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• Efficient implementation of natural logarithm (ln) and exponentiation

  - by Donotalo

  Basically, I'm looking for implementation of log() and exp() functions provided in C library <math.h>. I'm working with 8 bit microcontrollers (OKI 411 and 431). I need to calculate Mean Kinetic Temperature. The requirement is that we should be able to calculate MKT as fast as possible and with as little code memory as possible. The compiler comes with log() and exp() functions in <math.h>. But calling either function and linking with the library causes the code size to increase by 5 Kilobytes, which will not fit in one of the micro we work with (OKI 411), because our code already consumed ~12K of available ~15K code memory. The implementation I'm looking for should not use any other C library functions (like pow(), sqrt() etc). This is because all library functions are packed in one library and even if one function is called, the linker will bring whole 5K library to code memory.

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• Is Sphinx better than LaTex in writing manuals/books?

  - by Masi

  Only a few people recommended to use Sphinx at the beginning of the year. Sphinx has developed rather fast recently. I noted today that Sage has made a change from direct editing with LaTex to Sphinx. This is evident in William Stein's answer on 2nd April about Sage's tutorial The tutorial is not a latex document anymore. It's an entirely different Sphinx document that can output pdf. It suggests me that Sphinx may be at a level such that it is suitable for me. Is Sphinx better than LaTex in writing manuals/books?

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• Quick way to do data lookup in PHP

  - by Ghostrider

  I have a data table with 600,000 records that is around 25 megabytes large. It is indexed by a 4 byte key. Is there a way to find a row in such dataset quickly with PHP without resorting to MySQL? The website in question is mostly static with minor PHP code and no database dependencies and therefore fast. I would like to add this data without having to use MySQL if possible. In C++ I would memory map the file and do a binary search in it. Is there a way to do something similar in PHP?

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• Need help on nested loop of queries in php and mysql?

  - by mysqllearner

  Hi, I am trying to get do this: <?php $good_customer = 0; $q = mysql_query("SELECT user FROM users WHERE activated = '1'"); // this gives me about 40k users while($r = mysql_fetch_assoc($q)){ $money_spent = 0; $user = $r['user']; // Do queries on another 20 tables for($i = 1; $i<=20 ; $i++){ $tbl_name = 'data' . $i; $q2 = mysql_query("SELECT money_spent FROM $tbl_name WHERE user = '{$user}'"); while($r2 = mysql_fetch_assoc($q2)){ $money_spend += $r2['money_spent']; } if($money_spend > 1000000){ $good_customer += 1; } } } This is just an example. I am testing on localhost, for single user, it returns very fast. But when I try 1000, it takes forever, not even mentioned 40k users. Anyway to optimise/improve this code? EDIT: By the way, each of the others 20 tables has ~20 - 40k records

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• Trying to find a good javascript function for hmac-sha1

  - by Darxval

  So i have been searching the web for a javascript source for an Hmac-sha1 algorithm. I saw Crypto's but i cant seem to get it to work, mainly because it has no idea what crypto means. (i copied the .js script functions into my script file) http://code.google.com/p/crypto-js/ I have my base64 encoded function already. that i got from here: http://nerds-central.blogspot.com/2007/01/fast-scalable-javascript-and-vbscript.html btw this for a twitter application using the new OAuth system. any help or links to where i can find anything on this would be helpful If you need me to elaborate let me know. thank you!

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• How to store and compare time-zone sensitive times

  - by Chad Moran

  I have a data structure where an entity has times stored as an int (minutes into the day) for fast comparison. The entity also has a Foreign Key reference back to a TimeZone table which contains the .NET CLR ID Name and it's Standard Time/Daylight Time acronyms. Since this information is stored as time-zone insensitive - I was wondering how in LINQ to SQL I could convert this into a UTC DateTime for comparison against other times that will be in UTC. Just to be clear this conversion has to be done server-side so that I can execute filtering on the SQL Server and not the client. I am using .NET 3.5 SP1 and SQL Server 2008.

