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• Recommended textbook for machine-level programming?

  - by Norman Ramsey

  I'm looking at textbooks for an undergraduate course in machine-level programming. If the perfect book existed, this is what it would look like: Uses examples written in C or assembly language, or both. Covers machine-level operations such as two's-complement integer arithmetic, bitwise operations, and floating-point arithmetic. Explains how caches work and how they affect performance. Explains machine instructions or assembly instructions. Bonus if the example assembly language includes x86; triple bonus if it includes x86-64 (aka AMD64). Explains how C values and data structures are represented using hardware registers and memory. Explains how C control structures are translated into assembly language using conditional and unconditional branch instructions. Explains something about procedure calling conventions and how procedure calls are implemented at the machine level. Books I might be interested in would probably have the words "machine organization" or "computer architecture" in the title. Here are some books I'm considering but am not quite happy with: Computer Systems: A Programmer's Perspective by Randy Bryant and Dave O'Hallaron. This is quite a nice book, but it's a book for a broad, shallow course in systems programming, and it contains a great deal of material my students don't need. Also, it is just out in a second edition, which will make it expensive. Computer Organization and Design: The Hardware/Software Interface by Dave Patterson and John Hennessy. This is also a very nice book, but it contains way more information about how the hardware works than my students need. Also, the exercises look boring. Finally, it has a show-stopping bug: it is based very heavily on MIPS hardware and the use of a MIPS simulator. My students need to learn how to use DDD, and I can't see getting this to work on a simulator. Not to mention that I can't see them cross-compiling their code for the simulator, and so on and so forth. Another flaw is that the book mentions the x86 architecture only to sneer at it. I am entirely sympathetic to this point of view, but news flash! You guys lost! Write Great Code Vol I: Understanding the Machine by Randall Hyde. I haven't evaluated this book as thoroughly as the other two. It has a lot of what I need, but the translation from high-level language to assembler is deferred to Volume Two, which has mixed reviews. My students will be annoyed if I make them buy a two-volume series, even if the price of those two volumes is smaller than the price of other books. I would really welcome other suggestions of books that would help students in a class where they are to learn how C-language data structures and code are translated to machine-level data structures and code and where they learn how to think about performance, with an emphasis on the cache.

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• java.util.zip - ZipInputStream v.s. ZipFile

  - by lucho

  Hello, community! I have some general questions regarding the java.util.zip library. What we basically do is an import and an export of many small components. Previously these components were imported and exported using a single big file, e.g.: <component-type-a id="1"/> <component-type-a id="2"/> <component-type-a id="N"/> <component-type-b id="1"/> <component-type-b id="2"/> <component-type-b id="N"/> Please note that the order of the components during import is relevant. Now every component should occupy its own file which should be externally versioned, QA-ed, bla, bla. We decided that the output of our export should be a zip file (with all these files in) and the input of our import should be a similar zip file. We do not want to explode the zip in our system. We do not want opening separate streams for each of the small files. My current questions: Q1. May the ZipInputStream guarantee that the zip entries (the little files) will be read in the same order in which they were inserted by our export that uses ZipOutputStream? I assume reading is something like: ZipInputStream zis = new ZipInputStream(new BufferedInputStream(fis)); ZipEntry entry; while((entry = zis.getNextEntry()) != null) { //read from zis until available } I know that the central zip directory is put at the end of the zip file but nevertheless the file entries inside have sequential order. I also know that relying on the order is an ugly idea but I just want to have all the facts in mind. Q2. If I use ZipFile (which I prefer) what is the performance impact of calling getInputStream() hundreds of times? Will it be much slower than the ZipInputStream solution? The zip is opened only once and ZipFile is backed by RandomAccessFile - is this correct? I assume reading is something like: ZipFile zipfile = new ZipFile(argv[0]); Enumeration e = zipfile.entries();//TODO: assure the order of the entries while(e.hasMoreElements()) { entry = (ZipEntry) e.nextElement(); is = zipfile.getInputStream(entry)); } Q3. Are the input streams retrieved from the same ZipFile thread safe (e.g. may I read different entries in different threads simultaneously)? Any performance penalties? Thanks for your answers!

