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• Why is Javascript's Math.floor the slowest way to calculate floor in Javascript?

  - by z5h

  I'm generally not a fan of microbenchmarks. But this one has a very interesting result. http://ernestdelgado.com/archive/benchmark-on-the-floor/ It suggests that Math.floor is the SLOWEST way to calculate floor in Javascript. ~~n, n|n, n&n all being faster. This seems pretty shocking as I would expect that people implementing Javascript in today's modern browsers would be some pretty smart people. Does floor do something important that the other methods fail to do? Is there any reason to use it?

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• SEO Google - Navigation Title vs. Page Heading

  - by louism

  Hi, i was wondering if anyone knows if theres a connection between what a navigation item is named and the page heading it goes to - does this have an impact on SEO? so for example, if i had in my navigation menu an item called About Us, but when you click it you come to a page with the heading Learn Who We Are (i.e. wrapped in [h1] heading tags) because there isnt an exact one-to-one match, is that a bad thing in terms of SEO? thanks

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• Alternate User select interface in django admin to reduce page size on large site?

  - by David Eyk

  I have a Django-based site with roughly 300,000 User objects. Admin pages for objects with a ForeignKey field to User take a very long time to load as the resulting form is about 6MB in size. Of course, the resulting dropdown isn't particularly useful, either. Are there any off-the-shelf replacements for handling this case? I've been googling for a snippet or a blog entry, but haven't found anything yet. I'd like to have a smaller download size and a more usable interface.

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• Drawbacks of Dynamic Query in Sqlserver 2005 ?

  - by KuldipMCA

  I have using the many dynamic Query in my database for the procedures because my filter is not fix so i have taken @filter as parameter and pass in the procedure. Declare @query as varchar(8000) Declare @Filter as varchar(1000) set @query = 'Select * from Person.Address where 1=1 and ' + @Filter exec(@query) Like that my filter contain any Field from the table for comparison. It will affect my performance or not ? is there any alternate way to achieve this type of things

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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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• 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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• 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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• 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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• Avoid the use of loops (for) with R

  - by albergali

  Hi, I'm working with R and I have a code like this: i<-1 j<-1 for (i in 1:10) for (j in 1:100) if (data[i] == paths[j,1]) cluster[i,4] <- paths[j,2] where : data is a vector with 100 rows and 1 column paths is a matrix with 100 rows and 5 columns cluster is a matrix with 100 rows and 5 columns My question is: how could I avoid the use of "for" loops to iterate through the matrix? I don't know whether apply functions (lapply, tapply...) are useful in this case. This is a problem when j=10000 for example, because execution time is very long. Thank you

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• Resize an image and maintain quality?

  - by JasonS

  Hi, I have a problem with resizing images. What happens is that if you upload a file larger than the stated parameters, the image is cropped, then saved at 100% quality. So if I upload a large jpeg which is 272Kb. The image is cropped by 100 odd pixels. The file size then goes up to 1.2Mb. We are saving images at a 100% quality. I assume that this is what is causing the problem. The image is exported from Photoshop at 30% quality which reduces the file size. Resaving the image at 100% quality creates the same image but I assume with a lot of redundant file data. Has anyone encountered this before? Does anyone have a solution? This is what we are using. $source_im = imagecreatefromjpeg ($file); $dest_im = imagecreatetruecolor ($newsize_x, $newsize_y); imagecopyresampled ( $dest_im, $source_im, 0, 0, $offset_x, $offset_y, $newsize_x, $newsize_y, $sourceWidth, $sourceHeight ); imagedestroy ($source_im); if ($greyscale) { $dest_im = $this->imageconvertgreyscale ($dest_im); } imagejpeg($dest_im, $save_to_file, $quality); break;

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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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• Which fieldtype is best for storing PRICE values?

