Advanced practical Programming - ZIB · (Lisp, ML, Haskell, Erlang, Ocaml) • Object-oriented...

AdvancedpracticalProgrammingforScientists

SS2017

Thorsten KochZuse Institute Berlin

TU Berlin

Plannedtopics

Overview: Imperative,OOP,Functional,sideeffects,threadsafe,DesignbycontractDesign: Informationhiding,Dependencies,Codingstyle,Inputchecking,ErrorHandlingDesign: Overallprogramdesign,Datastructures,MemoryallocationTools: git,gdb,undodb,doxygenLanguagesandcorrectness:Designerrors/problemsC/C++,C89/C99/C11,Compilerswitches,assert,flexelint,FP,HowtowritecorrectprogramsTesting:black-box,white-box,unittests,regressiontests,errortests,speedtestsTools:gcov,jenkins,cmake,doxygen,make,gprof,valgrind,cppcheck,clangSoftwaremetrics:Why,Examples,Isituseful?ControlflowcomplexityParallelprogramming:OpenMP,MPI,pthreads,OpenCLProgramoptimization:Codeoptimization,linkinglibrariesHowtodesignlargeprogramsCode-shootoutandcomparison:Documentation,Releasemanagement

Allinformationissubjecttochange.

AdvancedProgramming 4

Vorlesung12.05:DigitalFuture

Please register yourself viahttps://science-match.tagesspiegel.de/the-digital-future-may-2017Voucher/VIPCode:*future17-1*


Administrativeaffairs

AllemailsrelatedtothislectureshouldstartwithAPPFSinthesubject.

Everybodyparticipatinginthislecture,pleasesendanemailto<[email protected]>withyourNameandMatrikel-Nr.

Wewillsetupamailinglistforannouncementsanddiscussion.Everythingisherehttp://www.zib.de/koch/lectures/ss2017_appfs.php

Ifyouneedthecertificate,regularattendance,completionofhomeworkassignments,andinparticularparticipationinoursmallprogrammingprojectisexpected.GradeswillbebasedontheoutcomeandafewquestionsaboutitJ .

Nogroups.


Exercises(plan)

ExercisespartI:ReadingandwritingData1. 21.04.Readingcsv2. 28.04.Readingxml3. 05.05.Readingbinary4. 05.05.Checkinginputdata

ExercisepartII:Timeseriesprediction5. 26.05.Makingitwork1(make)6. 02.06.Makingitwork2(Documentation,fixinginputdata)7. 09.06.Testing8. 16.06.Measuringperformance,serializingdatastructures9. 23.06.Analyzingcodequality10. 30.06.Linkingthirdpartylibraries(staticvs.shared)11. 07.07.Makingitbetter


Howtosubmitexercises

• Youcansubmittheexercisesinanyprogramminglanguage.

• IthastorunonmyRasberry-pirunningLinux

• Examplesolutionswillbeprovidedatleastinoneofthefollowinglanguages:C99,C++14,python3,Ada2012.

• Ifyouuseanythingelse,youareonyourown.

• Iwilljudgeyourcodenevertheless.


Registeratgithub.comGotohttps://github.com/mattmilten/appfs

ForkChangePullrequest

Createanew folder with your name and then make apullrequest



Attitudes

Algorithmengineeringreferstotheprocessrequiredtotransformapencil-and-paperalgorithmintoarobust,efficient,welltested,andeasilyusableimplementation.

— Bader,Moret,Sanders

RealProgrammersdon'tcommenttheircode.Ifitwashardtowrite,itshouldbehardtounderstandandhardertomodify.

— Fortune(6)

Bewareofbugsintheaboveprogram.Ihaveonlyproveditcorrect,nottriedit.

—D.E.Knuth

Thesinglemostimportantruleoftestingistodo it.— Kernighan,Pike

Laws,Rules,andObjectives

• Laws describethefeasibleregionofasolution• Objectives (aredirections)describingwhichsolutiontoprefer• Rules trytoexclude(ruleout)badsolutions

“Look,that'swhythere'srules,understand?Sothatyouthinkbeforeyoubreak'em.”

―TerryPratchett,ThiefofTime

IngeneralIrecommendtofollowrules,untilyouaresureyouunderstandwhattheruleswantedtoachieveandyoubelieveyourobjectivesareservedbetterbynotobeyingtherule.

Butthinkfirst!

Iftheunionofallrulesdefinesanemptyspace,resistthetemptationtochangetheobjectivetolookforasolutionthatviolatestheleastnumberofrules.Slacksolutionsusuallyhaveahorribleobjectivevalue.


Examples

Thespeedoflightc invacuumisauniversalphysicalconstant.Itsexactvalueis299792458 m/s.Accordingtospecialrelativity,c isthemaximumspeedatwhichallconventionalmatterandhenceallknownformsofinformationintheuniversecantravel.(Wikipedia)

“Everythingshouldbemadeassimpleaspossible,butnosimpler.”― AlbertEinstein

Don’tusegoto!Seehttps://softwareengineering.stackexchange.com/questions/125715/do-we-still-have-a-case-against-the-goto-statement

Adesignerknowshehasachievedperfectionnotwhenthereisnothinglefttoadd,butwhenthereisnothinglefttotakeaway.