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• Memory leak appears only when multiprocessing

  - by Sandro

  I am trying to use python's multiprocessing library to hopefully gain some performance. Specifically I am using its map function. Now, for some reason when I swap it out with its single threaded counterpart I don't get any memory leaks over time. But using the multiprocessing version of map causes my memory to go through the roof. For the record I am doing something which can easily hog up loads of memory, but what would the difference be between the two to cause such a stark difference?

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• What is the right data type for calculations in Java

  - by Raju

  Should we use double or BigDecimal for calculations in Java? How much is the overhead in terms of performance for BigDecimal as compared to double?

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• asp.net mvc rhino mocks mocking httprequest values

  - by Matthew

  Hi Is there a way to mock request params, what is the best approach when testing to create fake request values in order to run a test would some thing like this work? _context = MockRepository.GenerateStub<HttpContext>(); request = MockRepository.GenerateStub<HttpRequest>(); var collection = new NameValueCollection(); collection.Add("", ""); SetupResult.For(request.Params).Return(collection); SetupResult.For(_context.Request).Return(request);

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• PostgreSQL or MS SQL Server?

  - by mmiika

  I'm considering using PostgreSQL with a .Net web app. Basically 3 reasons: Mature Geo Queries Small footprint + Linux Price I'm wondering a bit about tools though, SQL Server Profiler and query plans and performance monitors have been helpful. How is this world with Postgres? Some other things I should consider? Edit: Will most likely use NHibernate as ORM

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• best option to create simple website mockup with navigation

  - by Buzzer

  I'm trying to put together a static html website with full navigation. In other words, I want the user to click some links and images and actually be taken to another page. I'm a developer so I know how to do this in frameworks like ASP.Net MVC and grails. However, for this particular case, I just want to quickly mock up the UI and provide simple navigation so I can do some user testing. Can anyone advice on how to do this? Thanks,

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• Concise way to getattr() and use it if not None in Python

  - by MTsoul

  I am finding myself doing the following a bit too often: attr = getattr(obj, 'attr', None) if attr is not None: attr() # Do something, either attr(), or func(attr), or whatever else: # Do something else Is there a more pythonic way of writing that? Is this better? (At least not in performance, IMO.) try: obj.attr() # or whatever except AttributeError: # Do something else

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• users see my SMS messages as coming from '1010100001'

  - by John Leonard

  In my application, I ask the user to enter their cell and select their provider. I append the provider's email and create the message and fire via php.mail() The problem is that no matter what the header info is, the message comes from '1010100001' on some phones (like AT&T and the iPhone). When testing on my Verizon phone, I get the proper email address as the sender. Any idea how I can send a clearer message?

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• Limit on amount of generic parameters in .NET?

  - by thr

  Is there a limit on the amount of generic parameters you can have on a type in .NET? Either hard limit (like 32) or a soft limit (where it somehow effects performance to much, etc.) What I'm referring to is: class Foo<T0, T2, T3, T4, etc.> { }

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• what is the proper way to do logging in csv file?

  - by user2003548

  i want to log some information of every single request send to a busy http server in a formatted form,use log module would create some thing i don't want to: [I 131104 15:31:29 Sys:34] i think of csv format but i don't know how to customize it,and python got csv module,but read the manual import csv with open('some.csv', 'w', newline='') as f: writer = csv.writer(f) writer.writerows(someiterable) since it would open and close a file each time, i am afraid in this way would slow down the whole server performance, what could i do?