  - by BerggreenDK

  Hi there I am wondering whats the best "price field" in MSSQL for a shoplike structure? Looking at this overview: http://www.teratrax.com/sql_guide/data_types/sql_server_data_types.html We have datatypes called money, smallmoney, then we have decimal/numeric and lastly float and real Name, memory/disk-usage and value ranges: Money: 8 bytes (values: -922,337,203,685,477.5808 to +922,337,203,685,477.5807) Smallmoney: 4 bytes (values: -214,748.3648 to +214,748.3647) Decimal: 9 [default, min. 5] bytes (values: -10^38 +1 to 10^38 -1 ) Float: 8 bytes (values: -1.79E+308 to 1.79E+308 ) Real: 4 bytes (values: -3.40E+38 to 3.40E+38 ) My question is: is it really wise to store pricevalues in those types? what about eg. INT? Int: 4 bytes (values: -2,147,483,648 to 2,147,483,647) Lets say a shop uses dollars, they have cents, but I dont see prices being $49.2142342 so the use of a lot of decimals showing cents seems waste of SQL bandwidth. Secondly, most shops wouldn't show any prices near 200.000.000 (not in normal webshops at least... unless someone is trying to sell me a famous tower in Paris) So why not go for an int? An int is fast, its only 4 bytes and you can easily make decimals, by saving values in cents instead of dollars and then divide when you present the values. The other approach would be to use smallmoney which is 4 bytes too, but this will require the math part of the CPU to do the calc, where as Int is integer power... on the downside you will need to divide every single outcome. Are there any "currency" related problems with regionalsettings when using smallmoney/money fields? what will these transfer too in C#/.NET ? Any pros/cons? Go for integer prices or smallmoney or some other? Whats does your experience tell?

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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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• Should Python import statements always be at the top of a module?

  - by Adam J. Forster

  PEP 08 states: Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants. However if the class/method/function that I am importing is only used in rare cases, surely it is more efficient to do the import when it is needed? Isn't this: class SomeClass(object): def not_often_called(self) from datetime import datetime self.datetime = datetime.now() more efficient than this? from datetime import datetime class SomeClass(object): def not_often_called(self) self.datetime = datetime.now()

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• How to increase query speed without using full-text search?

  - by andre matos

  This is my simple query; By searching selectnothing I'm sure I'll have no hits. SELECT nome_t FROM myTable WHERE nome_t ILIKE '%selectnothing%'; This is the EXPLAIN ANALYZE VERBOSE Seq Scan on myTable (cost=0.00..15259.04 rows=37 width=29) (actual time=2153.061..2153.061 rows=0 loops=1) Output: nome_t Filter: (nome_t ~~* '%selectnothing%'::text) Total runtime: 2153.116 ms myTable has around 350k rows and the table definition is something like: CREATE TABLE myTable ( nome_t text NOT NULL, ) I have an index on nome_t as stated below: CREATE INDEX idx_m_nome_t ON myTable USING btree (nome_t); Although this is clearly a good candidate for Fulltext search I would like to rule that option out for now. This query is meant to be run from a web application and currently it's taking around 2 seconds which is obviously too much; Is there anything I can do, like using other index methods, to improve the speed of this query?

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• Feedback on Optimizing C# NET Code Block

  - by Brett Powell

  I just spent quite a few hours reading up on TCP servers and my desired protocol I was trying to implement, and finally got everything working great. I noticed the code looks like absolute bollocks (is the the correct usage? Im not a brit) and would like some feedback on optimizing it, mostly for reuse and readability. The packet formats are always int, int, int, string, string. try { BinaryReader reader = new BinaryReader(clientStream); int packetsize = reader.ReadInt32(); int requestid = reader.ReadInt32(); int serverdata = reader.ReadInt32(); Console.WriteLine("Packet Size: {0} RequestID: {1} ServerData: {2}", packetsize, requestid, serverdata); List<byte> str = new List<byte>(); byte nextByte = reader.ReadByte(); while (nextByte != 0) { str.Add(nextByte); nextByte = reader.ReadByte(); } // Password Sent to be Authenticated string string1 = Encoding.UTF8.GetString(str.ToArray()); str.Clear(); nextByte = reader.ReadByte(); while (nextByte != 0) { str.Add(nextByte); nextByte = reader.ReadByte(); } // NULL string string string2 = Encoding.UTF8.GetString(str.ToArray()); Console.WriteLine("String1: {0} String2: {1}", string1, string2); // Reply to Authentication Request MemoryStream stream = new MemoryStream(); BinaryWriter writer = new BinaryWriter(stream); writer.Write((int)(1)); // Packet Size writer.Write((int)(requestid)); // Mirror RequestID if Authenticated, -1 if Failed byte[] buffer = stream.ToArray(); clientStream.Write(buffer, 0, buffer.Length); clientStream.Flush(); } I am going to be dealing with other packet types as well that are formatted the same (int/int/int/str/str), but different values. I could probably create a packet class, but this is a bit outside my scope of knowledge for how to apply it to this scenario. If it makes any difference, this is the Protocol I am implementing. http://developer.valvesoftware.com/wiki/Source_RCON_Protocol

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• Fast format conversion open source library

  - by KindDragon

  Can someone advise me open source format conversion library? Optimized for SSE, SSE2. Formats for conversion: I420, YUY2, RGB(16-bit, 32-bit). I found only VirtualDub Kasumi library.