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• Python IPC, popen too slow

  - by UnableToLoad

  i need to run a subprocess (./myProgram) form python script and get output, actually i do this: import subprocess proc = subprocess.Popen('./generate_out', shell=False, stdout=subprocess.PIPE, ) while proc.poll() is None: out = proc.stdout.readline() data = doStuff(out) print(data) but is slow, sometimes pass a lot of time between the output produced by ./generate_out and the print(data), knowing that my doStuff() function is very fast, i think there is some buffer slowing down my pipe... Notes: ./generate_out, generates potentially an unlimited number of lines of finite length each. It seems that when too few chars are put in the pipe between the two processes nothing happens, then when enough is produced i get a huge print (non the expected behaviour!) sometimes i wait many seconds (10-20 and more) between generate_out print and python print) what can i do? maybe communicate() is faster? anithing else? Thank you a lot!

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• What the difference between zend framework and Wordpress as framework ?

  - by justjoe

  i only know wordpress and start to seek another alternative framework, zend. i heard hearsay that zend's better from others framework. if you're "a serous coder", or try to act like one, you need to use it on building your web app. some said zend is better. But it's subjective. It's fast ans secure. But nobody tell me the reason or at leas compare it with with wordpress. ultimate question : Do zend have theme or plugin just like wordpress ? any hint will be helpful

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• A 110 kb .NET 4.0 app needs 10 seconds for a cold start, thats not acceptable !

  - by msfanboy

  Hello, I am using the .NET 4.0 client profile for my app and I run a dual core with 4 GB Ram and a fast hard disk. nothing big is done at the start just showing a generic List in a wpf listview. How can I make the cold start faster of my assembly ? I have done now again a cold start and run the windowsapplication.exe in my \obj\x86\Debug folder and my harddisk run like hell and it took 10,5 seconds ??? What is wrong? The warm start after the cold one took 1 second. Java 6 apps has not that problem, not at all just to compare...

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• Multi-threaded downloader in C# question

  - by blez

  Currently I have multi-threaded downloader class that uses HttpWebRequest/Response. All works fine, it's super fast, BUT.. the problem is that the data needs to be streamed while it's downloading to another app. That means that it must be streamed in the right order, the first chunk first, and then the next in the queue. Currently my downloader class is sync and Download() returns byte[]. In my async multi-threaded class I make for example, list with 4 empty elements (for slots) and I pass each index of the slot to each thread using the Download() function. That simulates synchronization, but that's not what I need. How should I do the queue thing, to make sure the data is streamed as soon as the first chunk start downloading.

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• How do you make Python wait so that you can read the output?

  - by anonnoir

  I've always been a heavy user of Notepad2, as it is fast, feature-rich, and supports syntax highlighting. Recently I've been using it for Python. My problem: when I finish editing a certain Python source code, and try to launch it, the screen disappears before I can see the output pop up. Is there any way for me to make the results wait so that I can read it, short of using an input() or time-delay function? Otherwise I'd have to use IDLE, because of the output that stops for you to read. (My apologies if this question is a silly one, but I'm very new at Python and programming in general.)

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• Teaching a kid to type in order to start programming

  - by at

  My 5 year old wants to start programming, but he doesn't yet know how to type without looking for each letter 1 at a time. I know it's going to frustrate him to go so slow because of his typing speed. And it's not going to be fun looking for all the letters constantly... So what's the best way to get him to type fast? Clearly he'll need to type a lot of punctuation like semicolons, colons and symbols. So his little hands will have to get used to spreading over the keyboard... I did some google searches and found some very poor looking apps that focused on the letters.

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• PHP / javascript live chat using too much bandwidth

  - by David

  So I am learning about javascript, so I am making a live chat system with PHP and javascript. I have it so the javascript refreshes the log (each message gets logged in a file on the server), and it refreshes every second. Im using firebug to monitor the resource usage, and I see under the net tab each times its updated, and the bytes add up really fast. I know I can change it to update less, but is there a way that when a user on the other end I'm talking to, when the send a message, it gets sent to the server, then an alert gets sent to me saying that the chatlog needs to update somehow. That way it only updates when the log is updated. let me know, thanks

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• Oracle, slow performance when using sub select

  - by Wyass

  I have a view that is very slow if you fetch all rows. But if I select a subset (providing an ID in the where clause) the performance is very good. I cannot hardcode the ID so I create a sub select to get the ID from another table. The sub select only returns one ID. Now the performance is very slow and it seems like Oracle is evaluating the whole view before using the where clause. Can I somehow help Oracle so SQL 2 and 3 have the same performance? I’m using Oracle 10g 1 slow select * from ci.my_slow_view 2 fast select * from ci.my_slow_view where id = 1; 3 slow select * from ci.my_slow_view where id in (select id from active_ids)