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• Strange behavior of move with strings

  - by Umair Ahmed

  I am testing some enhanced string related functions with which I am trying to use move as a way to copy strings around for faster, more efficient use without delving into pointers. While testing a function for making a delimited string from a TStringList, I encountered a strange issue. The compiler referenced the bytes contained through the index when it was empty and when a string was added to it through move, index referenced the characters contained. Here is a small downsized barebone code sample:- unit UI; interface uses System.SysUtils, System.Types, System.UITypes, System.Rtti, System.Classes, System.Variants, FMX.Types, FMX.Controls, FMX.Forms, FMX.Dialogs, FMX.Layouts, FMX.Memo; type TForm1 = class(TForm) Results: TMemo; procedure FormCreate(Sender: TObject); end; var Form1: TForm1; implementation {$R *.fmx} function StringListToDelimitedString ( const AStringList: TStringList; const ADelimiter: String ): String; var Str : String; Temp1 : NativeInt; Temp2 : NativeInt; DelimiterSize : Byte; begin Result := ' '; Temp1 := 0; DelimiterSize := Length ( ADelimiter ) * 2; for Str in AStringList do Temp1 := Temp1 + Length ( Str ); SetLength ( Result, Temp1 ); Temp1 := 1; for Str in AStringList do begin Temp2 := Length ( Str ) * 2; // Here Index references bytes in Result Move ( Str [1], Result [Temp1], Temp2 ); // From here the index seems to address characters instead of bytes in Result Temp1 := Temp1 + Temp2; Move ( ADelimiter [1], Result [Temp1], DelimiterSize ); Temp1 := Temp1 + DelimiterSize; end; end; procedure TForm1.FormCreate(Sender: TObject); var StrList : TStringList; Str : String; begin // Test 1 : StringListToDelimitedString StrList := TStringList.Create; Str := ''; StrList.Add ( 'Hello1' ); StrList.Add ( 'Hello2' ); StrList.Add ( 'Hello3' ); StrList.Add ( 'Hello4' ); Str := StringListToDelimitedString ( StrList, ';' ); Results.Lines.Add ( Str ); StrList.Free; end; end. Please devise a solution and if possible, some explanation. Alternatives are welcome too.

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• File Formats Supported by UIWebView

  - by Mugunth Kumar

  What are all the file formats supported by UIWebView? In my testing, I found that it supports XLS, DOC, PPT, PDF but not XLSX, and DOCX, RTF. It supports image files like, JPG, PNG, GIF, BMP, not sure about TIFF or Exactly, what all types are supported is not clear... The UIWebView documentation also doesn't state it clearly. Could someone please help?

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• What is the difference between NULL in C++ and null in Java?

  - by Stephano

  I've been trying to figure out why C++ is making me crazy typing NULL. Suddenly it hits me the other day; I've been typing null (lower case) in Java for years. Now suddenly I'm programming in C++ and that little chunk of muscle memory is making me crazy. Wikiperipatetic defines C++ NULL as part of the stddef: A macro that expands to a null pointer constant. It may be defined as ((void*)0), 0 or 0L depending on the compiler and the language. Sun's docs tells me this about Java's "null literal": The null type has one value, the null reference, represented by the literal null, which is formed from ASCII characters. A null literal is always of the null type. So this is all very nice. I know what a null pointer reference is, and thank you for the compiler notes. Now I'm a little fuzzy on the idea of a literal in Java so I read on... A literal is the source code representation of a fixed value; literals are represented directly in your code without requiring computation. There's also a special null literal that can be used as a value for any reference type. null may be assigned to any variable, except variables of primitive types. There's little you can do with a null value beyond testing for its presence. Therefore, null is often used in programs as a marker to indicate that some object is unavailable. Ok, so I think I get it now. In C++ NULL is a macro that, when compiled, defines the null pointer constant. In Java, null is a fixed value that any non-primitive can be assigned too; great for testing in a handy if statement. Java does not have pointers, so I can see why they kept null a simple value rather than anything fancy. But why did java decide to change the all caps NULL to null? Furthermore, am I missing anything here?

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• RIA: Manipulate DOM

  - by stephanos

  I want to display a website embedded in my own site and modify the DOM (e.g. change a button's color/size), similar to what Firebug is capable of. I'm aware of the security issues that arise - my plan is to use this approach to do live website usability testing (A/B style). I'm not limited to any specific RIA framework (yet would prefer Flex) - but it has to work without installing anything (so no AIR). Cheers :-)

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• Is DateTime.ParseExact() faster than DateTime.Parse()

  - by Nassign

  I would like to know if ParseExact is faster than Parse. I think that it should be ParseExact since you already gave the format but I also think all the checking for the Culture info would slow it down. Does microsoft say in any document on performance difference between the two. The format to be used is a generic 'yyyy/MM/dd' format .

