Search Results

Search found 7671 results on 307 pages for 'slow browsing'.

Page 268/307 | < Previous Page | 264 265 266 267 268 269 270 271 272 273 274 275  | Next Page >

• 1k of Program Space, 64 bytes of RAM. Is assembly an absolute must?

  - by Earlz

  (If your lazy see bottom for TL;DR) Hello, I am planning to build a new (prototype) project dealing with physical computing. Basically, I have wires. These wires all need to have their voltage read at the same time. More than a few hundred microseconds difference between the readings of each wire will completely screw it up. The Arduino takes about 114 microseconds. So the most I could read is 2 or 3 wires before the latency would skew the accuracy of the readings. So my plan is to have an Arduino as the "master" of an array of ATTinys. The arduino is pretty cramped for space, but it's a massive playground compared to the tinys. An ATTiny13A has 1k of flash ROM(program space), 64 bytes of RAM, and 64 bytes of (not-durable and slow) EEPROM. (I'm choosing this for price as well as size) The ATTinys in my system will not do much. Basically, all they will do is wait for a signal from the Master, and then read the voltage of 1 or 2 wires and store it in RAM(or possibly EEPROM if it's that cramped). And then send it to the Master using only 1 wire for data.(no room for more than that!). So far then, all I should have to do is implement trivial voltage reading code (using built in ADC). But this communication bit I'm worried about. Do you think a communication protocol(using just 1 wire!) could even be implemented in such constraints? TL;DR: In less than 1k of program space and 64 bytes of RAM(and 64 bytes of EEPROM) do you think it is possible to implement a 1 wire communication protocol? Would I need to drop to assembly to make it fit? I know that currently my Arduino programs linking to the Wiring library are over 8k, so I'm a bit concerned.

  Read the article

• Is there a fast alternative to creating a Texture2D from a Bitmap object in XNA?

  - by Matthew Bowen

  I've looked around a lot and the only methods I've found for creating a Texture2D from a Bitmap are: using (MemoryStream s = new MemoryStream()) { bmp.Save(s, System.Drawing.Imaging.ImageFormat.Png); s.Seek(0, SeekOrigin.Begin); Texture2D tx = Texture2D.FromFile(device, s); } and Texture2D tx = new Texture2D(device, bmp.Width, bmp.Height, 0, TextureUsage.None, SurfaceFormat.Color); tx.SetData<byte>(rgbValues, 0, rgbValues.Length, SetDataOptions.NoOverwrite); Where rgbValues is a byte array containing the bitmap's pixel data in 32-bit ARGB format. My question is, are there any faster approaches that I can try? I am writing a map editor which has to read in custom-format images (map tiles) and convert them into Texture2D textures to display. The previous version of the editor, which was a C++ implementation, converted the images first into bitmaps and then into textures to be drawn using DirectX. I have attempted the same approach here, however both of the above approaches are significantly too slow. To load into memory all of the textures required for a map takes for the first approach ~250 seconds and for the second approach ~110 seconds on a reasonable spec computer. If there is a method to edit the data of a texture directly (such as with the Bitmap class's LockBits method) then I would be able to convert the custom-format images straight into a Texture2D and hopefully save processing time. Any help would be very much appreciated. Thanks

  Read the article

• Delete Duplicate records from large csv file C# .Net

  - by Sandhurst

  I have created a solution which read a large csv file currently 20-30 mb in size, I have tried to delete the duplicate rows based on certain column values that the user chooses at run time using the usual technique of finding duplicate rows but its so slow that it seems the program is not working at all. What other technique can be applied to remove duplicate records from a csv file Here's the code, definitely I am doing something wrong DataTable dtCSV = ReadCsv(file, columns); //columns is a list of string List column DataTable dt=RemoveDuplicateRecords(dtCSV, columns); private DataTable RemoveDuplicateRecords(DataTable dtCSV, List<string> columns) { DataView dv = dtCSV.DefaultView; string RowFilter=string.Empty; if(dt==null) dt = dv.ToTable().Clone(); DataRow row = dtCSV.Rows[0]; foreach (DataRow row in dtCSV.Rows) { try { RowFilter = string.Empty; foreach (string column in columns) { string col = column; RowFilter += "[" + col + "]" + "='" + row[col].ToString().Replace("'","''") + "' and "; } RowFilter = RowFilter.Substring(0, RowFilter.Length - 4); dv.RowFilter = RowFilter; DataRow dr = dt.NewRow(); bool result = RowExists(dt, RowFilter); if (!result) { dr.ItemArray = dv.ToTable().Rows[0].ItemArray; dt.Rows.Add(dr); } } catch (Exception ex) { } } return dt; }

