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  • How to simplify my code... 2D NSArray in Objective C...?

    - by Tattat
    self.myArray = [NSArray arrayWithObjects: [NSArray arrayWithObjects: [self d], [self generateMySecretObject],nil], [NSArray arrayWithObjects: [self generateMySecretObject], [self generateMySecretObject],nil],nil]; for (int k=0; k<[self.myArray count]; k++) { for(int s = 0; s<[[self.myArray objectAtIndex:k] count]; s++){ [[[self.myArray objectAtIndex:k] objectAtIndex:s] setAttribute:[self generateSecertAttribute]]; } } As you can see this is a simple 2*2 array, but it takes me lots of code to assign the NSArray in very first place, because I found that the NSArray can't assign the size at very beginning. Also, I want to set attribute one by one. I can't think of if my array change to 10*10. How long it could be. So, I hope you guys can give me some suggestions on shorten the code, and more readable. thz

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  • How to insert zeros between bits in a bitmap?

    - by anatolyg
    I have some performance-heavy code that performs bit manipulations. It can be reduced to the following well-defined problem: Given a 13-bit bitmap, construct a 26-bit bitmap that contains the original bits spaced at even positions. To illustrate: 0000000000000000000abcdefghijklm (input, 32 bits) 0000000a0b0c0d0e0f0g0h0i0j0k0l0m (output, 32 bits) I currently have it implemented in the following way in C: if (input & (1 << 12)) output |= 1 << 24; if (input & (1 << 11)) output |= 1 << 22; if (input & (1 << 10)) output |= 1 << 20; ... My compiler (MS Visual Studio) turned this into the following: test eax,1000h jne 0064F5EC or edx,1000000h ... (repeated 13 times with minor differences in constants) I wonder whether i can make it any faster. I would like to have my code written in C, but switching to assembly language is possible. Can i use some MMX/SSE instructions to process all bits at once? Maybe i can use multiplication? (multiply by 0x11111111 or some other magical constant) Would it be better to use condition-set instruction (SETcc) instead of conditional-jump instruction? If yes, how can i make the compiler produce such code for me? Any other idea how to make it faster? Any idea how to do the inverse bitmap transformation (i have to implement it too, bit it's less critical)?

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  • How efficient is an if statement compared to a test that doesn't use an if? (C++)

    - by Keand64
    I need a program to get the smaller of two numbers, and I'm wondering if using a standard "if x is less than y" int a, b, low; if (a < b) low = a; else low = a; is more or less efficient than this: int a, b, low; low = b + ((a - b) & ((a - b) >> 31)); (or the variation of putting int delta = a - b at the top and rerplacing instances of a - b with that). I'm just wondering which one of these would be more efficient (or if the difference is to miniscule to be relevant), and the efficiency of if-else statements versus alternatives in general.

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  • Why is doing a top(1) on an indexed column in mssql slow?

    - by reinier
    I'm puzzled by the following. I have a DB with around 10 million rows, and (among other indices) on 1 column is an index. Now I have 700k rows where the campaignid is indeed 3835 For all these rows, the connectionid is the same. I just want to find out this connectionid. use messaging_db; SELECT TOP (1) connectionid FROM outgoing_messages WITH (NOLOCK) WHERE (campaignid_int = 3835) Now this query takes approx 30 seconds to perform! I (with my small db knowledge) would expect that it would take any of the rows, and return me that connectionid If I test this same query for a campaign which only has 1 entry, it goes really fast. So the index works. How would I tackle this and why does this not work?

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  • changing the serialization procedure for a graph of objects (.net framework)

    - by pierusch
    Hello I'm developing a scientific application using .net framework. The application depends heavily upon a large data structure (a tree like structure) that has been serialized using a standard binaryformatter object. The graph structure looks like this: <serializable()>Public class BigObjet inherits list(of smallObject) end class <serializable()>public class smallObject inherits list(of otherSmallerObjects) end class ... The binaryFormatter object does a nice job but it's not optimized at all and the entire data structure reaches around 100Mb on my filesystem. Deserialization works too but it's pretty slow (around 30seconds on my quad core). I've found a nice .dll on codeproject (see "optimizing serialization...") so I wrote a modified version of the classes above overriding the default serialization/deserialization procedure reaching very good results. The problem is this: I can't lose the data previosly serialized with the old version and I'd like to be able to use the new serialization/deserialization method. I have some ideas but I'm pretty sure someone will be able to give me a proper and better advice ! use an "helper" graph of objects who takes care of the entire serialization/deserialization procedure reading data from the old format and converting them into the classes I nedd. This could work but the binaryformatter "needs" to know the types being serialized so........ :( modify the "old" graph to include a modified version of serialization procedure...so I'll be able to deserialize old file and save them with the new format......this doesn't sound too good imho. well any help will be higly highly appreciated :)