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• Exploding by Array of Delimiters

  - by JoeC

  Is there any way to explode() using an array of delimiters? PHP Manual: array explode ( string $delimiter , string $string [, int $limit ] ) Instead of using string $delimiter is there any way to use array $delimiter without affecting performance too much?

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• Fastest way to read every 30th byte of large binary file?

  - by timmerk

  What is the fastest way to read every 30th byte of a large binary file (2-3 GB)? I've read there are performance problems with fseek because of I/O buffers, but I don't want to read 2-3 GB of data into memory before grabbing every 30th byte either.

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• Linq to SQL Compact - Transaction or just SubmitChanges

  - by eWolf

  I'm using Linq to SQL on an SQL Compact database. I have a function where I insert multiple records into the database. I only call SubmitChanges at the end of the function. Would using a transaction (using the TransactionScope class) bring me any more performance or advantages?

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• Package to compare LSA, TFIDF, Cosine metrics and Language Models

  - by gouwsmeister

  Hi, I'm looking for a package (any language, really) that I can use on a corpus of 50 documents to perform interdocument similarity testing in various metrics, like tfidf, okapi, language models, lsa, etc. I want as a result a document similarity matrix, i.e. doc1 is x% similar to doc2, etc... This is for research purposes, not for production. I specifically want the doc similarity matrix as I want to correlate this with human ratings. Thank you in advance!

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• JSON: How do I alert the name of the first node in level 1 in this code snippet?

  - by user143805

  var response = "{\"tree\":[{\"level1\":[{\"node\":{\"id\": 1,\"name\": \"paradox\",\"parent\": 0}}]},{\"level2\":[{\"node\":{\"id\": 2,\"name\": \"lucent\",\"parent\": 1}},{\"node\":{\"id\": 3,\"name\": \"reiso\",\"parent\": 1}}]},{\"level3\":[{\"node\":{\"id\": 4,\"name\": \"pessi\",\"parent\": 3}},{\"node\":{\"id\": 5,\"name\": \"misho\",\"parent\": 2}}]},{\"level4\":[{\"node\":{\"id\": 6,\"name\": \"hema\",\"parent\": 5}},{\"node\":{\"id\": 7,\"name\": \"iiyo\",\"parent\": 4}}]}]}"; var data = eval("(" + response + ")"); This is a dummy json response I am currently testing. Now how do I get the value of "name" in the 1st node of "level1" from the "tree"? Thanks

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• Opera: How do I hide scroll bar? (not there in Firefox and IE8)

  - by erynion

  I'm testing my pages in different browsers. Opera puts a vertical scroll bar on a page. I added an overflow:hidden to the div (after trying Opera), but the scroll bar is still there. How do I get rid of it (you don't need the scroll bar to view the page). Thanks

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• Reasons for Parallel Extensions working slowly

  - by darja

  I am trying to make my calculating application faster by using Parallel Extensions. I am new in it, so I have just replaced the main foreach loop with Parallel.ForEach. But calculating became more slow. What can be common reasons for decreasing performance of parallel extensions? Thanks

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• nokogiri vs hpricot?

  - by roshan

  Which one would you choose? My important attributes are (not in order) Support & Future enhancements Community & general knowledge base (on the Internet) Comprehensive (i.e proven to parse a wide range of *.*ml pages) Performance Memory Footprint (runtime, not the code-base)

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• Is there any better search method instead of string.Contains("keyword") using asp.net?

  - by Mike108

  For example, the users of our app want to search products by entering a keyword of productName. The Products table of the sql server database contains about 10 million records. Is there any better and higher-performance search method implement instead of productName.Contains("keyword") using asp.net C# ?

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