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  • Optimizing Code

    - by Claudiu
    You are given a heap of code in your favorite language which combines to form a rather complicated application. It runs rather slowly, and your boss has asked you to optimize it. What are the steps you follow to most efficiently optimize the code? What strategies have you found to be unsuccessful when optimizing code? Re-writes: At what point do you decide to stop optimizing and say "This is as fast as it'll get without a complete re-write." In what cases would you advocate a simple complete re-write anyway? How would you go about designing it?

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  • C++ Program performs better when piped

    - by ET1 Nerd
    I haven't done any programming in a decade. I wanted to get back into it, so I made this little pointless program as practice. The easiest way to describe what it does is with output of my --help codeblock: ./prng_bench --help ./prng_bench: usage: ./prng_bench $N $B [$T] This program will generate an N digit base(B) random number until all N digits are the same. Once a repeating N digit base(B) number is found, the following statistics are displayed: -Decimal value of all N digits. -Time & number of tries taken to randomly find. Optionally, this process is repeated T times. When running multiple repititions, averages for all N digit base(B) numbers are displayed at the end, as well as total time and total tries. My "problem" is that when the problem is "easy", say a 3 digit base 10 number, and I have it do a large number of passes the "total time" is less when piped to grep. ie: command ; command |grep took : ./prng_bench 3 10 999999 ; ./prng_bench 3 10 999999|grep took .... Pass# 999999: All 3 base(10) digits = 3 base(10). Time: 0.00005 secs. Tries: 23 It took 191.86701 secs & 99947208 tries to find 999999 repeating 3 digit base(10) numbers. An average of 0.00019 secs & 99 tries was needed to find each one. It took 159.32355 secs & 99947208 tries to find 999999 repeating 3 digit base(10) numbers. If I run the same command many times w/o grep time is always VERY close. I'm using srand(1234) for now, to test. The code between my calls to clock_gettime() for start and stop do not involve any stream manipulation, which would obviously affect time. I realize this is an exercise in futility, but I'd like to know why it behaves this way. Below is heart of the program. Here's a link to the full source on DB if anybody wants to compile and test. https://www.dropbox.com/s/6olqnnjf3unkm2m/prng_bench.cpp clock_gettime() requires -lrt. for (int pass_num=1; pass_num<=passes; pass_num++) { //Executes $passes # of times. clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &temp_time); //get time start_time = timetodouble(temp_time); //convert time to double, store as start_time for(i=1, tries=0; i!=0; tries++) { //loops until 'comparison for' fully completes. counts reps as 'tries'. <------------ for (i=0; i<Ndigits; i++) //Move forward through array. | results[i]=(rand()%base); //assign random num of base to element (digit). | /*for (i=0; i<Ndigits; i++) //---Debug Lines--------------- | std::cout<<" "<<results[i]; //---a LOT of output.---------- | std::cout << "\n"; //---Comment/decoment to disable/enable.*/ // | for (i=Ndigits-1; i>0 && results[i]==results[0]; i--); //Move through array, != element breaks & i!=0, new digits drawn. -| } //If all are equal i will be 0, nested for condition satisfied. -| clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &temp_time); //get time draw_time = (timetodouble(temp_time) - start_time); //convert time to dbl, subtract start_time, set draw_time to diff. total_time += draw_time; //add time for this pass to total. total_tries += tries; //add tries for this pass to total. /*Formated output for each pass: Pass# ---: All -- base(--) digits = -- base(10) Time: ----.---- secs. Tries: ----- (LINE) */ std::cout<<"Pass# "<<std::setw(width_pass)<<pass_num<<": All "<<Ndigits<<" base("<<base<<") digits = " <<std::setw(width_base)<<results[0]<<" base(10). Time: "<<std::setw(width_time)<<draw_time <<" secs. Tries: "<<tries<<"\n"; } if(passes==1) return 0; //No need for totals and averages of 1 pass. /* It took ----.---- secs & ------ tries to find --- repeating -- digit base(--) numbers. (LINE) An average of ---.---- secs & ---- tries was needed to find each one. (LINE)(LINE) */ std::cout<<"It took "<<total_time<<" secs & "<<total_tries<<" tries to find " <<passes<<" repeating "<<Ndigits<<" digit base("<<base<<") numbers.\n" <<"An average of "<<total_time/passes<<" secs & "<<total_tries/passes <<" tries was needed to find each one. \n\n"; return 0;

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  • XNA 2D/3D Drawing method?