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• Help with concept - filters and number of items

  - by dreamer

  Please check http://www.alibaba.com/catalogs/cid/702/Laptops.html they have nice filter here with number of items for each. Note one detail - they have locations here. Same thing on olx.com - location and number of items for each category. Now imagine I have tables: [products] (Id, Name, CategoryId, LocationId) [Categories] (Id,Name) [Location] (Id, Name) My question how can I do the same, cause count things even with caching looks expensive? And they give results pretty fast... Please advice with possible ways to do that in ASP.NET, C#, MVC, MS SQL, but avoice simple answers like "count and change" Thank you in advance.

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• Retrieving data from database. Retrieve only when needed or get everything?

  - by RHaguiuda

  I have a simple application to store Contacts. This application uses a simple relational database to store Contact information, like Name, Address and other data fields. While designing it, I question came to my mind: When designing programs that uses databases, should I retrieve all database records and store them in objects in my program, so I have a very fast performance or I should always gather data only when required? Of course, retrieving all data can only be done if it`s not too many, but do you use this approach when you make sure that the database will be small (< 300 records for example)? I have designed once a similar application that fetches data only when needed, but that was slow (using a Access database). Thanks for all help.

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• C++ union assignment, is there a good way to do this?

  - by Sqeaky

  I am working on a project with a library and I must work with unions. Specifically I am working with SDL and the SDL_Event union. I need to make copies of the SDL_Events, and I could find no good information on overloading assignment operators with unions. Provided that I can overload the assignment operator, should I manually sift through the union members and copy the pertinent members or can I simply come some members (this seems dangerous to me), or maybe just use memcpy() (this seems simple and fast, but slightly dangerous)? If I can't overload operators what would my best options be from there? I guess I could make new copies and pass around a bunch of pointers, but in this situation I would prefer not to do that. Any ideas welcome!

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• two android threads and not synchronized data

  - by Sponge

  i have a (perhaps stupid) question: im using 2 threads, one is writing floats and one is reading this floats permanently. my question is, what could happen worse when i dont synchronize them? it would be no problem if some of the values would not be correct because they switch just a little every write operation. im running the application this way at the moment and dont have any problems so i want to know what could happen worse? a read/write conflict would cause a number like 12345 which is written to 54321 and red at the same time appear for example as 54345 ? or could happen something worse? (i dont want to use synchronization to keep the code as fast as possible)

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• MPMoviePlayerController seems to make 2 calls for each movie

  - by user76328

  I seem to have an issue where an iphone app using the MPMoviePlayerController seems to make 2 calls to the server for each video it wants to play back. This occurs with iphone 3.x OS and libraries but not with iphone 2.x. I know that iphone does progressive download and will make multiple 206 requests, etc. but as far as our back end is concerned the player appears to make 2 separate sessions. This only appears to be an issue with iPhone native apps and not iphone videos played through safari. Additional info from apple: iPhone OS 3.0 added support for streaming audio and video over HTTP, and MPMoviePlayerController must validate the media before playback to determine if it is streaming content or progressively downloaded content. This is the delay you are experiencing. On a fast network, the delay should be minimized. Is this double check causing 2 sessions be created for each video request? Any one else seeing same issue? Is there a remedy?

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• How to handle large table in MySQL ?

  - by Frantz Miccoli

  I've a database used to store items and properties about these items. The number of properties is extensible, thus there is a join table to store each property associated to an item value. CREATE TABLE `item_property` ( `property_id` int(11) NOT NULL, `item_id` int(11) NOT NULL, `value` double NOT NULL, PRIMARY KEY (`property_id`,`item_id`), KEY `item_id` (`item_id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci; This database has two goals : storing (which has first priority and has to be very quick, I would like to perform many inserts (hundreds) in few seconds), retrieving data (selects using item_id and property_id) (this is a second priority, it can be slower but not too much because this would ruin my usage of the DB). Currently this table hosts 1.6 billions entries and a simple count can take up to 2 minutes... Inserting isn't fast enough to be usable. I'm using Zend_Db to access my data and would really be happy if you don't suggest me to develop any php side part. Thanks for your advices !