―AntoinedeSaint-Exupery


ImperativeProgramming

Incomputerscienceterminology,imperativeprogrammingisaprogrammingparadigmthatdescribescomputationintermsofstatementsthatchangeaprogramstate.Inmuchthesamewaythatimperativemoodinnaturallanguagesexpressescommandstotakeaction,imperativeprogramsdefinesequencesofcommandsforthecomputertoperform.

Imperativeprogramming,http://en.wikipedia.org/w/index.php?title=Imperative_programming&oldid=624302389 (lastvisitedSept.21,2014).

ImperativeProgrammierungisteinProgrammierparadigma.DanachwerdenProgrammesoentwickelt,dass„einProgrammauseinerFolgevonAnweisungenbesteht,dievorgeben,inwelcherReihenfolgewasvomComputergetanwerdensoll“.

DieimperativeProgrammierungistdasamlängstenbekannteProgrammierparadigma.DieseVorgehensweisewar,bedingtdurchdenSprachumfangfrühererProgrammiersprachen,ehemalsdieklassischeArtdesProgrammierens.SieliegtdemEntwurfvonvielenProgrammiersprachen,zumBeispielALGOL,Fortran,Pascal,Ada,PL/I,Cobol,CundallenAssemblersprachenzugrunde.

Seite„ImperativeProgrammierung“.In:Wikipedia,DiefreieEnzyklopädie.Bearbeitungsstand:20.September2014,14:27UTC.URL:http://de.wikipedia.org/w/index.php?title=Imperative_Programmierung&oldid=134202110 (Abgerufen:21.September2014,20:41UTC)


ImperativeProgramming

Iamincommand!

input->putput->outputDataseparatedfrominstructions(moreorlessJ asinstructionsaredata)Von-NeumannArchitecture/Stored-Program-ComputerAccessMemory,docomputationsincl.conditional,PCprogramcounter->allows:goto (jump),if(conditional),while(loop)

1. Doit!2. Anyway!

Structuredprogrammingvs.goto

Blocks,subroutines,scopes.


Object-Oriented Programming

Buildingyourownworldofobjects

Object-orientedprogrammingattemptstoprovideamodelforprogrammingbasedonobjects.OOprogrammingintegratescodeanddatausingtheconceptofan“object”.Anobjectisanabstractdatatypewiththeadditionofpolymorphism andinheritance.

Anobjecthasbothstate(data)andbehavior(code).

->Informationhiding->polymorphismcomesnaturally->singlevs.multipleinheritance.->templatesandgenerics


FunctionalProgramming

Thewaymathematiciansthink.Functionalprogrammingisastyleofbuildingthestructureandelementsofcomputerprograms,thattreatscomputationastheevaluationofmathematicalfunctionsandavoidschangingstateandmutabledata.Infunctionalcode,theoutputvalueofafunctiondependsonlyontheargumentsthatareinputtothefunction,socallingafunctionftwicewiththesamevalueforanargumentxwillproducethesameresultf(x)bothtimes.Eliminatingsideeffects,i.e.changesinstatethatdonotdependonthefunctioninputs,canmakeitmucheasiertounderstandandpredictthebehaviorofaprogram,whichisoneofthekeymotivationsforthedevelopmentoffunctionalprogramming.->sideeffects/mutablestate->rand(),getchar(),putchar()->callbyvalue,callbyreference->threadsafeness->errno


Programming Paradigms

• Imperativeprogramming– definescomputationasstatementsthatchangeaprogramstate(Assembler)

• Proceduralprogramming,structuredprogramming– specifiesthestepstheprogrammusttaketoreachthedesiredstate(C,Pascal,Fortran77)

• Functionalprogramming– treatscomputationastheevaluationofmathematicalfunctionsandavoidsstateandmutabledata(Lisp,ML,Haskell,Erlang,Ocaml)

• Object-orientedprogramming(OOP)– organizesprogramsasobjects:datastructuresconsistingofdatafields andmethodstogetherwiththeirinteractions(Smalltalk,C++,Java,Eiffel)

• Declarativeprogramming– definescomputationlogicwithoutdefiningitscontrolflow(Prolog)

• Event-drivenprogramming– theflowoftheprogramisdeterminedbyevents,suchassensoroutputsoruseractions(mouseclicks,keypresses)ormessagesfromotherprogramsorthreads(JavaScript)


Haveyouever...

• wastedalotoftimecodingthewrongalgorithm?• usedadatastructurethatwasmuchtoocomplicated?• testedaprogrambutmissedanobviousproblem?• spentadaylookingforabugyoushouldhavefoundinfiveminutes?• neededtomakeaprogramrunthreetimesfasteranduselessmemory?• struggledtomoveaprogramfromonearchitecturetoanother?• triedtomakeamodestchangeinsomeoneelse’sprogram?• rewrittenaprogrambecauseyoucouldn’tunderstandit?