    - by Adir
    What would be a better parctice, writing the drawing method inside the GameObject class or in the Game class? GameObject obj = new GameObject(); obj.Draw(); Or GameObject obj = new GameObject(); DrawGameObject(obj);

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  • How do I update my primary key in MySQL?

    - by Wesley
    Ok, this is probably really simple, but I just can't figure it out. I have a primary key in a table that goes from 1-5,000. I need to manually update that id (for other table update purposes) so that it says 5,000-10,000. Can't I manually update this column? Please help!!! Thank you

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  • Why is my regex so much slower compiled than interpreted ?

    - by miket2e
    I have a large and complex C# regex that runs OK when interpreted, but is a bit slow. I'm trying to speed this up by setting RegexOptions.Compiled, and this seems to take about 30 seconds for the first time and instantly after that. I'm trying to negate this by compiling the regex to an assembly first, so my app can be as fast as possible. My problem is when the compiling delay takes place: Regex myComplexRegex = new Regex(regexText, RegexOptions.Compiled); MatchCollection matches = myComplexRegex.Matches(searchText); foreach (Match match in matches) // <--- when the one-time long delay kicks in { } This is making compiling to an assembly basically useless, as I still get the delay on the first foreach call. What I want is for all the compiling delay to be done in advance when I compile to the assembly, not when the user runs the app. Where am I going wrong ? (The code I'm using to compile to an assembly is similar to http://www.dijksterhuis.org/regular-expressions-advanced/ , if that's relevant ).

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  • MYSQL autoincrement a column or just have an integer, difference?

    - by David19801
    Hi, If I have a column, set as primary index, and set as INT. If I don't set it as auto increment and just insert random integers which are unique into it, does that slow down future queries compared to autincrementing? Does it speed things up if I run OPTIMIZE on a table with its primary and only index as INT? (assuming only 2 columns, and second column is just some INT value) (the main worry is the upper limit on the autoincrement as theres lots of adds and deletes in my table)

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  • Slow loading of UITableView. How know why?

    - by mamcx
    I have a UITableView that show a long list of data. Use sections and follow the sugestion of http://stackoverflow.com/questions/695814/how-solve-slow-scrolling-in-uitableview . The flow is load a main UITableView & push a second selecting a row from there. However, with 3000 items take 11 seconds to show. I suspect first from the load of the records from sqlite (I preload the first 200). So I cut it to only 50. However, no matter if I preload only 1 or 500, the time is the same. The view is made from IB and all is opaque. I run out of ideas in how detect the problem. I run the Instruments tool but not know what to look. Also, when the user select a cell from the previous UITable, no visual feedback is show (ie: the cell not turn selected) for a while so he thinks he not select it and try several times. Is related to this problem. What to do? NOTE: The problem is only in the actual device: iPod Touch 2d generation Using fmdb as sqlite api Doing the caching in viewDidLoad Using NSDictionary for the caching Using a NSAutoreleasePool for the caching part. Only caching the row ID & mac 4 fields necesary to show the cell data UIView made with interface builder, SDK 2.2.1 Instruments say I use 2.5 MB in the device

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  • jQuery async ajax query and returning value problem (scope, closure)

    - by glebovgin
    Hi. Code not working because of async query and variable scope problem. I can't understand how to solve this. Change to $.ajax method with async:false - not an option. I know about closures, but how I can implement it here - don't know. I've seen all topics here about closures in js and jQuery async problems - but still nothing. Help, please. Here is the code: var map = null; var marker; var cluster = null; function refreshMap() { var markers = []; var markerImage = new google.maps.MarkerImage('/images/image-1_32_t.png', new google.maps.Size(32, 32)); $.get('/get_users.php',{},function(data){ if(data.status == 'error') return false; var users = data.users; // here users.length = 1 - this is ok; for(var i in users) { //here I have every values from users - ok var latLng = new google.maps.LatLng(users[i].lat, users[i].lng); var mark = new google.maps.Marker({ position: latLng, icon: markerImage }); markers.push(mark); alert(markers.length); // length 1 } },'json'); alert(markers.length); // length 0 //if I have alert() above - I get result cluster = new MarkerClusterer(map, markers, { maxZoom: null, gridSize: null }); } Thanks.