  Read the article

• jQuery ajax not preloading images

  - by George Wiscombe

  I have a list of galleries, when you click on the title of a gallery it pulls in the contents (HTML with images). When the content is pulled in it preloads the html but not the images, any ideas? This is the JavaScript i'm using: $('#ajax-load').ajaxStart(function() { $(this).show(); }).ajaxStop(function() { $(this).hide();}); // PORTFOLIO SECTION // Hide project details on load $('.project > .details').hide(); // Slide details up / down on click $('.ajax > .header').click(function () { if ($(this).siblings(".details").is(":hidden")) { var detailUrl = $(this).find("a").attr("href"); var $details = $(this).siblings(".details"); $.ajax({ url: detailUrl, data: "", type: "GET", success: function(data) { $details.empty(); $details.html(data); $details.find("ul.project-nav").tabs($details.find(".pane"), {effect: 'fade'}); $details.slideDown("slow"); }}); } else {$(this).siblings(".details").slideUp();} return false; }); You can see this demonstrated at http://www.georgewiscombe.com Thanks in advance!

  Read the article

• Project Euler problem 214, How can i make it more efficient?

  - by Once

  I am becoming more and more addicted to the Project Euler problems. However since one week I am stuck with the #214. Here is a short version of the problem: PHI() is Euler's totient function, i.e. for any given integer n, PHI(n)=numbers of k<=n for which gcd(k,n)=1. We can iterate PHI() to create a chain. For example starting from 18: PHI(18)=6 = PHI(6)=2 = PHI(2)=1. So starting from 18 we get a chain of length 4 (18,6,2,1) The problem is to calculate the sum of all primes less than 40e6 which generate a chain of length 25. I built a function that calculates the chain length of any number and I tested it for small values: it works well and fast. sum of all primes<=20 which generate a chain of length 4: 12 sum of all primes<=1000 which generate a chain of length 10: 39383 Unfortunately my algorithm doesn't scale well. When I apply it to the problem, it takes several hours to calculate... so I stop it because the Project Euler problems must be solved in less than one minute. I thought that my prime detection function might be slow so I fed the program with a list of primes <40e6 to avoid the primality test... The code runs now a little bit faster, but there is still no way to get a solution in less than a few hours (and I don't want this). So is there any "magic trick" that I am missing here ? I really don't understand how to be more efficient on this one... I am not asking for the solution, because fighting with optimization is all the fun of Project Euler. However, any small hint that could put me on the right track would be welcome. Thanks !

  Read the article

• Mysql InnoDB performance optimization and indexing

  - by Davide C

  Hello everybody, I have 2 databases and I need to link information between two big tables (more than 3M entries each, continuously growing). The 1st database has a table 'pages' that stores various information about web pages, and includes the URL of each one. The column 'URL' is a varchar(512) and has no index. The 2nd database has a table 'urlHops' defined as: CREATE TABLE urlHops ( dest varchar(512) NOT NULL, src varchar(512) DEFAULT NULL, timestamp timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, KEY dest_key (dest), KEY src_key (src) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 Now, I need basically to issue (efficiently) queries like this: select p.id,p.URL from db1.pages p, db2.urlHops u where u.src=p.URL and u.dest=? At first, I thought to add an index on pages(URL). But it's a very long column, and I already issue a lot of INSERTs and UPDATEs on the same table (way more than the number of SELECTs I would do using this index). Other possible solutions I thought are: -adding a column to pages, storing the md5 hash of the URL and indexing it; this way I could do queries using the md5 of the URL, with the advantage of an index on a smaller column. -adding another table that contains only page id and page URL, indexing both columns. But this is maybe a waste of space, having only the advantage of not slowing down the inserts and updates I execute on 'pages'. I don't want to slow down the inserts and updates, but at the same time I would be able to do the queries on the URL efficiently. Any advice? My primary concern is performance; if needed, wasting some disk space is not a problem. Thank you, regards Davide

  Read the article

• Porting WebGL game to iPhone's native OpenGL?