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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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• Where is the bottleneck in this code?

  - by Mikhail

  I have the following tight loop that makes up the serial bottle neck of my code. Ideally I would parallelize the function that calls this but that is not possible. //n is about 60 for (int k = 0;k < n;k++) { double fone = z[k*n+i+1]; double fzer = z[k*n+i]; z[k*n+i+1]= s*fzer+c*fone; z[k*n+i] = c*fzer-s*fone; } Are there any optimizations that can be made such as vectorization or some evil inline that can help this code? I am looking into finding eigen solutions of tridiagonal matrices. http://www.cimat.mx/~posada/OptDoglegGraph/DocLogisticDogleg/projects/adjustedrecipes/tqli.cpp.html

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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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• Vector [] vs copying

  - by sak

  What is faster and/or generally better? vector<myType> myVec; int i; myType current; for( i = 0; i < 1000000; i ++ ) { current = myVec[ i ]; doSomethingWith( current ); doAlotMoreWith( current ); messAroundWith( current ); checkSomeValuesOf( current ); } or vector<myType> myVec; int i; for( i = 0; i < 1000000; i ++ ) { doSomethingWith( myVec[ i ] ); doAlotMoreWith( myVec[ i ] ); messAroundWith( myVec[ i ] ); checkSomeValuesOf( myVec[ i ] ); } I'm currently using the first solution. There are really millions of calls per second and every single bit comparison/move is performance-problematic.

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• Delphi fast large bitmap creation (without clearing)

  - by Ritsaert Hornstra

  When using the TBitmap wrapper for a GDI bitmap from the unit Graphics I noticed it will always clear out the bitmap (using a PatBlt call) when setting up a bitmap with SetSize( w, h ). When I copy in the bits later on (see routine below) it seems ScanLine is the fastest possibility and not SetDIBits. function ToBitmap: TBitmap; var i, N, x: Integer; S, D: PAnsiChar; begin Result := TBitmap.Create(); Result.PixelFormat := pf32bit; Result.SetSize( width, height ); S := Src; D := Result.ScanLine[ 0 ]; x := Integer( Result.ScanLine[ 1 ] ) - Integer( D ); N := width * sizeof( longword ); for i := 0 to height - 1 do begin Move( S^, D^, N ); Inc( S, N ); Inc( D, x ); end; end; The bitmaps I need to work with are quite large (150MB of RGB memory). With these iomages it takes 150ms to simply create an empty bitmap and a further 140ms to overwrite it's contents. Is there a way of initializing a TBitmap with the correct size WITHOUT initializing the pixels itself and leaving the memory of the pixels uninitialized (eg dirty)? Or is there another way to do such a thing. I know we could work on the pixels in place but this still leaves the 150ms of unnessesary initializtion of the pixels.

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• C# question to ex-C++/ASM guys. Speed optimisation

  - by maxima120

  Which in C# compiled for x64 is faster? a. int * int; b. if(int < 0) int = -int; c. Math.Abs(int) I need pure theoretical answer. Please do not tell me to write loop and measure it with stopwatch. Thanks

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• NHibernate, each property is filled with a different select statement

  - by Eitan

  I'm retrieving a list of nhibernate entites which have relationships to other tables/entities. I've noticed instead of NHibernate performing JOINS and populating the properties, it retrieves the entity and then calls a select for each property. For example if a user can have many roles and I retrieve a user from the DB, Nhibernate retrieves the user and then populates the roles with another select statement. The problem is that I want to retrieve oh let's say a list of products which have various many-to-many relationships and relationships to items which have their own relationships. In the end I'm left with over a thousand DB calls to retrieve a list of 30 products. Thanks. I've also set default lazy loading to false because whenever I save the list of entities to a session, I get an error when trying to retrieve it on another page: LazyInitializationException: could not initialize proxy If anybody could shed any light I would truly appreciate it. Thanks. Eitan

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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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