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  • Concate String In MYSQL

    - by streetparade
    How can i concate this string in mysql desc=desc+$desct what i want is each time i insert a variable from PHP that the string is added to the string which was already in db and seperated with || the field desc should look like this desc 10||30||90||710 say i want to add the value 20 desc 10||30||90||710||20 then the desc field should look like this How can i implement this?

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  • Are conditional subqueries optimized out, if the condition is false?

    - by Tobias Schulte
    I have a table foo and a table bar, where each foo might have a bar (and a bar might belong to multiple foos). Now I need to select all foos with a bar. My sql looks like this SELECT * FROM foo f WHERE [...] AND ($param IS NULL OR (SELECT ((COUNT(*))>0) FROM bar b WHERE f.bar = b.id)) with $param being replaced at runtime. The question is: Will the subquery be executed even if param is null, or will the dbms optimize the subquery out? We are using mysql, mssql and oracle. Is there a difference between these regarding the above?

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  • Javascript Regex: Testing string for intelligent query

    - by Shyam
    Hi, I have a string that holds user input. This string can contain various types of data, like: a six digit id a zipcode that contains out of 4 digits and two alphanumeric characters a name (characters only) As I am using this string to search through a database, the query type is determined on the type of search, which i want to handle serverside using JavaScript (yes, I am using JavaScript serverside). Searching on StackOverflow, brought me some interesting information, like the .test-method, which seems perfect for my needs. The test-method returns either true or false based on the evaluation on the string using a regex object. I am using this page as a reference: http://www.javascriptkit.com/jsref/regexp.shtml So I am trying to determine the zipcode, by using the following very noobish regex. var r = /[A-Za-z]{2,2}/ As far I can understand, this should limit the amount of occurrences of alphanumeric characters to a maximum of two. See beneath the output of my JavaScript console. > var r = /[A-Za-z]{2,2}/ > var x = "2233AL" > r.test(x) true > var x = "2233A" > r.test(x) false > var x = "2233ALL" > r.test(x) true /* i want this to be false */ > A little help would be really appreciated!

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  • How to measure how long is a function running?

    - by rhose87
    I want to see how long a function is running. So I added a timer object on my form and I came out with this code: private int counter = 0; //inside button click I have: timer = new Timer(); timer.Tick += new EventHandler(timer_Tick); timer.Start(); Result result = new Result(); result = new GeneticAlgorithms().TabuSearch(parametersTabu, functia); timer.Stop(); and: private void timer_Tick(object sender, EventArgs e) { counter++; btnTabuSearch.Text = counter.ToString(); } But this is not counting anything. Any ideas?

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  • Maven + Tomcat acceleration

    - by Bar
    I am writing a web application with Maven in the Eclipse IDE, and use Tomcat servlet container. So, I run Maven like this: mvn clean compile. It is reasonable that after this oepration I must re-run Tomcat so it can reinitialize the context (Sysdeo Tomcat launcher helps a lot). The problem is Maven execution and subsequebt Tomcat re-running takes noticable amount of time (like 10+ seconds for Maven and 20+ sec. for Tomcat, because of logging, Hibernate mappings, etc.) every time I do it. Is there any automated and more faster solution for these two operatioins? As I see it, a way better solution can be moving re-compiled classes only to the target dir.

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  • why use the "!!!"?

    - by lazyanno
    as follow codes: var a = {}; if(!!!a[tabType]){ a[tabType] = []; a[tabType].push([self,boxObj]); }else{ a[tabType].push([self,boxObj]); } i think !!!a[tabType] equals !a[tabType] why use the "!!!" not "!" ? thank you!