  - by ArtPulse

  We are developing a web game that uses WebGL for the two biggest parts of it. Working with HTML / CSS was too slow and too limited, so it's off the table. Thing is, iOS does not support WebGL publicly just yet, only on iAd. It is my guess Apple will eventually support it once the security issues they and Microsoft claim it has are fixed, and looks stable enough. Problem is, if Apple does not do this by the release of the next mayor iOS version, then we will have in our hands a mobile WebGL game that does not run. 6 months of development and testing to waste. So, questions: If that was the case, how viable (regarding amount of time) is it porting the WebGL part of the game to native iPhone OpenGL? I'm afraid that porting will take longer than the development of the game itself. I saw posts on Stack Overflow (like this) that suggested, on Android, adding the OpenGL interface manually to a WebKit element. It'd be slower than native. But either way... Is this something that could be accepted in the AppStore? Apple is very restrictive with these kind of stuff... Thank you all for your time!

  Read the article

• jQuery ajax delete script not actually deleting.

  - by werm

  I have a little personal webapp that I'm working on. I have a link that, when clicked, is supposed to make an ajax call to a php that is supposed to delete that info from a database. For some unknown reason, it won't actually delete the row from the database. I've tried everything I know, but still nothing. I'm sure it's something incredibly easy... Here are the scripts involved. Database output: $sql = "SELECT * FROM bookmark_app"; foreach ($dbh->query($sql) as $row) { echo '<div class="box" id="',$row['id'],'"><img src="images/avatar.jpg" width="75" height="75" border="0" class="avatar"/> <div class="text"><a href="',$row['url'],'">',$row['title'],'</a><br/> </div> /*** Click to delete ***/ <a href="?delete=',$row['id'],'" class="delete">x</a></div> <div class="clear"></div>'; } $dbh = null; Ajax script: $(document).ready(function() { $("a.delete").click(function(){ var element = $(this); var noteid = element.attr("id"); var info = 'id=' + noteid; $.ajax({ type: "GET", url: "includes/delete.php", data: info, success: function(){ element.parent().eq(0).fadeOut("slow"); } }); return false; }); }); Delete code: include('connect.php'); //delete.php?id=IdOfPost if($_GET['id']){ $id = $_GET['id']; //Delete the record of the post $delete = mysql_query("DELETE FROM `db` WHERE `id` = '$id'"); //Redirect the user header("Location:xxxx.php"); }

  Read the article

• Can I perform a search on mail server in Java?

  - by twofivesevenzero

  I am trying to perform a search of my gmail using Java. With JavaMail I can do a message by message search like so: Properties props = System.getProperties(); props.setProperty("mail.store.protocol", "imaps"); Session session = Session.getDefaultInstance(props, null); Store store = session.getStore("imaps"); store.connect("imap.gmail.com", "myUsername", "myPassword"); Folder inbox = store.getFolder("Inbox"); inbox.open(Folder.READ_ONLY); SearchTerm term = new SearchTerm() { @Override public boolean match(Message mess) { try { return mess.getContent().toString().toLowerCase().indexOf("boston") != -1; } catch (IOException ex) { Logger.getLogger(JavaMailTest.class.getName()).log(Level.SEVERE, null, ex); } catch (MessagingException ex) { Logger.getLogger(JavaMailTest.class.getName()).log(Level.SEVERE, null, ex); } return false; } }; Message[] searchResults = inbox.search(term); for(Message m:searchResults) System.out.println("MATCHED: " + m.getFrom()[0]); But this requires downloading each message. Of course I can cache all the results, but this becomes a storage concern with large gmail boxes and also would be very slow (I can only imagine how long it would take to search through gigabytes of text...). So my question is, is there a way of searching through mail on the server, a la gmail's search field? Maybe through Microsoft Exchange? Hours of Googling has turned up nothing.

