单片机外文翻译汇编语言的艺术译文 英文.docx

单片机外文翻译汇编语言的艺术译文 英文.docx

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单片机外文翻译汇编语言的艺术译文英文

TheArtofAssemblyLanguage

1.What'sWrongWithAssemblyLanguage？

2.What'sRightWithAssemblyLanguage？

1.What'sWrongWithAssemblyLanguage

Assemblylanguagehasaprettybadreputation.Thecommonimpressionaboutassemblylanguage

programmerstodayisthattheyareallhackersormisguidedindividualswhoneedenlightenment.

Herearethereasonspeoplegivefornotusingassembly:

•

（1）Assemblyishardtolearn.

•

（2）Assemblyishardtoreadandunderstand.

•（3）Assemblyishardtodebug.

•（4）Assemblyishardtomaintain.

•（5）Assemblyishardtowrite.

•（6）Assemblylanguageprogrammingistimeconsuming.

•（7）Improvedcompilertechnologyhaseliminatedtheneedforassemblylanguage.

•（8）Today,machinesaresofastthatwenolongerneedtouseassembly.

•（9）Ifyouneedmorespeed,youshoulduseabetteralgorithmratherthanswitchtoassemblylanguage.

•（10）Machineshavesomuchmemorytoday,savingspaceusingassemblyisnotimportant.

•（11）Assemblylanguageisnotportable.

Thesearesomestrongstatementsindeed!

Giventhatthisisabookwhichteachesassemblylanguageprogramming,writtenforcollegelevelstudents,writtenbysomeonewhoappearstoknowwhathe'stalkingabout,yournaturaltendencyistobelievesomethingifitappearsinprint.Havingjustreadtheabove,you'restartingtoassumethatassemblymustbeprettybad.Andthat,dearfriend,iseightypercentofwhat'swrongwithassemblylanguage.Thatis,peopledevelopsomeverystrongmisconceptionsaboutassemblylanguagebasedonwhatthey'veheardfromfriends,instructors,articles,andbooks.Oh,assemblylanguageiscertainlynotperfect.Itdoeshavemanyrealfaults.Thosefaults,however,areblowncompletelyoutofproportionbythoseunfamiliarwithassemblylanguage.Thenexttimesomeonestartspreachingabouttheevilsofassemblylanguage,ask,"howmanyyearsofassemblylanguageprogrammingexperiencedoyouhave?

"Ofcourseassemblyishardtounderstandifyoudon'tknowit.Itissurprisinghowmanypeoplearewillingtospeakoutagainstassemblylanguagebasedonlyonconversationsthey'vehadorarticlesthey'veread.

Assemblylanguageusersalsousehighlevellanguages（HLLs）;assembly'smostoutspokenopponentsrarelyuseanythingbutHLLs.Whowouldyoubelieve,anexpertwellversedinbothtypesofprogramminglanguagesorsomeonewhohasnevertakenthetimetolearnassemblylanguageanddevelopanhonestopinionofitscapabilities?

Inaconversationwithsomeone,Iwouldgotogreatlengthstoaddresseachoftheaboveissues.Indeed,inaroughdraftofthischapterIspentabouttenpagesexplainingwhatiswrongwitheachoftheabovestatements.However,thisbookislongenoughandIfeltthatverylittlewasgained

bygoingonandonaboutthesepoints.Nonetheless,abriefrebuttaltoeachoftheabovepointsisinorder,iffornootherreasonthantokeepyoufromthinkingthereisn'tadecentdefenseforthesestatements.

Assemblyishardtolearn.Soisanylanguageyoudon'talreadyknow.Trylearning（reallylearning）APL,Prolog,orSmalltalksometime.OnceyoulearnPascal,learninganotherlanguagelikeC,BASIC,FORTRAN,Modula-2,orAdaisfairlyeasybecausetheselanguagesarequitesimilartoPascal.Ontheotherhand,learningadissimilarlanguagelikePrologisnotsosimple.AssemblylanguageisalsoquitedifferentfromPascal.ItwillbealittlehardertolearnthanoneoftheotherPascal-likelanguages.However,learningassemblyisn'tmuchmoredifficultthanlearningyourfirstprogramminglanguage.

Assemblyishardtoreadandunderstand.Itsureis,ifyoudon'tknowit.Mostpeoplewhomakethisstatementsimplydon'tknowassembly.Ofcourse,it'sveryeasytowriteimpossible-to-readassemblylanguageprograms.It'salsoquiteeasytowriteimpossible-to-readC,Prolog,andAPLprograms.Withexperience,youwillfindassemblyaseasytoreadasotherlanguages.

Assemblyishardtodebug.Sameargumentasabove.Ifyoudon'thavemuchexperiencedebuggingassemblylanguageprograms,it'sgoingtobehardtodebugthem.RememberwhatitwaslikefindingbugsinyourfirstPascal（orotherHLL）programs?

Anytimeyoulearnanewprogramminglanguageyou'llhaveproblemsdebuggingprogramsinthatlanguageuntilyougain

experience.

Assemblyishardtomaintain.Cprogramsarehardtomaintain.Indeed,programsarehardtomaintainperiod.Inexperiencedassemblylanguageprogrammerstendtowritehardtomaintainprograms.Writingmaintainableprogramsisn'tatalent.It'saskillyoudevelopthroughexperience.

