C语言英文课件Chapter11.ppt

Chapter11BitOperation Inordertosavememoryspace severalstatussignsareusuallyputtogetherintoonebyte orbit Clanguageisdesignedforstudyingsystemsoftware soitoffersbitoperationwhichseparatestatussignfromsignbytememory Bitoperationisthatwedoitinbinary 11 1numberexpressedincomputer11 2bitoperation11 3bitsegment 11 1NumberExpressedinComputer 1 BitandByteMemoryincomputersystemisconstitutedofmanynamedbyteunits Onebyteismadeupofeightbits andthevalueis0or1ofeverybit Thebitintherightsideiscalled thelowestbit anditsnumberis0 Thebitintheleftsideiscalled thehighestbit andsetthenumbertoeachbitfromthelowesttohighestinorder Diagram11 1isthenumberofeachbitinonebyte Fig11 1Thenumberofeachbitinonebyte2 DigitExpressedbyInitialCodeDigitexpressedbyinitialcodeisthatusingthehighestbitasasignbit 0referstopositivenumber 1referstonegativenumber theotherbitsrepresenttothemselves absolutevalue expressedinbinary Inordertosimpledescription weuseonebytetoexpressoneintegralinthisclass Forexample theinitialcodeof 9is00001001 signbit0referstopositivenumbertheinitialcodeof 9is10001001 signbit0referstonegativenumber3 DigitExpressedbyOppositeCodedigitexpressedbyoppositecodeincludestwocircumstances 1 oppositecodeofpositivenumber thesameastheinitialcode Forexample theoppositecodeof 9is00001001 2 oppositecodeofnegativenumber signbitis1 otherbitsisoppositetotheirabsolutevalue 1turnsto0 0turnsto1 Forexample theoppositecodeof 9is becauseitisanegativenumber signbitis1 othersevenbitsistheoppositeofitsabsolutevaluethattheinitialof 9 sotheoppositeof 9is11110110 4 DigitExpressedbyComplementCodeDigitexpressedbycomplementcodealsoincludestwocircumstances 1 thecomplementcodeofpositivenumber thesameastheinitialcode Forexample thecomplementcodeof 9is0001001 2 thecomplementofnegativenumber signbitis1 otherbitsisoppositetotheirabsolutevalue sinitialcode thenadd1 Forexample thecomplementcodeof 9is becauseitisanegativenumber signbitis1 othersevenbitsistheoppositeofitsabsolutevaluethattheinitialof 9 sotheoppositecodeof 9is11110110 Thenitadds1 Sothecomplementof 9is11110111 Ifweknowthecomplementcodeofanumber therearetwocircumstancesabouttheinitialcode 1 ifthecomplementcode ssignbitis 0 itisapositivenumber socomplementcodeisjustitsinitialcode 2 ifthecomplementcode ssignbitis 1 itisanegativenumber sotheoperationofobservinganinitialcodecanbe signbitisnotchanged otherbitsisoppositetotheirabsolutevalue sinitialcode Thenitadds1 Forexample itisgivenacomplementcodethatis11111001 soitsinitialcodeis10000111 7 becauseitssignbitis 1 itisanegativenumber thesignbitneedn tchanged itisstill 1 othersevenbitsistheoppositeof1111001 soitis0000110now thenitadds1 Itis10000111 5 NumberExpressedinComputer ComplementCodeIncomputesystem digitsareallexpressincomplementcode thereasonisthat wecandowithsignbitandotherbitstogether Alsominuscanbedoneasplusdone Besides whentwonumberswhichareexpressedincomplementcodedoplusoperation ifthereisaentertothehighestbit theenterbitisabandoned 11 2BitOperation 11 2 1BitOperationandItsOperationSigns1 Andeachbitinorder 1 formate x y 2 rule onlywhencorrespondbitis1 itisa Otherwiseitis0 Forexample 3 9 1 0011 1001 0001 1 3 mainusage take orsave somebitofanumber otherbitsare0 2 Oreachbitinorder 1 formate x y 2 rule onlywhencorrespondbitis0 itis0 Otherwiseitis1 Forexample 3 9 11 0011 1001 1011 11 3 mainusage setsomebitto1ofanumber otherbitsisnotchanged 3 XOReachbit 1 formate x y 2 rule whencorrespondbitisthesame itis0 whenitisdifferent itis1 3 9 10 3 Mainusage makesomebittoconvert ifitis1 itwillbeturnedto0 ifitis0 itwillbeturnedto1 otherbitsareallnotchanged 4 Converteachbit 1 formate x 2 rule converteachbitisthatifitis1 itwillbeturnedto0 elseitwillbeturnedto1 inIBM PCcompute 0 0 xffff 9 0 