  Read the article

• Multi-dimensional array edge/border conditions

  - by kirbuchi

  Hi, I'm iterating over a 3 dimensional array (which is an image with 3 values for each pixel) to apply a 3x3 filter to each pixel as follows: //For each value on the image for (i=0;i<3*width*height;i++){ //For each filter value for (j=0;j<9;j++){ if (notOutsideEdgesCondition){ *(**(outArray)+i)+= *(**(pixelArray)+i-1+(j%3)) * (*(filter+j)); } } } I'm using pointer arithmetic because if I used array notation I'd have 4 loops and I'm trying to have the least possible number of loops. My problem is my notOutsideEdgesCondition is getting quite out of hands because I have to consider 8 border cases. I have the following handled conditions Left Column: ((i%width)==0) && (j%3==0) Right Column: ((i-1)%width ==0) && (i>1) && (j%3==2) Upper Row: (i<width) && (j<2) Lower Row: (i>(width*height-width)) && (j>5) and still have to consider the 4 corner cases which will have longer expressions. At this point I've stopped and asked myself if this is the best way to go because If I have a 5 line long conditional evaluation it'll not only be truly painful to debug but will slow the inner loop. That's why I come to you to ask if there's a known algorithm to handle this cases or if there's a better approach for my problem. Thanks a lot.

  Read the article

• use proxy in python to fetch a webpage

  - by carmao

  I am trying to write a function in Python to use a public anonymous proxy and fetch a webpage, but I got a rather strange error. The code (I have Python 2.4): import urllib2 def get_source_html_proxy(url, pip, timeout): # timeout in seconds (maximum number of seconds willing for the code to wait in # case there is a proxy that is not working, then it gives up) proxy_handler = urllib2.ProxyHandler({'http': pip}) opener = urllib2.build_opener(proxy_handler) opener.addheaders = [('User-agent', 'Mozilla/5.0')] urllib2.install_opener(opener) req=urllib2.Request(url) sock=urllib2.urlopen(req) timp=0 # a counter that is going to measure the time until the result (webpage) is # returned while 1: data = sock.read(1024) timp=timp+1 if len(data) < 1024: break timpLimita=50000000 * timeout if timp==timpLimita: # 5 millions is about 1 second break if timp==timpLimita: print IPul + ": Connection is working, but the webpage is fetched in more than 50 seconds. This proxy returns the following IP: " + str(data) return str(data) else: print "This proxy " + IPul + "= good proxy. " + "It returns the following IP: " + str(data) return str(data) # Now, I call the function to test it for one single proxy (IP:port) that does not support user and password (a public high anonymity proxy) #(I put a proxy that I know is working - slow, but is working) rez=get_source_html_proxy("http://www.whatismyip.com/automation/n09230945.asp", "93.84.221.248:3128", 50) print rez The error: Traceback (most recent call last): File "./public_html/cgi-bin/teste5.py", line 43, in ? rez=get_source_html_proxy("http://www.whatismyip.com/automation/n09230945.asp", "93.84.221.248:3128", 50) File "./public_html/cgi-bin/teste5.py", line 18, in get_source_html_proxy sock=urllib2.urlopen(req) File "/usr/lib64/python2.4/urllib2.py", line 130, in urlopen return _opener.open(url, data) File "/usr/lib64/python2.4/urllib2.py", line 358, in open response = self._open(req, data) File "/usr/lib64/python2.4/urllib2.py", line 376, in _open '_open', req) File "/usr/lib64/python2.4/urllib2.py", line 337, in _call_chain result = func(*args) File "/usr/lib64/python2.4/urllib2.py", line 573, in lambda r, proxy=url, type=type, meth=self.proxy_open: \ File "/usr/lib64/python2.4/urllib2.py", line 580, in proxy_open if '@' in host: TypeError: iterable argument required I do not know why the character "@" is an issue (I have no such in my code. Should I have?) Thanks in advance for your valuable help.

  Read the article

• Any high-level languages that can use c libraries?

  - by Isaiah

  I know this question could be in vain, but it's just out of curiosity, and I'm still much a newb^^ Anyways I've been loving python for some time while learning it. My problem is obviously speed issues. I'd like to get into indie game creation, and for the short future, 2d and pygame will work. But I'd eventually like to branch into the 3d area, and python is really too slow to make anything 3d and professional. So I'm wondering if there has ever been work to create a high-level language able to import and use c libraries? I've looked at Genie and it seems to be able to use certain libraries, but I'm not sure to what extent. Will I be able to use it for openGL programing, or in a c game engine? I do know some lisp and enjoy it a lot, but there aren't a great many libraries out there for it. Which leads to the problem: I can't stand C syntax, but C has libraries galore that I could need! And game engines like irrlicht. Is there any language that can be used in place of C around C? Thanks so much guys

  Read the article

• Poor DB4O performance - What am I doing wrong?