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  • Optimizing BeautifulSoup (Python) code

    - by user283405
    I have code that uses the BeautifulSoup library for parsing, but it is very slow. The code is written in such a way that threads cannot be used. Can anyone help me with this? I am using BeautifulSoup for parsing and than save into a DB. If I comment out the save statement, it still takes a long time, so there is no problem with the database. def parse(self,text): soup = BeautifulSoup(text) arr = soup.findAll('tbody') for i in range(0,len(arr)-1): data=Data() soup2 = BeautifulSoup(str(arr[i])) arr2 = soup2.findAll('td') c=0 for j in arr2: if str(j).find("<a href=") > 0: data.sourceURL = self.getAttributeValue(str(j),'<a href="') else: if c == 2: data.Hits=j.renderContents() #and few others... c = c+1 data.save() Any suggestions? Note: I already ask this question here but that was closed due to incomplete information.

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  • Python Profiling In Windows, How do you ignore Builtin Functions

    - by Tim McJilton
    I have not been capable of finding this anywhere online. I was looking to find out using a profiler how to better optimize my code, and when sorting by which functions use up the most time cumulatively, things like str(), print, and other similar widely used functions eat up much of the profile. What is the best way to profile a python program to get the user-defined functions only to see what areas of their code they can optimize? I hope that makes sense, any light you can shed on this subject would be very appreciated.

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  • building objects from xml file at runtime and intializing, in one pass?

    - by KaluSingh Gabbar
    I have to parse the XML file and build objects representation based on that, now once I get all these data I create entries in various database for these data objects. I have to do second pass over that for value as in the first pass all I could do is build the assets in various databases. and in second pass I get the values for all the data and put it in the database. I have a feeling that this can be done in a single pass but I just want to see what are your opinions. As I am just a student who started with professional work, experienced ppl please help. Can someone who have ideas or done similar work, please provide some light on the topic so that I can think over the possibility of the work and get the prototype going based on your suggestion. Thanks a lot for your precious time, I honestly appreciate it.

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  • Biggest performance improvement you've had with the smallest change?

    - by JoelFan
    What's the biggest performance improvement you've had with the smallest change? For example, I once improved the performance of a certain page on a high-profile web app by a factor of 10, just by moving "where customerID = ?" to a different place inside a complicated SQL statement (before my change it had been selecting all customers in a join, then later selecting out the desired customer).

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  • Ruby Challenge - efficiently change the last character of every word in a sentence to a capital

    - by emson
    Hi All I recently was challenged to write some Ruby code to change the last character of every word in a sentence into a capital. Such that the string: "script to convert the last letter of every word to a capital" becomes "scripT tO converT thE lasT letteR oF everY worD tO A capitaL" This was my optimal solution however I'm sure you wizards have much better solutions and I would be really interested to hear them. "script to convert the last letter of every word to a capital".split.map{|w|w<<w.slice!(-1).chr.upcase}.join' ' For those interested as to what is going on here is an explanation. split will split the sentence up into an array, the default delimiter is a space and with Ruby you don't need to use brackets here. map the array from split is passed to map which opens a block and process each word (w) in the array. the block slice!(s) off the last character of the word and converts it to a chr (a character not ASCII code) and then capitalises upcase it. This character is now appended << to the word which is missing the sliced last letter. Finally the array of words is now join together with a ' ' to reform the sentence. Enjoy

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  • "variable tracking" is eating my compile time!