Wasitfun?

From:Kernighan,Pike „Thepractise of programming“


Designgoals

Theseinclude

• simplicity,whichkeepsprogramsshortandmanageable;• clarity,whichmakessuretheyareeasytounderstand,forpeople

aswellasmachines;• generality,whichmeanstheyworkwellinabroadrangeof

situationsandadaptwellasnewsituationsarise;and• automation,whichletsthemachinedotheworkforus,freeingus

frommundanetasks.

From:Kernighan,Pike „Thepractise of programming“AdvancedProgramming 22

WinnerOSC1990Bestsmall programm

v,i,j,k,l,s,a[99];

main()

{

for(scanf("%d",&s);*a-s;v=a[j*=v]-a[i],k=i<s,j+=(v=j<s&&(!k&&!!printf(2+"\n\n%c"-(!l<<!j)," #Q"[l^v?(l^j)&1:2])&&++l||a[i]<s&&v&&v-i+j&&v+i-j))&&!(l%=s),v||(i==j?a[i+=k]=0:++a[i])>=s*k&&++a[--i]);

}

What might it possibly do?


Howtoachievethis

• Beabletofollowcontrolflow(-imperative,+structured,-OO,+functional)• Structuringprogramsintounits(-imperative,+structured,+OO)• Minimizedependencies(betweencomponents)

• Minimizescope• Minimizesideeffects(+functional)• Datahiding(+OO)• Howaboutthingshappeningautomatic?

(memberfunctionsinC++,Garbagecollection)• Beingclever?:while(*s++=*t++);• DbC


Somethingto think about

int data[10000]; // all 0..255

long long fun = 0;

unsigned i;

[…]

int t = (data[i] - 128) >> 31;

fun += ~t & data[i];


Thisis notthe way/* The Computer Language Benchmarks Game http://benchmarksgame.alioth.debian.org/

Contributed by Dmitry Vyukov

*/

#define _GNU_SOURCE

#include <stdlib.h>

[…]

#define CL_SIZE 64

void* cache_aligned_malloc(size_t sz)

{

char* mem;

char* res;

void** pos;

mem = (char*)malloc(sz + 2 * CL_SIZE);

if (mem == 0)

exit(1);

res = (char*)((uintptr_t)(mem + CL_SIZE) & ~(CL_SIZE - 1));

pos = (void**)(res - sizeof(void*));

pos[0] = mem;

return res;

}


DesignbyContract

(DbC),isanapproachfordesigningsoftware.Itprescribesthatsoftwaredesignersshoulddefineformal,preciseandverifiableinterfacespecificationsforsoftwarecomponents,whichextendtheordinarydefinitionofabstractdatatypeswithpreconditions,post-conditionsandinvariants.Thesespecificationsarereferredtoas“contracts”,inaccordancewithaconceptualmetaphorwiththeconditionsandobligationsofbusinesscontracts.

Pre-conditionsPost-conditionsInvariants


Exercise 1:Setup

Pleasecheckoutthedataforthisexerciselocatedhere:https://github.com/mattmilten/appfs

Youwillfindaprogramnamedex1_gen usedtogeneratetheinputdata.Runthisprogramasfollows:

./ex1_gen 100000000 >ex1.dat

Thefileex1.dat shouldthencontainroughly100millionlines.Youcancheckby

wc -l ex1.dat

Sizeshouldbearound2GB.Thefirstnumberis123456789.


Exercise1:FileFormat

Eachlineshouldconsistsof• asequence-number,• alocation(1or2),and• afloatingpointvalue>0.

Emptylinesareallowed.Commentlinesstartwitha”#”.Everythingaftera”’#”onalineshouldbeignored.

Readinthedataandcomputethegeometricmeanforeachlocation.Beawarethattheremightbesomeerrorsinthedata.


Exercise 1:Whattodo

Writeaprogramnamedex1 inCoryourfavoritelanguage,which

1. Readsinthedatafromex1.dat

2. ComputetheGeometricMean forbothlocationsOutputshouldlooklike:

File:ex1.datwith100001235linesValidvaluesLoc1:50004598withGeoMean:36.7817ValidvaluesLoc2:49994703withGeoMean:36.7825


Exercise 3:Howtoreport

1. Checkinthesourcecodeintogithub asexplained

2. usetime ex1 ex1.dattogettheruntimesofyourprogram

3. Copytheoutputofyourprogram

Sendtheoutputoftime,andyourex1 withsubjectofAPPFSex1vorname nachnameperemailto<[email protected]>

Deadline:27.04.16Uhr(earlier would be better)


Advanced practical Programming - ZIB · (Lisp, ML, Haskell, Erlang, Ocaml) • Object-oriented...

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