  - by Jon

  I read Rob Conery's post about Object databases and thought I'd give it a go. I have a class lets say Book with 15 properties mostly string, some int, one Datetime and 2 decimals. I used Rob's code to open the database file etc to test on a Winforms project not a Web project. So I did the following: for(int i = 0; i < 1000000; i++) { var Book = new Book(); //Assign variables s.Save(Book); } s.CommitChanges(); This took at least a couple of minutes. I then tried to retrieve all data to test speed: var spp = s.All<Passports>(); This one line was quick, however, then doing: sppp.Count() as well as a seperate test doing a foreach loop and incrementing a counter took a couple of minutes. This seems quite slow to me. Am I doing something wrong or am I expecting too much?

  Read the article

• How can I improve this search usability?

  - by Craig Whitley

  This is the first real programming attempt of mine, and theres some major flaws. It's a learning project, and I'm currently re-writing the entire thing as my php is is really messy. I really want to get an idea on how I can improve the actual usability and accesibility of the site at the same time though - so I know how to implement it correctly. The website is basically a comparison website for gameserver hosting. As I mentioned, its a learning project and I don't actually expect any revenue from it. At the moment theres only test data in it, so in the game input box select either 'Battlefied Bad Company 2' or 'Call of Duty 4: Modern Warfare' and ignore the actual search results. http://www.laglessfrag.com I wasn't really sure how to work the search functionality. Basically when you click a game in the drop down box, it sends an ajax request and finds all the locations available to that specific game in the database. After selecting the country theres another ajax to find all the citys available to the game in that country - which gives me the two unique identifiers I need to create the search results. One major and fundamental flaw is that without javascript enabled, the site ceases to function. I'll overcome that in the next re-write, but without the ajax functionality stopping the user 'going wrong' - how can I implement a search that requires two fields without creating extra steps in new pages after form submissions? I'm also no designer so my whole layout and css is a bit rubbish, but this was mainly a learning project as I'm interested in applications / programming rather than design. It's also slow as its on shared hosting, but if I can get it to work correctly then I'm not impartial to chucking a bit of money at it for faster hosting and maybe a bit of advertising and seeing where it goes (if anywhere!). Any info appreciated.

  Read the article

• call addsubview again causes slowdown

  - by Tom

  hi guys, i am writing a little music-game for the iphone. I am almost done, this is the only issue which keeps me from rolling it out. any help to solve this is much appreciated. this is what i do: at my appDelegate I add my menu-view-screen to the window. the menu-view-screen acts as a container and controls which view gets presented to the user. means, on the menu-view-screen I got 4 buttons (new game, options, faq, highscore). when the user clicks on a button something as this happens: if (self.gameViewController == nil) { GameViewController *viewController = [[GameViewController alloc] initWithNibName:@"GameViewController" bundle:nil]; self.gameViewController = viewController; [viewController release]; } [self.view addSubview:self.gameViewController.view]; [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleSwitchViewNotificationFromGameView:) name:@"SwitchView" object:gameViewController]; when the user returns to the menu, this piece of code gets executed: [[NSNotificationCenter defaultCenter] removeObserver:self]; [self.gameViewController viewWillDisappear:YES]; [self.gameViewController.view removeFromSuperview]; this works fine for all screens but not for the gamescreen(well this is the only one with heaps of user-interaction) means the responsiveness of the iphone(when playing tones) gets really slow. The performance is fine when I display the gameview for the first time. it starts getting slower as soon as I add it to the menu-views-container-subviews again (addsubview) (basically open up a new game) any ideas what causes(or to get around) this? thanks heaps Best regards Tom

  Read the article

• Flash Without a SWF File?

  - by PeterAllenWebb

  Is there any way to embed Flash completely in HTML, without reference to an external SWF file? I ask because I would like to send an HTML file as an email attachment that the recipient will open in a browser and fill out as a form. The last step is that they will copy the result to their clipboard, paste it into a new message, and email it back. I cannot reliably copy to the clipboard with JavaScript because of the security issues, but there are simple Flash apps to add that capability. I know I could just display the response text (which will be Base64 encoded) to the recipient and have them copy/paste, but it would be nice to provide this small convenience to them. Also, so you are aware, the text is often too large to include in an email using mailto. Yes. This needs to be done via email. The users have slow, occasional satellite email access and no other data connection to the interwebs. To make things worse, I cannot make them install anything. It is a difficult situation.