    - by wowus
    I have an auto-generated file which looks something like this... static void do_SomeFunc1(void* parameter) { // Do stuff. } // Continues on for another 4000 functions... void dispatch(int id, void* parameter) { switch(id) { case ::SomeClass1::id: return do_SomeFunc1(parameter); case ::SomeClass2::id: return do_SomeFunc2(parameter); // This continues for the next 4000 cases... } } When I build it like this, the build time is enormous. If I inline all the functions automagically into their respective cases using my script, the build time is cut in half. GCC 4.5.0 says ~50% of the build time is being taken up by "variable tracking" when I use -ftime-report. What does this mean and how can I speed compilation while still maintaining the superior cache locality of pulling out the functions from the switch? EDIT: Interestingly enough, the build time has exploded only on debug builds, as per the following profiling information of the whole project (which isn't just the file in question, but still a good metric; the file in question takes the most time to build): Debug: 8 minutes 50 seconds Release: 4 minutes, 25 seconds

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  • Is code clearness killing application performance?

    - by Jorge Córdoba
    As today's code is getting more complex by the minute, code needs to be designed to be maintainable - meaning easy to read, and easy to understand. That being said, I can't help but remember the programs that ran a couple of years ago such as Winamp or some games in which you needed a high performance program because your 486 100 Mhz wouldn't play mp3s with that beautiful mp3 player which consumed all of your CPU cycles. Now I run Media Player (or whatever), start playing an mp3 and it eats up a 25-30% of one of my four cores. Come on!! If a 486 can do it, how can the playback take up so much processor to do the same? I'm a developer myself, and I always used to advise: keep your code simple, don't prematurely optimize for performance. It seems that we've gone from "trying to get it to use the least amount of CPU as possible" to "if it doesn't take too much CPU is all right". So, do you think we are killing performance by ignoring optimizations?

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  • Can I make this two LINQ queries into one query only?

    - by Holli
    From a List of builtAgents I need all items with OptimPriority == 1 and only 5 items with OptimPriority == 0. I do this with two seperate queries but I wonder if I could make this with only one query. IEnumerable<Agent> priorityAgents = from pri in builtAgents where pri.OptimPriority == 1 select pri; IEnumerable<Agent> otherAgents = (from oth in builtAgents where oth.OptimPriority == 0 select oth).Take(5);

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  • What algorithm can I use to determine points within a semi-circle?

    - by khayman218
    I have a list of two-dimensional points and I want to obtain which of them fall within a semi-circle. Originally, the target shape was a rectangle aligned with the x and y axis. So the current algorithm sorts the pairs by their X coord and binary searches to the first one that could fall within the rectangle. Then it iterates over each point sequentially. It stops when it hits one that is beyond both the X and Y upper-bound of the target rectangle. This does not work for a semi-circle as you cannot determine an effective upper/lower x and y bounds for it. The semi-circle can have any orientation. Worst case, I will find the least value of a dimension (say x) in the semi-circle, binary search to the first point which is beyond it and then sequentially test the points until I get beyond the upper bound of that dimension. Basically testing an entire band's worth of points on the grid. The problem being this will end up checking many points which are not within the bounds.

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  • What to do with a big image that's slowing website loading down significantly

    - by Dave
    Hi I'm working on a website that's already been designed by someone else. The designer has used a big image (900x700 100KB) which contains a big logo right across the top, then the background for two columns. This image loads every time a page is loaded as it forms the basis for the website. What should I do with it to improve loading time? I'm considering splitting it up into two or more images, especially the logo on the top. Does splitting up images like that decrease loading time in any significant way? Thanks -edit: Also, all the images are .jpg, would changing this to .gif or .png help anything?

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  • Queries within queries: Is there a better way?

    - by mririgo
    As I build bigger, more advanced web applications, I'm finding myself writing extremely long and complex queries. I tend to write queries within queries a lot because I feel making one call to the database from PHP is better than making several and correlating the data. However, anyone who knows anything about SQL knows about JOINs. Personally, I've used a JOIN or two before, but quickly stopped when I discovered using subqueries because it felt easier and quicker for me to write and maintain. Commonly, I'll do subqueries that may contain one or more subqueries from relative tables. Consider this example: SELECT (SELECT username FROM users WHERE records.user_id = user_id) AS username, (SELECT last_name||', '||first_name FROM users WHERE records.user_id = user_id) AS name, in_timestamp, out_timestamp FROM records ORDER BY in_timestamp Rarely, I'll do subqueries after the WHERE clause. Consider this example: SELECT user_id, (SELECT name FROM organizations WHERE (SELECT organization FROM locations WHERE records.location = location_id) = organization_id) AS organization_name FROM records ORDER BY in_timestamp In these two cases, would I see any sort of improvement if I decided to rewrite the queries using a JOIN? As more of a blanket question, what are the advantages/disadvantages of using subqueries or a JOIN? Is one way more correct or accepted than the other?

