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TurboCUser'sGuide:

EmbeddedAssemblyLanguage.PartIBasicPrinciples

BASM.DOCisononlinefilethattellsyouhowtousetheTurboC++builtininlineassembler(BASM)toincludeassemblylanguageroutinesinyourCandC++programswithoutanyneedforaseparateassembler.Suchassemblylanguageroutinesarecalledinlineassembly,becausetheyarecompiledrightalongwithyourCroutines,ratherthanbeingassembledseparately,thenlinkedtogetherwithmodulesproducedbytheCcompiler.

TurboC++letsyouwriteassemblylanguagecoderightinsideyourCandC++programs.Thisisknownasinlineassemblyandhascertainrestrictions.

ItcannotuseassemblermacrosItcannothandle80386or80486instructionsItdoesnotpermitIdealmodesyntaxItallowsonlyalimitedsetofassemblerdirectives

Toinvoketheinlineassembler,youneedonlyusethekeywordasmtointroduceaninlineassemblylanguageinstruction.Theformatis

asmopcodeoperands

whereopcodeisavalid80x86instruction,andoperandscontainstheoperand(s)acceptabletotheopcode,andcanreferenceCconstants,variables,andlabels.

Toincludeanumberofasmstatements,surroundthemwithbraces:Theinitialbracemustappearonthesamelineastheasmkeyword.

Semicolonsarenotusedtostartcomments(astheyareinTASM).Whencommentingasmstatements,useCstylecomments,likethis:

asmmovax,ds/*ThiscommentisOK*/asm{popaxpopdsiret}/*Thisislegaltoo*/asmpushdsTHISCOMMENTISINVALID!!

Theassemblylanguageportionofthestatementiscopiedstraighttotheoutput,embeddedintheassemblylanguagethatTurboC++isgeneratingfromyourCorC++instructions.AnyCsymbolsarereplacedwithappropriateassemblylanguageequivalents.

Becausetheinlineassemblyfacilityisnotacompleteassembler,itmaynotacceptsomeassemblylanguageconstructs.Ifthishappens,TurboC++willissueanerrormessage.Youthenhavetwochoices.Youcansimplifyyourinlineassemblylanguagecodesothattheassemblerwillacceptit,oryoucanuseanexternalassemblersuchasTASM.However,TASMmightnotidentifythelocationoferrors,sincetheoriginalCsourcelinenumberislost.

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Youcanincludeanyofthe80x86instructionopcodesasOpcodesinlineassemblystatements.TherearefourclassesofinstructionsallowedbytheTurboC++compiler:

normalinstructionstheregular80x86opcodesetstringinstructionsspecialstringhandlingcodesjumpinstructionsvariousjumpopcodesassemblydirectivesdataallocationanddefinition

Notethatalloperandsareallowedbythecompiler,eveniftheyareerroneousordisallowedbytheassembler.Theexactformatoftheoperandsisnotenforcedbythecompiler.

Prefixes

Thefollowingprefixescanbeused:

lockrepreperepnerepnzrepz

JumpInstructions

Jumpinstructionsaretreatedspecially.Sincealabelcannotbeincludedontheinstructionitself,jumpsmustgotoClabels.Theallowedjumpinstructionsaregiveninthenexttable.

ja jge jnc jns loop

jae jl jne jnz loope

jb jle jng jo loopne

jbe jmp jnge jp loopnz

jc jna jnl jpe loopz

jcxz jnae jnle jpo je

jnb jno js jg jnbe

jnp jz

AssemblyDirectives

ThefollowingassemblydirectivesareallowedinTurboC++inlineassemblystatements:

db dd dw extrn

CSymbols

YoucanuseCsymbolsinyourasmstatementsTurboC++Inlineassemblyautomaticallyconvertsthemtoappropriateassemblyreferencestodatalanguageoperandsandappendsunderscoresontoandfunctionsidentifiernames.Youcanuseanysymbol,includingautomatic(local)variables,registervariables,andfunctionparameters.

Ingeneral,youcanuseaCsymbolinanypositionwhereanaddressoperandwouldbelegal.Of

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course,youcanusearegistervariablewhereveraregisterwouldbealegaloperand.Iftheassemblerencountersanidentifierwhileparsingtheoperandsofaninlineassemblyinstruction,itsearchesfortheidentifierintheCsymboltable.Thenamesofthe80x86registersareexcludedfromthissearch.Eitheruppercaseorlowercaseformsoftheregisternamescanbeused.

InlineAssemblyandRegisterVariables

InlineassemblycodecanfreelyuseSIorDIasscratchregisters.IfyouuseSIorDIininlineassemblycode,thecompilerwon'tusetheseregistersforregistervariables.

Whenprogramming,youdon'tneedtobeconcernedwiththeexactoffsetsoflocalvariables.Simplyusingthenamewillincludethecorrectoffsets.However,itmaybenecessarytoincludeappropriateWORDPTR,BYTEPTR,orothersizeoverridesonassemblyinstruction.ADWORDPTRoverrideisneededonLESorindirectfarcallinstructions.

ExamplesofInlineAssemblyLanguage

1.ExampleofwindowscrollingroutineswithkeyboardIO.

#include

voidscreen(void);

voidscroll(void);

voidget_char(void);

charchar_in;//variabledefs

unsignedcharrow,col,row_up,row_down,col_up,col_down;

voidmain()

{

row=0;

col=0;

row_up=3;//definea10lineby40col

row_down=13;//windowforscrolling

col_up=20;

col_down=60;

screen();//erasethescreen

scroll();//scrollthescreen

get_char();//getchartoterminate...

}

voidscreen()

{asm{

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movcx,50h/*80interations*/

}

disp_loop:

asm{

movah,02h/*cursorposition*/

movbh,00h/*BIOScall*/

movdh,row

anddh,0Fh/*limit32lines*/

movrow,dh/*restorerowvalue*/

movdl,col

int10h

incrow/*incrrow,colptrs*/

inccol

movah,02h/*DOScharoutput*/

movdl,'x'/*outputtheXchar*/

int21h

loopdisp_loop/*loopuntildone*/

}

}

//............................................

voidscroll()

{asm{

movah,06h/*BIOSscrollfunction*/

moval,10h/*16lines*/

movbh,00h

movch,row_up/*setwindowlimits*/

movcl,col_up

movdh,row_down

movdl,col_down

int10h

}

}

//............................................

voidget_char()

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{asm{

movah,02h/*cursorposBIOScall*/

movbh,00h

movdh,06d

movdl,25d

int10h

movah,02h/*DOScharoutputcall*/

movdl,'?'

int21h

movah,01h/*keyboardin,noecho*/

int21h

}

}

2.ArrayManipulation

#include

#include

voidmain()

{

intarray1[64],array2[64],i,*a1,*a2;

charch;

for(i=1;i

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loopx

}

}

for(i=0;i