  Read the article

• Reading numpy arrays outside of Python

  - by Abiel

  In a recent question I asked about the fastest way to convert a large numpy array to a delimited string. My reason for asking was because I wanted to take that plain text string and transmit it (over HTTP for instance) to clients written in other programming languages. A delimited string of numbers is obviously something that any client program can work with easily. However, it was suggested that because string conversion is slow, it would be faster on the Python side to do base64 encoding on the array and send it as binary. This is indeed faster. My question now is, (1) how can I make sure my encoded numpy array will travel well to clients on different operating systems and different hardware, and (2) how do I decode the binary data on the client side. For (1), my inclination is to do something like the following import numpy as np import base64 x = np.arange(100, dtype=np.float64) base64.b64encode(x.tostring()) Is there anything else I need to do? For (2), I would be happy to have an example in any programming language, where the goal is to take the numpy array of floats and turn them into a similar native data structure. Assume we have already done base64 decoding and have a byte array, and that we also know the numpy dtype, dimensions, and any other metadata which will be needed. Thanks.

  Read the article

• How do you efficiently bulk index lookups?

  - by Liron Shapira

  I have these entity kinds: Molecule Atom MoleculeAtom Given a list(molecule_ids) whose lengths is in the hundreds, I need to get a dict of the form {molecule_id: list(atom_ids)}. Likewise, given a list(atom_ids) whose length is in the hunreds, I need to get a dict of the form {atom_id: list(molecule_ids)}. Both of these bulk lookups need to happen really fast. Right now I'm doing something like: atom_ids_by_molecule_id = {} for molecule_id in molecule_ids: moleculeatoms = MoleculeAtom.all().filter('molecule =', db.Key.from_path('molecule', molecule_id)).fetch(1000) atom_ids_by_molecule_id[molecule_id] = [ MoleculeAtom.atom.get_value_for_datastore(ma).id() for ma in moleculeatoms ] Like I said, len(molecule_ids) is in the hundreds. I need to do this kind of bulk index lookup on almost every single request, and I need it to be FAST, and right now it's too slow. Ideas: Will using a Molecule.atoms ListProperty do what I need? Consider that I am storing additional data on the MoleculeAtom node, and remember it's equally important for me to do the lookup in the molecule-atom and atom-molecule directions. Caching? I tried memcaching lists of atom IDs keyed by molecule ID, but I have tons of atoms and molecules, and the cache can't fit it. How about denormalizing the data by creating a new entity kind whose key name is a molecule ID and whose value is a list of atom IDs? The idea is, calling db.get on 500 keys is probably faster than looping through 500 fetches with filters, right?

  Read the article

• Making GUI applications on Linux/Windows. What languages/tools to use?

  - by Javed Ahamed

  My student group and I are trying to continue working on a project we worked on this semester over the summer to become a professional, deployable app. We originally did it in Adobe AIR but it seems now that the computers this program will be running on will be very slow, maybe 600mhz and 128-256mb ram so flash just isn't going to cut it. It is basically a health diagnosis application that we will be shipping out to impoverished countries. Now comes the real question. We are wondering what language to rebuild our application in. It has to have a good gui builder associated with it, like adobe flex/air gui builder or visual studio's gui builder but the application should run on linux primarily, and if it can run on windows thats just a plus. We are all students too without really any outside help so whatever we decide to do this in there must be ample documentation available when we hit problems. Some things we have considered so far are using python and glade or c# and monodevelop, but again we really are not experts on any of this which is why I am asking for help as I would rather spend the time now choosing the right tools instead of wasting time down the line when we hit a roadblock. Thanks in advance!