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  • Optimize slow ranking query

    - by Juan Pablo Califano
    I need to optimize a query for a ranking that is taking forever (the query itself works, but I know it's awful and I've just tried it with a good number of records and it gives a timeout). I'll briefly explain the model. I have 3 tables: player, team and player_team. I have players, that can belong to a team. Obvious as it sounds, players are stored in the player table and teams in team. In my app, each player can switch teams at any time, and a log has to be mantained. However, a player is considered to belong to only one team at a given time. The current team of a player is the last one he's joined. The structure of player and team is not relevant, I think. I have an id column PK in each. In player_team I have: id (PK) player_id (FK -> player.id) team_id (FK -> team.id) Now, each team is assigned a point for each player that has joined. So, now, I want to get a ranking of the first N teams with the biggest number of players. My first idea was to get first the current players from player_team (that is one record top for each player; this record must be the player's current team). I failed to find a simple way to do it (tried GROUP BY player_team.player_id HAVING player_team.id = MAX(player_team.id), but that didn't cut it. I tried a number of querys that didn't work, but managed to get this working. SELECT COUNT(*) AS total, pt.team_id, p.facebook_uid AS owner_uid, t.color FROM player_team pt JOIN player p ON (p.id = pt.player_id) JOIN team t ON (t.id = pt.team_id) WHERE pt.id IN ( SELECT max(J.id) FROM player_team J GROUP BY J.player_id ) GROUP BY pt.team_id ORDER BY total DESC LIMIT 50 As I said, it works but looks very bad and performs worse, so I'm sure there must be a better way to go. Anyone has any ideas for optimizing this? I'm using mysql, by the way. Thanks in advance Adding the explain. (Sorry, not sure how to format it properly) id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t ALL PRIMARY NULL NULL NULL 5000 Using temporary; Using filesort 1 PRIMARY pt ref FKplayer_pt77082,FKplayer_pt265938,new_index FKplayer_pt77082 4 t.id 30 Using where 1 PRIMARY p eq_ref PRIMARY PRIMARY 4 pt.player_id 1 2 DEPENDENT SUBQUERY J index NULL new_index 8 NULL 150000 Using index

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  • OpenGL Performance Questions

    - by Daniel
    This subject, as with any optimisation problem, gets hit on a lot, but I just couldn't find what I (think) I want. A lot of tutorials, and even SO questions have similar tips; generally covering: Use GL face culling (the OpenGL function, not the scene logic) Only send 1 matrix to the GPU (projectionModelView combination), therefore decreasing the MVP calculations from per vertex to once per model (as it should be). Use interleaved Vertices Minimize as many GL calls as possible, batch where appropriate And possibly a few/many others. I am (for curiosity reasons) rendering 28 million triangles in my application using several vertex buffers. I have tried all the above techniques (to the best of my knowledge), and received almost no performance change. Whilst I am receiving around 40FPS in my implementation, which is by no means problematic, I am still curious as to where these optimisation 'tips' actually come into use? My CPU is idling around 20-50% during rendering, therefore I assume I am GPU bound for increasing performance. Note: I am looking into gDEBugger at the moment Cross posted at Game Development

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  • Building static (but complicated) lookup table using templates.

    - by MarkD
    I am currently in the process of optimizing a numerical analysis code. Within the code, there is a 200x150 element lookup table (currently a static std::vector < std::vector < double ) that is constructed at the beginning of every run. The construction of the lookup table is actually quite complex- the values in the lookup table are constructed using an iterative secant method on a complicated set of equations. Currently, for a simulation, the construction of the lookup table is 20% of the run time (run times are on the order of 25 second, lookup table construction takes 5 seconds). While 5-seconds might not seem to be a lot, when running our MC simulations, where we are running 50k+ simulations, it suddenly becomes a big chunk of time. Along with some other ideas, one thing that has been floated- can we construct this lookup table using templates at compile time? The table itself never changes. Hard-coding a large array isn't a maintainable solution (the equations that go into generating the table are constantly being tweaked), but it seems that if the table can be generated at compile time, it would give us the best of both worlds (easily maintainable, no overhead during runtime). So, I propose the following (much simplified) scenario. Lets say you wanted to generate a static array (use whatever container suits you best- 2D c array, vector of vectors, etc..) at compile time. You have a function defined- double f(int row, int col); where the return value is the entry in the table, row is the lookup table row, and col is the lookup table column. Is it possible to generate this static array at compile time using templates, and how?