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• Best indexing strategy for several varchar columns in Postgres

  - by Corey

  I have a table with 10 columns that need to be searchable (the table itself has about 20 columns). So the user will enter query criteria for at least one of the columns but possibly all ten. All non-empty criteria is then put into an AND condition Suppose the user provided non-empty criteria for column1 and column4 and column8 the query would be: select * from the_table where column1 like '%column1_query%' and column4 like '%column4_query%' and column8 like '%column8_query%' So my question is: am I better off creating 1 index with 10 columns? 10 indexes with 1 column each? Or do I need to find out what sets of columns are queried together frequently and create indexes for them (an index on cols 1,4 and 8 in the case above). If my understanding is correct a single index of 10 columns would only work effectively if all 10 columns are in the condition. Open to any suggestions here, additionally the rowcount of the table is only expected to be around 20-30K rows but I want to make sure any and all searches on the table are fast. Thanks!

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• Is Python good for highload web projects?

  - by Vitali Fokin

  Hello! I decidet to start my own web project. It should be highload project, and I can't decide which technologies should I use. I'm good in ASP.NET MVC, but I like languages like Python more than C#. I read a lot about Python and Django/Pylons/etc but I didn't find any good examples of highload projects on python. So, the question is: Is Python good for highload project? Is it enough fast? And if it is, are python frameworks like django/pylons/etc good for this? Or asp.net mvc will be better choice? PS, I'm not interesting in Java, Ruby and PHP :) So, I'm choosing only between Python + django/pylons/etc and asp.net mvc. Thanks in advance. Please, don't make holywars :)

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• Annoying Bug in banner cycle

  - by Davemof

  I have created a rotating banner script for a new site I'm developing View banner here(it rotates every 10 seconds) Unfortunately to the transition seems to be a biut buggy, and the image will fade out, show the same image again and then fade in the new one. I think I have made a simple error somewhere, but can't figure out where it is. the code used to cycle the banners is: In document ready: if ($('.home').length > 0){ $('<img width="100%" />').attr('src', '/assets/img/backgrounds/home/hero'+homecount+'.jpg').load(function(){ $('.hero').append( $(this) ); $('.hero img').fadeIn('medium').delay(10000).fadeOut('slow', loopImages); setHeroHeight(); }); } Outside document ready: function loopImages(){ homecount = homecount+1; if (homecount > 5){ homecount = 1; } $('.hero img') .attr('src', '/assets/img/backgrounds/home/hero'+homecount+'.jpg') .load(function(){ $('.hero img').fadeIn('fast')}).delay(10000).fadeOut('slow', loopImages); } Any help would be greatly appreciated Thanks Dave

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• Dynamically generating high performance functions in clojure

  - by mikera

  I'm trying to use Clojure to dynamically generate functions that can be applied to large volumes of data - i.e. a requirement is that the functions be compiled to bytecode in order to execute fast, but their specification is not known until run time. e.g. suppose I specify functions with a simple DSL like: (def my-spec [:add [:multiply 2 :param0] 3]) I would like to create a function compile-spec such that: (compile-spec my-spec) Would return a compiled function of one parameter x that returns 2x+3. What is the best way to do this in Clojure?

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• Treating a fat webservice in .net 3.5 c#

  - by Chris M

  I'm dealing with an obese 3rd party webservice that returns about 3mb of data for a simple search results, about 50% of the data in that response is junk. Would it make sense then to remap this data to my own result object and ditch the response so I'm storing 1-2 mb in memory for filtering and sorting rather than using the web-responses own object and using 2-4 or am I missing a point? So far I've been accessing the webservice from a separate project and using a new class to provide the interaction and to handle the persistence so my project looks like this |- Web (mvc2 proj) |- DAL (database/storage fluent-nhibernate) |- SVCGateway (interaction layer + webservice related models) |- Services -------------- |- Tests |- Specs I'm trying to make the application behave fast and I also need to store the result set temporarily in case a customer goes to view the product and wants to go back to the results. (Service returns only 500 of possible 14K results). So basically I'm looking for confirmation that I'm doing the right thing in pushing the results into my own objects or if I'm breaking some rule or even if there's a better way of handling it. Thanks

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