Assemblylanguageishard.Thisstatementactuallyhasaringoftruthtoit.Forthelongesttimeassemblylanguageprogrammerswrotetheirprogramscompletelyfromscratch,often"re-inventingthewheel."HLLprogrammers,especiallyC,Ada,andModula-2programmers,havelongenjoyedthebenefitsofastandardlibrarypackagewhichsolvesmanycommonprogrammingproblems.Assemblylanguageprogrammers,ontheotherhand,havebeenknowntorewriteanintegeroutputroutineeverytimetheyneedone.Thisbookdoesnottakethatapproach.Instead,ittakesadvantageofsomeworkdoneattheUniversityofCalifornia,Riverside:

theUCRStandardLibraryfor80x86AssemblyLanguageProgrammers.ThesesubroutinessimplifyassemblylanguagejustastheCstandardlibraryaidsCprogrammers.ThelibrarysourcelistingsareavailableelectronicallyviaInternetandvariousothercommunicationservicesaswellasona

companiondiskette.

Assemblylanguageprogrammingistimeconsuming.Softwareengineersestimatethatdevelopersspendonlyaboutthirtypercentoftheirtimecodingasolutiontoaproblem.EvenifittooktwiceasmuchtimetowriteaprograminassemblyversussomeHLL,therewouldonlybeafifteenpercentdifferenceinthetotalprojectcompletiontime.Infact,goodassemblylanguageprogrammersdonotneedtwiceasmuchtimetoimplementsomethinginassemblylanguage.ItistrueusingaHLLwillsavesometime;however,thesavingsisinsufficienttocounterthebenefitsofusingassemblylanguage.

Improvedcompilertechnologyhaseliminatedtheneedforassemblylanguage.Thisisn'ttrueandprobablyneverwillbetrue.Optimizingcompilersaregettingbettereveryday.However,assemblylanguageprogrammersgetbetterperformancebywritingtheircodedifferentlythantheywouldiftheywereusingsomeHLL.IfassemblylanguageprogrammerswrotetheirprogramsinCandthentranslatedthemmanuallyintoassembly,agoodCcompilerwouldproduceequivalent,orevenbetter,code.Thosewhomakethisclaimaboutcompilertechnologyarecomparingtheir

hand-compiledcodeagainstthatproducedbyacompiler.Compilersdoamuchbetterjobofcompilingthanhumans.Thenagain,you'llnevercatchanassemblylanguageprogrammerwriting"CcodewithMOVinstructions."Afterall,that'swhyyouuseCcompilers.

Today,machinesaresofastthatwenolongerneedtouseassembly.Itisamazingthatpeoplewillspendlotsofmoneytobuyamachineslightlyfasterthantheonetheyown,buttheywon'tspendanyextratimewritingtheircodeinassemblysoitrunsfasteronthesamehardware.There

aremanyragingdebatesaboutthespeedofmachinesversusthespeedofthesoftware,butonefactremains:

usersalwayswantmorespeed.Onanygivenmachine,thefastestpossibleprogramswillbewritteninassemblylanguage.

Ifyouneedmorespeed,youshoulduseabetteralgorithmratherthanswitchtoassemblylanguage.Whycan'tyouusethisbetteralgorithminassemblylanguage?

Whatifyou'realreadyusingthebestalgorithmyoucanfindandit'sstilltooslow?

Thisisatotallybogusargument

againstassemblylanguage.AnyalgorithmyoucanimplementinaHLLyoucanimplementinassembly.Ontheotherhand,therearemanyalgorithmsyoucanimplementinassemblywhichyoucannotimplementinaHLL.

Assemblylanguageisnotportable.Thisisanundeniablefact.An80x86assemblylanguageprogramwrittenforanIBMPCwillnotrunonanAppleMacintosh.Indeed,assemblylanguageprogramswrittenfortheAppleMacintoshwillnotrunonanAmiga,eventhoughtheysharethesame680x0microprocessor.Ifyouneedtorunyourprogramondifferentmachines,you'llhavetothinklongandhardaboutusingassemblylanguage.UsingC（orsomeotherHLL）isnoguaranteethatyourprogramwillbeportable.CprogramswrittenfortheIBMPCwon'tcompileandrunonaMacintosh.Andeveniftheydid,mostMacownerswouldn'taccepttheresult.

Portabilityisprobablythebiggestcomplaintpeoplehaveagainstassemblylanguage.Theyrefusetouseassemblybecauseitisnotportable,andthentheyturnaroundandwriteequallynon-portableprogramsinC.

Yes,therearelotsoflies,misconceptions,myths,andhalf-truthsconcerningassemblylanguage.Whateveryoudo,makesureyoulearnassemblylanguagebeforeformingyourownopinions.Speakingoutinignorancemayimpressotherswhoknowlessthanyoudo,butitwon'timpressthosewhoknowthetruth.

2What'sRightWithAssemblyLanguage?

Anoldjokegoessomethinglikethis:

"Therearethreereasonsforusingassemblylanguage:

speed,

speed,andmorespeed."Eventhosewhoabsolutelyhateassemblylanguagewilladmitthatif

speedisyourprimaryconcern,assemblylanguageisthewaytogo.Assemblylanguagehasseveralbenefits:

•

（1）Speed.Assemblylanguageprogramsaregenerallythefastestprogramsaround.

•

（2）Space.Assemblylanguageprogramsareoftenthesmallest.

•（3）Capability.YoucandothingsinassemblywhicharedifficultorimpossibleinHLLs.

•（4）Knowledge.Yourknowledgeofassemblylanguagewillhelpyouwritebetterprograms,evenwhenusingHLLs.

Assemblylanguageistheuncontestedspeedchampionamongprog