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  • improving drawing pythagoras tree

    - by sasquatch90
    Hello. I have written program for drawing pythagoras tree fractal. Can anybody see any way of improving it ? Now it is 120 LOc. I was hoping to shorten it to ~100... import javax.swing.*; import java.util.Scanner; import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import javax.swing.JComponent; public class Main extends JFrame {; public Main(int n) { setSize(900, 900); setTitle("Pythagoras tree"); Draw d = new Draw(n); add(d); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setVisible(true); } private int pow(int n){ int pow = 2; for(int i = 1; i < n; i++){ if(n==0){ pow = 1; } pow = pow*2; } return pow; } public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.print("Give amount of steps: "); int steps = sc.nextInt(); new Main(steps); } } class Draw extends JComponent { private int height; private int width; private int steps; public Draw(int n) { height = 800; width = 800; steps = n; Dimension d = new Dimension(width, height); setMinimumSize(d); setPreferredSize(new Dimension(d)); setMaximumSize(d); } @Override public void paintComponent(Graphics g) { super.paintComponent(g); g.setColor(Color.white); g.fillRect(0, 0, width, height); g.setColor(Color.black); int w = width; int h = height; int x1, x2, x3, x4, x5, y1, y2, y3, y4, y5; int base = w/7; x1 = (w/2)-(base/2); x2 = x1; x3 = (w/2)+(base/2); x4 = x3; x5 = w/2; y1 = (h-(h/15))-base; y2 = h-(h/15); y3 = y2; y4 = y1; y5 = (h-(h/15))-(base+(base/2)); //paint g.drawLine(x1, y1, x2, y2); g.drawLine(x2, y2, x3, y3); g.drawLine(x3, y3, x4, y4); g.drawLine(x1, y1, x4, y4); int n1 = steps; n1--; if(n1>0){ g.drawLine(x1, y1, x5, y5); g.drawLine(x4, y4, x5, y5); paintMore(n1, g, x1, x5, x4, y1, y5, y4); paintMore(n1, g, x4, x5, x1, y4, y5, y1); } } public void paintMore(int n1, Graphics g, double x1_1, double x2_1, double x3_1, double y1_1, double y2_1, double y3_1){ double x1, x2, x3, x4, x5, y1, y2, y3, y4, y5; //counting x1 = x1_1 + (x2_1-x3_1); x2 = x1_1; x3 = x2_1; x4 = x2_1 + (x2_1-x3_1); x5 = ((x2_1 + (x2_1-x3_1)) + ((x2_1-x3_1)/2)) + ((x1_1-x2_1)/2); y1 = y1_1 + (y2_1-y3_1); y2 = y1_1; y3 = y2_1; y4 = y2_1 + (y2_1-y3_1); y5 = ((y1_1 + (y2_1-y3_1)) + ((y2_1-y1_1)/2)) + ((y2_1-y3_1)/2); //paint g.setColor(Color.green); g.drawLine((int)x1, (int)y1, (int)x2, (int)y2); g.drawLine((int)x3, (int)y3, (int)x4, (int)y4); g.drawLine((int)x1, (int)y1, (int)x4, (int)y4); n1--; if(n1>0){ g.drawLine((int)x1, (int)y1, (int)x5, (int)y5); g.drawLine((int)x4, (int)y4, (int)x5, (int)y5); paintMore(n1, g, x1, x5, x4, y1, y5, y4); paintMore(n1, g, x4, x5, x1, y4, y5, y1); } } }

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  • Windows XP GUI programming language

    - by bobir
    I need to write a Windows XP/Vista application, main requirements: Just one .exe file, without extra runtime, like Air, .Net; posstibly a couple of dlls. Very small file size. The application is for network centric usage, similar to ICQ or Gtalk clients. Thanks in advance.

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