûì âèäèòñÿ èñïîëüçîâàíèå óïðîùåííûõ äèðåêòèâ,

ñîâìåùåííîå (ïðè íåîáõîäèìîñòè) ñ èñïîëüçîâàíèåì ñòàíäàðòíûõ.

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Q11: Äëÿ ÷åãî íóæíà êîìàíäà LEA. Òî æå ñàìîå ìîæåò è OFFSET, äà è Tasm çàìåíÿåò

LEA íà MOV...OFFSET.

A: MOV...OFFSET êîðî÷å LEA, ïîýòîìó â ðåæèìå SMART tasm çàìåíÿåò LEA íà MOV

äëÿ òåõ ñëó÷àåâ, êîãäà ýòî âîçìîæíî:

lea di,Array

mov di,offset Array

Íî òàêàÿ çàìåíà âîçìîæíà íå âñåãäà:

lea di,Array[si+bx.FieldName]

Ëîãèêà ðàáîòû LEA â äàííîì ñëó÷àå ýêâèâàëåíòíà òàêîìó ôðàãìåíòó:

mov di,offset Array

add di,si

add di,bx

add di,FieldName

Ðåçóëüòàò ýòîãî ôðàãìåíòà íå ìîæåò áûòü âû÷èñëåí íà ýòàïå êîìïèëÿöèè

èç-çà íåèçâåñòíûõ âåëè÷èí, à ñëåäîâàòåëüíî, LEA â äàííîì ñëó÷àå íå ìîæåò

áûòü çàìåíåíà êîìàíäîé MOV...OFFSET

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Q12: mov ax,@data

mov ds,ax

Îòêóäà ïðîãðàììà óçíàåò àäðåñ ñåãìåíòà? Ïîñëå êîìïèëÿöèè ñòîèò mov ax,1.

À â îòëàä÷èêå ïîÿâëÿåòñÿ ñðàçó íóæíûé àäðåñ: mov ax,140Fh

Êòî åãî òóäà ïðîïèñûâàåò?

A: Ò.ê. EXE ìîæåò áûòü çàãðóæåí ïî ðàçëè÷íûì àäðåñàì, âìåñòî ÿâíûõ çíà÷åíèé

cåãìåíòîâ â EXE óêàçàíû íîìåðà 16-áàéòíûõ ïàðàãðàôîâ [0...FFFF] ýòèõ

cåãìåíòîâ, íà÷èíàÿ îò íà÷àëà îáðàçà EXE. Çàãðóç÷èê, ïîñëå ñ÷èòûâàíèÿ îáðàçà

EXE â ïàìÿòü, èñïîëüçóÿ èíôîðìàöèþ â çàãîëîâêå EXE, íàõîäèò ññûëêè íà

ÿâíûå çíà÷åíèÿ ñåãìåíòîâ è ïðèáàâëÿåò ê çíà÷åíèþ ïàðàãðàôà, óêàçàííîå

íåïîñðåäñòâåííî â êîìàíäå, ðåàëüíîå çíà÷åíèå ñåãìåíòà, íà÷èíàÿ ñ êîòîðîãî

çàãðóæåí EXE.

Íàïðèìåð, îáðàç EXE ñ÷èòàí â ïàìÿòü, íà÷èíàÿ ñ àäðåñà 140Eh:0 Ïîñëå

êîððåêòèðîâêè çíà÷åíèé ñåãìåíòîâ âìåñòî mov ax,1 ïîëó÷àåòñÿ mov ax,140F

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Q13: Êàê ñäåëàòü COM ñ îòëàäî÷íîé èíôîðìàöèåé, ïîíèìàåìîé TD ?

A: comdbg.bat TEST

tasm /zi %1

tlink /v %1,%1,,,

tdstrip -s -c %1.exe

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Q14: Íå ïîëó÷àåòñÿ! COM åñòü, TDS åñòü, à TD îòëàäî÷íóþ èíôîðìàöèþ íå âèäèò:

"Program has no symbol table"

A: Ó TDS âðåìÿ ìåíüøå, ÷åì ó COM - òàêîå áûâàåò â Âèíäå.

Âîñïîëüçóéòåñü óòèëèòîé touch èç NWDOS (â MS DOS îíà ïîõóæå)

touch %1.tds

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Q15: Êàê ðàñ÷èòàòü êîëè÷åñòâî ïàìÿòè, íåîáõîäèìîå äëÿ ðåçèäåíòà?