  Read the article

• Lazy Sequences that "Look Ahead" for Project Euler Problem 14

  - by ivar

  I'm trying to solve Project Euler Problem 14 in a lazy way. Unfortunately, I may be trying to do the impossible: create a lazy sequence that is both lazy, yet also somehow 'looks ahead' for values it hasn't computed yet. The non-lazy version I wrote to test correctness was: (defn chain-length [num] (loop [len 1 n num] (cond (= n 1) len (odd? n) (recur (inc len) (+ 1 (* 3 n))) true (recur (inc len) (/ n 2))))) Which works, but is really slow. Of course I could memoize that: (def memoized-chain (memoize (fn [n] (cond (= n 1) 1 (odd? n) (+ 1 (memoized-chain (+ 1 (* 3 n)))) true (+ 1 (memoized-chain (/ n 2))))))) However, what I really wanted to do was scratch my itch for understanding the limits of lazy sequences, and write a function like this: (def lazy-chain (letfn [(chain [n] (lazy-seq (cons (if (odd? n) (+ 1 (nth lazy-chain (dec (+ 1 (* 3 n))))) (+ 1 (nth lazy-chain (dec (/ n 2))))) (chain (+ n 1)))))] (chain 1))) Pulling elements from this will cause a stack overflow for n2, which is understandable if you think about why it needs to look 'into the future' at n=3 to know the value of the tenth element in the lazy list because (+ 1 (* 3 n)) = 10. Since lazy lists have much less overhead than memoization, I would like to know if this kind of thing is possible somehow via even more delayed evaluation or queuing?

  Read the article

• Legitimate uses of the Function constructor

  - by Marcel Korpel

  As repeatedly said, it is considered bad practice to use the Function constructor (also see the ECMAScript Language Specification, 5th edition, § 15.3.2.1): new Function ([arg1[, arg2[, … argN]],] functionBody) (where all arguments are strings containing argument names and the last (or only) string contains the function body). To recapitulate, it is said to be slow, as explained by the Opera team: Each time […] the Function constructor is called on a string representing source code, the script engine must start the machinery that converts the source code to executable code. This is usually expensive for performance – easily a hundred times more expensive than a simple function call, for example. (Mark ‘Tarquin’ Wilton-Jones) Though it's not that bad, according to this post on MDC (I didn't test this myself using the current version of Firefox, though). Crockford adds that [t]he quoting conventions of the language make it very difficult to correctly express a function body as a string. In the string form, early error checking cannot be done. […] And it is wasteful of memory because each function requires its own independent implementation. Another difference is that a function defined by a Function constructor does not inherit any scope other than the global scope (which all functions inherit). (MDC) Apart from this, you have to be attentive to avoid injection of malicious code, when you create a new Function using dynamic contents. Lots of disadvantages and it is intelligible that ECMAScript 5 discourages the use of the Function constructor by throwing an exception when using it in strict mode (§ 13.1). That said, T.J. Crowder says in an answer that [t]here's almost never any need for the similar […] new Function(...), either, again except for some advanced edge cases. So, now I am wondering: what are these “advanced edge cases”? Are there legitimate uses of the Function constructor?

  Read the article

• FILE* issue PPU side code

  - by Cristina

  We are working on a homework on CELL programming for college and their feedback response to our questions is kinda slow, thought i can get some faster answers here. I have a PPU side code which tries to open a file passed down through char* argv[], however this doesn't work it cannot make the assignment of the pointer, i get a NULL. Now my first idea was that the file isn't in the correct directory and i copied in every possible and logical place, my second idea is that maybe the PPU wants this pointer in its LS area, but i can't deduce if that's the bug or not. So... My question is what am i doing wrong? I am working with a Fedora 7 SDK Cell, with Eclipse as an IDE. Maybe my argument setup is wrong tho he gets the name of the file correctly. Code on request: images_t *read_bin_data(char *name) { FILE *file; images_t *img; uint32_t *buffer; uint8_t buf; unsigned long fileLen; unsigned long i; //Open file file = (FILE*)malloc(sizeof(FILE)); file = fopen(name, "rb"); printf("[Debug]Opening file %s\n",name); if (!file) { fprintf(stderr, "Unable to open file %s", name); return NULL; } //....... } Main launch: int main(int argc,char* argv[]) { int i,img_width; int modif_this[4] __attribute__ ((aligned(16))) = {1,2,3,4}; images_t *faces, *nonfaces; spe_context_ptr_t ctxs[SPU_THREADS]; pthread_t threads[SPU_THREADS]; thread_arg_t arg[SPU_THREADS]; //intializare img_width img_width = atoi(argv[1]); printf("[Debug]Img size is %i\n",img_width); faces = read_bin_data(argv[3]); //....... } Thanks for the help.