xfff6 3 Mainusage makeanumberindirectly soitstrengthstransplantofprograms 5 Movelefteachbit 1 formate x anumber 2 rule makeeachbitmoveleft thelowestbitsetto0 thehighestbitisoverflow 5 2 20 6 Moverighteachbit 1 formate x anumber 2 rule makeeachbitmoveright thelowestbitwhichismovedoutwillbeabandoned thehighestbit 1 Tounsignednumbersandsignedpositivenumbers itwillbeset0 2 Ifitisasignednegativenumber itisdecidedbythesystemwhichyouareusing set0iscalled logicleftmovement set1iscalled arithmeticrightmovement Forexample 20 2 5 instructions 1 x yand bitnumber andsoon areallintorchar Exceptforconvertingeachbitissingleoperationsign othersaretwooperationsign 2 whenitisdoneintheoperation theoperatorsxandyareallmustfirstconvertedtobinary thenexecutetheoperation Forexample 5 2 5 10100 00101 3 wayofmakinguseof operation1 makeupaninteger thisnumberwillbesetto1whereyouwanttotake orsave orsetto1 otherbitsareallsetto0 2 doandeachbitororeachbitorXOReachbitoperation 4 wayofmakinguseofconvertingeachbitoperation1 do 0 indirectlymakeanumberwhereeachbitis1 2 accordingtowhatyouneed domovingleftormovingrightoperationtomakeanumberwhatyouwish Forexample directlymakeanumberwhereeachbitis1 InIBM PCcomputeitis0 xffff twobytes butinVAX 11 780 itis0 xffffffff fourbytes Ifweuse 0tomakeanumber systemcansuititauto Thedetailoftheapplication pleasereferto example11 1 11 2 2Example 11 1 Inputanintegertovariablenum outputaHexnumbermakedupby8 11bits generalprogress 1 movevariablenumrightbyeightbits andmovethebitswhereitisfrom8to11tothelowfourbits 2 makeupanintegralwheretherelowfourbitsareall1 otherbitsareall0 3 dotheoperationandtonum filenameoftheexamplecode AL11 1 C functionoftheprogram outputanintegralwhichismadeupoffromeightbitstoelevenbits main intnum mask printf Inputaintegernumber scanf d Theresultoftheprogram Inputaintegernumber 1000 result 0 x3Instructionstotheprogram 0 4 Converteachbitabout0 thenitsbitisall1 aftermovingleftbyfourbits itslowfourbitsareall0 otherbitsareall1 thenXOReachbit thelowfourbitsareall1 otherbitsareall0 Thisintegeriswhatwewant example11 2 inputanintegerfromkeyboardandisgiventovariablenum thenoutputitbybit filenameoftheexamplecode AL11 2 C functionoftheprogram outputanintegerbybit include stdio h main intnum mask i printf Inputaintegernumber scanf d Theresultoftheprogram Inputaintegernumber 1000 1000 0000 0011 1110 1000B11 2 3instruction1 ComplexendowoperationExceptforconvertingeachbit otherfivebitoperationscanbeusedwithendowtomakeupofacomplexendowoperation 2 theoperationtothedataswithdifferentlengths alignaccordingthelowbit thehighestbitofshortdataissetaccordingtothehighestbit 1 totheunsignednumberandsignedpositivenumber isset0 2 toasignednegativenumber isset1 11 3bitsegmentintroduction Sometimeswhenwesaveaninformationdon tneedabyte onlyneeda orseveral bits Ifwestillusethisstructuretype itwillwastespaceofmemory Inordertoresolvethisproblem Clanguageimportsabitsegmenttype 1 theconceptanddefinitionofbitsegmentBitsegmentstructuretypeisaspecialstructuretype Itsmembersareallexpressedinbinaryabouttheirlength anditsmembersarecalledsegments Forexample thestatusregisterofCPUisdefinedbysegmenttypeasfollowing structstatus unsignedsign 1 signmark unsignedzero 1 zeromark unsignedcarry 1 carryingbitmark unsignedparity 1 oddoreven overflowmark unsignedhalf carry 1 halfcarryingbitmark unsignednegative 1 minusmark flags Obviously itoccupiesfivebitslessthanitisinastructuretype needssixbits forthestatusregisterofCPUwhichisinbitsegmenttype onlyneedsonebyte 2 instrutions 1 Forbitsegmenttypeisastructuretype thedefinitionofbitsegmenttypeandbitsegmentvariableisthesameasthatofstructuretypeandstructurevariable 2 Whenyouendowavaluetobitsegment youshouldbecarefulaboutthescopeofitsvalue 0 2n 1 3