A: FirstFreeByteSeg - PspSeg + ((FirstFreeByteOffs+15) div 16)

Resident macro FirstFreeByteSeg,FirstFreeByteOffs

mov dx,FirstFreeByteSeg

sub dx,[PspSeg]

mov ax,FirstFreeByteOffs

dec ax

shr ax,4

inc ax

add dx,ax

mov ah,31h

mov al,[ErrorLevel]

int 21h

endm

Resident seg Install,<offset Install>

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Q16: Íå ìîãó çàïóñòèòü äî÷åðíþþ çàäà÷ó ôóíêöèåé 4Bh

Q17: Íå âûäåëÿåòñÿ ïàìÿòü ïî ôóíêöèè 48h

A: Íåò ñâîáîäíîé ïàìÿòè.

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Q18: Äà âðîäå âñå åñòü, ïî÷åìó íå âûäåëÿåò-òî?

A: Äà ïîòîìó ÷òî îíà óæå òåáå âûäåëåíà, òåïåðü åå îñòàëîñü òîëüêî ñæàòü.

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Q19: Êàê ñæàòü áëîê ïàìÿòè, çàíèìàåìûé ïðîãðàììîé?

A: Ñæèìàòü åå ñëåäóåò ÷åðåç ôóíêöèþ DOS 4Ah. Àëãîðèòì òîò æå, ÷òî è ó

ìàêðîñà Resident:

ShrinkMem macro FreeSeg,FreeOffs

mov bx,FreeSeg

sub bx,[PspSeg]

mov ax,FreeOffs

dec ax

shr ax,4

inc ax

add bx,ax

mov ah,4Ah

mov es,[PspSeg]

int 21h

endm

ShrinkMem <seg stack>,<(size stack)+1>

 ñëó÷àå ïîëíîãî/äîïîëíèòåëüíîãî ðó÷íîãî îáúÿâëåíèÿ ñåãìåíòîâ è èõ îñîáîãî

óïîðÿäî÷èâàíèÿ íåîáõîäèìî óêàçàòü èìÿ ïîñëåäíåãî ñåãìåíòà.

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Q20: À ÷òî çà êîìàíäà òàêàÿ rdtsc?

A: read tsc - Read Time Stamp Counter. ×èòàåò ðåãèñòð tsc, ïðîùå ãîâîðÿ

âîçâðàùàåò â edx:eax êîëè÷åñòâî òàêòîâ ñ ìîìåíòà ïîñëåäíåãî ñáðîñà

ïðîöåññîðà. Îïêîä - 0F 31, êîìàíäà ïîÿâèëàñü íà ïðîöåññîðàõ Pentium (è

òî íå íà âñåõ.)

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Q21:. È åùå, ðàññêàæèòå ðóññêèì ÿçûêîì, ÷òî òàêîå ðåêóðñèÿ (íèêîãäà íå

ñòàëêèâàëñÿ!)?

A: Âûçîâ ôóíêöèåé ñàìîé ñåáÿ.

Q: Ïðèìåð÷èê ïðèâåòñòâóåòñÿ.

A: Êëàññè÷åñêèé ïðèìåð - âû÷èñëåíèå ôàêòîðèàëà:

..model farstack small, pascal

.386

locals @@

..stack 2048

..code

Factorial PROC ; function factorial(@@N:Word):DWord;

arg @@N:word ; begin

mov ax,@@N

cmp ax,1 ; if (@@N=1) or (@@N=0) then

ja @@calc

mov ax,1 ; factorial:=1

xor dx,dx

ret

@@calc:

dec ax ; else

push ax

call Factorial ; factorial := factorial(@@N-1)

mul @@N ; * @@N;

ret ; end;

endp

MAIN PROC

.startup

push 4

call Factorial

.exit

ENDP

end MAIN

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Q22: Ðàññêàæèòå ïðî ñîïðîöåññîð, êàê åãî èñïîëüçîâàòü?

A: Âîò òåáå ïðèìåð ïðîãðàììû ñ êîììåíòàðèÿìè:

..model tiny

..code

..386 ; ïðèâû÷êà :)

..387 ; èñïîëüçîâàíèå ñîïðîöà

..startup