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  • Execute multiple queries

    - by smartali89
    I am using OleDB for executing my queries in C#, Is there any way I can execute multiple queries in one command statement? I tried to separate them with semi-colon (;) but it gives error "Characters found at the end" I have to execute a few hundreds of queries at once.

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  • 'Good' programming form in maintaining / updating / accessing files by entry

    - by zhermes
    Basic Question: If I'm storying/modifying data, should I access elements of a file by index hard-coded index, i.e. targetFile.getElement(5); via a hardcoded identifier (internally translated into index), i.e. target.getElementWithID("Desired Element"), or with some intermediate DESIRED_ELEMENT = 5; ... target.getElement(DESIRED_ELEMENT), etc. Background: My program (c++) stores data in lots of different 'dataFile's. I also keep a list of all of the data-files in another file---a 'listFile'---which also stores some of each one's properties (see below, but i.e. what it's name is, how many lines of information it has etc.). There is an object which manages the data files and the list file, call it a 'fileKeeper'. The entries of a listFile look something like: filename , contents name , number of lines , some more numbers ... Its definitely possible that I may add / remove fields from this list --- but in general, they'll stay static. Right now, I have a constant string array which holds the identification of each element in each entry, something like: const string fileKeeper::idKeys[] = { "FileName" , "Contents" , "NumLines" ... }; const int fileKeeper::idKeysNum = 6; // 6 - for example I'm trying to manage this stuff in 'good' programatic form. Thus, when I want to retrieve the number of lines in a file (for example), instead of having a method which just retrieves the '3'rd element... Instead I do something like: string desiredID = "NumLines"; int desiredIndex = indexForID(desiredID); string desiredElement = elementForIndex(desiredIndex); where the function indexForID() goes through the entries of idKeys until it finds desiredID then returns the index it corresponds to. And elementForIndex(index) actually goes into the listFile to retrieve the index'th element of the comma-delimited string. Problem: This still seems pretty ugly / poor-form. Is there a way I should be doing this? If not, what are some general ways in which this is usually done? Thanks!

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  • How to optimize this simple function which translates input bits into words?

    - by psihodelia
    I have written a function which reads an input buffer of bytes and produces an output buffer of words where every word can be either 0x0081 for each ON bit of the input buffer or 0x007F for each OFF bit. The length of the input buffer is given. Both arrays have enough physical place. I also have about 2Kbyte free RAM which I can use for lookup tables or so. Now, I found that this function is my bottleneck in a real time application. It will be called very frequently. Can you please suggest a way how to optimize this function? I see one possibility could be to use only one buffer and do in-place substitution. void inline BitsToWords(int8 *pc_BufIn, int16 *pw_BufOut, int32 BufInLen) { int32 i,j,z=0; for(i=0; i<BufInLen; i++) { for(j=0; j<8; j++, z++) { pw_BufOut[z] = ( ((pc_BufIn[i] >> (7-j))&0x01) == 1? 0x0081: 0x007f ); } } } Please do not offer any compiler specific or CPU/Hardware specific optimization, because it is a multi-platform project.

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  • MySQL Query - WHERE and IF?

    - by Prash
    I'm not quite sure how to right this query. Basically, I'm going to have a table with two columns (OS and country_code) - more columns too, but those are the conditional ones. These will be either set to 0 for all, or specific ones, separated by commas. Now, what I'm trying achieve is pull data from the table if the OS and country_code = 0, or if they contain matching data (separated by commas). Then, I have a column for time. I want to select rows where the time is GREATER than the time column, unless the column time_t is set to false, in which case this shouldn't matter. I hope I explained it right? This is what I kind of have so far: $get = $db->prepare("SELECT * FROM commands WHERE country_code = 0 OR country_code LIKE :country_code AND OS = 0 OR OS LIKE :OS AND IF (time_t = 1, expiry > NOW()) "); $get->execute(array( ':country_code' => "%{$data['country_code']}%", ':OS' => "%{$data['OS']}%" ));

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  • SQL Server GROUP BY troubles!