  Read the article

• NULL-keys for key/value table

  - by user72185

  (Using Oracle) I have a table with key/value pairs like this: create table MESSAGE_INDEX ( KEY VARCHAR2(256) not null, VALUE VARCHAR2(4000) not null, MESSAGE_ID NUMBER not null ) I now want to find all the messages where key = 'someKey' and value is 'val1', 'val2' or 'val3' - OR value is null in which case there will be no entry in the table at all. This is to save space; there would be a large number of keys with null values if I stored them all. I think this works: SELECT message_id FROM message_index idx WHERE ((key = 'someKey' AND value IN ('val1', 'val2', 'val3')) OR NOT EXISTS (SELECT 1 FROM message_index WHERE key = 'someKey' AND idx.message_id = message_id)) But is is extremely slow. Takes 8 seconds with 700K records in message_index and there will be many more records and more search criteria when moving outside of my test environment. Primary key is key, value, message_id: add constraint PK_KEY_VALUE primary key (KEY, VALUE, MESSAGE_ID) And I added another index for message_id, to speed up searching for missing keys: create index IDX_MESSAGE_ID on MESSAGE_INDEX (MESSAGE_ID) I will be doing several of these key/value lookups in every search, not just one as shown above. So far I am doing them nested, where output id's of one level is the input to the next. E.g.: SELECT message_id from message_index WHERE (key/value compare) AND message_id IN ( SELECT ... and so on ) What can I do to speed this up?

  Read the article

• Grails or Play! for an ex-RoR developer ?

  - by Kedare

  Hello, I plan to begin learning a Java web framework (I love the Java API), I already used Rails and Django. I want something close to Java, but without all the complexity of J2EE. I've found 2 framework that could be good for me : Grails : Grails looks great, it use Groovy that is better than Java for web application (I think..), but it's slower, that use pure-java components (Hibernate, Strut, Spring), it looks pretty simple to deploy (send .war and it's ok !), the GSP is great ! It's a bit harder to debug (need to restart the server at each modification, and the stacktrace is a mix of Java and Groovy stack that is not always understandable..) Play! : This framework also looks great, it's faster than Grails (It's use directly Java), but I don't really like how it use Java, it modify the source code to transform the properties call as setXXX/getXXX, I'm not kind of that... The framework also have caching function that Grails don't (alreary) has. I don't really like the Template Engine. It's also easer to debug (no need to restart the server, and the stacktrace is clear) What do you recommend for ? I am looking for something easy to learn (I used a lot ruby and java, but a little bit java (But I love the Java API)), that is full featured (That's no a problem with all the Java Library availables, but if it's bundle and integrated I prefer), that scale and that is not too slow (faster than ruby), and if possible I would want something with a decent community to easily find support and answer to my questions ;) PS: No JRuby on Rails Thank you !

  Read the article

• Save memory in Python. How to iterate over the lines and save them efficiently with a 2million line

  - by skyl

  I have a tab-separated data file with a little over 2 million lines and 19 columns. You can find it, in US.zip: http://download.geonames.org/export/dump/. I started to run the following but with for l in f.readlines(). I understand that just iterating over the file is supposed to be more efficient so I'm posting that below. Still, with this small optimization, I'm using 10% of my memory on the process and have only done about 3% of the records. It looks like, at this pace, it will run out of memory like it did before. Also, the function I have is very slow. Is there anything obvious I can do to speed it up? Would it help to del the objects with each pass of the for loop? def run(): from geonames.models import POI f = file('data/US.txt') for l in f: li = l.split('\t') try: p = POI() p.geonameid = li[0] p.name = li[1] p.asciiname = li[2] p.alternatenames = li[3] p.point = "POINT(%s %s)" % (li[5], li[4]) p.feature_class = li[6] p.feature_code = li[7] p.country_code = li[8] p.ccs2 = li[9] p.admin1_code = li[10] p.admin2_code = li[11] p.admin3_code = li[12] p.admin4_code = li[13] p.population = li[14] p.elevation = li[15] p.gtopo30 = li[16] p.timezone = li[17] p.modification_date = li[18] p.save() except IndexError: pass if __name__ == "__main__": run()

  Read the article

< Previous Page | 264 265 266 267 268 269 270 271 272 273 274 275  | Next Page >