    - by Lucas311
    I'm getting a frustrating error in one of my SQL Server 2008 queries. It parses fine, but crashes when I try to execute. The error I get is the following: Msg 8120, Level 16, State 1, Line 4 Column 'customertraffic_return.company' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause. SELECT * FROM (SELECT ctr.sp_id AS spid, Substring(ctr.company, 1, 20) AS company, cci.email_address AS tech_email, CASE WHEN rating IS NULL THEN 'unknown' ELSE rating END AS rating FROM customer_contactinfo cci INNER JOIN customertraffic_return ctr ON ctr.sp_id = cci.sp_id WHERE cci.email_address <> '' AND cci.email_address NOT LIKE '%hotmail%' AND cci.email_address IS NOT NULL AND ( region LIKE 'Europe%' OR region LIKE 'Asia%' ) AND SERVICE IN ( '1', '2' ) AND ( rating IN ( 'Premiere', 'Standard', 'unknown' ) OR rating IS NULL ) AND msgcount >= 5000 GROUP BY ctr.sp_id, cci.email_address) AS a WHERE spid NOT IN (SELECT spid FROM customer_exclude) GROUP BY spid, tech_email

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  • Best practice for avoiding locks on a heavily read table?

    - by Luiggi
    Hi, I have a big database (~4GB), with 2 large tables (~3M records) having ~180K SELECTs/hour, ~2k UPDATEs/hour and ~1k INSERTs+DELETEs/hour. What would be the best practice to guarantee no locks for the reading tasks while inserting/updating/deleting? I was thinking about using a NOLOCK hint, but there is so much discussed about this (is good, is bad, it depends) that I'm a bit lost. I must say I've tried this in a dev environment and I didn't find any problems, but I don't want to put it on production until I get some feedback... Thank you! Luiggi

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  • Strange profiler behavior: same functions, different performances

    - by arthurprs
    I was learning to use gprof and then i got weird results for this code: int one(int a, int b) { return a / (b + 1); } int two(int a, int b) { return a / (b + 1); } int main() { for (int i = 1; i < 30000000; i++) { two(i, i * 2); one(i, i * 2); } return 0; } and this is the profiler output % cumulative self self total time seconds seconds calls ns/call ns/call name 48.39 0.90 0.90 29999999 30.00 30.00 one(int, int) 40.86 1.66 0.76 29999999 25.33 25.33 two(int, int) 10.75 1.86 0.20 main If i call one then two the result is the inverse, two takes more time than one both are the same functions, but the first calls always take less time then the second Why is that? Note: The assembly code is exactly the same and code is being compiled with no optimizations

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  • Beginner having difficulty with SQL query

    - by Vulcanizer
    Hi, I've been studying SQL for 2 weeks now and I'm preparing for an SQL test. Anyway I'm trying to do this question: For the table: 1 create table data { 2 id int, 3 n1 int not null, 4 n2 int not null, 5 n3 int not null, 6 n4 int not null, 7 primary key (id) 8 } I need to return the relation with tuples (n1, n2, n3) where all the corresponding values for n4 are 0. The problem asks me to solve it WITHOUT using subqueries(nested selects/views) It also gives me an example table and the expected output from my query: 01 insert into data (id, n1, n2, n3, n4) 02 values (1, 2,4,7,0), 03 (2, 2,4,7,0), 04 (3, 3,6,9,8), 05 (4, 1,1,2,1), 06 (5, 1,1,2,0), 07 (6, 1,1,2,0), 08 (7, 5,3,8,0), 09 (8, 5,3,8,0), 10 (9, 5,3,8,0); expects (2,4,7) (5,3,8) and not (1,1,2) since that has a 1 in n4 in one of the cases. The best I could come up with was: 1 SELECT DISTINCT n1, n2, n3 2 FROM data a, data b 3 WHERE a.ID <> b.ID 4 AND a.n1 = b.n1 5 AND a.n2 = b.n2 6 AND a.n3 = b.n3 7 AND a.n4 = b.n4 8 AND a.n4 = 0 but I found out that also prints (1,1,2) since in the example (1,1,2,0) happens twice from IDs 5 and 6. Any suggestions would be really appreciated.

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