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• Quick, beginner MASM register question - DX:AX

  - by Francisco P.

  Hello, I am currently studying for an exam I'll have on x86 assembly. I didn't have much luck googling for ":", too common of a punctuation mark :/ IDIV - Signed Integer Division Usage: IDIV src Modifies flags: (AF,CF,OF,PF,SF,ZF undefined) Signed binary division of accumulator by source. If source is a byte value, AX is divided by "src" and the quotient is stored in AL and the remainder in AH. If source is a word value, DX:AX is divided by "src", and the quotient is stored in AL and the remainder in DX. Taken from "Intel Opcodes and Mnemonics" What does DX:AX mean? Thanks a lot for your time :)

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• Java Appengine APPSTATS causing java out of memory error

  - by aloo

  I have several servlets in my java appengine app that do in memory sorting and take on the order of seconds to complete. These complete error free. However, I recently enabled appstats for appengine and started receiving the following error: java.lang.OutOfMemoryError: Java heap space at java.util.Arrays.copyOf(Unknown Source) at java.lang.AbstractStringBuilder.expandCapacity(Unknown Source) at java.lang.AbstractStringBuilder.append(Unknown Source) at java.lang.StringBuilder.append(Unknown Source) at java.lang.StringBuilder.append(Unknown Source) at java.lang.StringBuilder.append(Unknown Source) at com.google.appengine.repackaged.com.google.protobuf.TextFormat$TextGenerator.write(TextFormat.java:344) at com.google.appengine.repackaged.com.google.protobuf.TextFormat$TextGenerator.print(TextFormat.java:332) at com.google.appengine.repackaged.com.google.protobuf.TextFormat.printUnknownFields(TextFormat.java:249) at com.google.appengine.repackaged.com.google.protobuf.TextFormat.print(TextFormat.java:47) at com.google.appengine.repackaged.com.google.protobuf.TextFormat.printToString(TextFormat.java:73) at com.google.appengine.tools.appstats.Recorder.makeSummary(Recorder.java:157) at com.google.appengine.tools.appstats.Recorder.makeSyncCall(Recorder.java:239) at com.google.apphosting.api.ApiProxy.makeSyncCall(ApiProxy.java:98) at com.google.appengine.api.datastore.DatastoreApiHelper.makeSyncCall(DatastoreApiHelper.java:54) at com.google.appengine.api.datastore.PreparedQueryImpl.runQuery(PreparedQueryImpl.java:127) at com.google.appengine.api.datastore.PreparedQueryImpl.asQueryResultList(PreparedQueryImpl.java:81) at org.datanucleus.store.appengine.query.DatastoreQuery.fulfillEntityQuery(DatastoreQuery.java:379) at org.datanucleus.store.appengine.query.DatastoreQuery.executeQuery(DatastoreQuery.java:289) at org.datanucleus.store.appengine.query.DatastoreQuery.performExecute(DatastoreQuery.java:239) at org.datanucleus.store.appengine.query.JDOQLQuery.performExecute(JDOQLQuery.java:89) at org.datanucleus.store.query.Query.executeQuery(Query.java:1489) at org.datanucleus.store.query.Query.executeWithArray(Query.java:1371) at org.datanucleus.jdo.JDOQuery.execute(JDOQuery.java:243) at com.poo.pooserver.dataaccess.DataAccessHelper.getPooStream(DataAccessHelper.java:204) at com.poo.pooserver.GetPooStreamServlet.doPost(GetPooStreamServlet.java:58) at javax.servlet.http.HttpServlet.service(HttpServlet.java:713) at javax.servlet.http.HttpServlet.service(HttpServlet.java:806) at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166) at com.google.appengine.tools.appstats.AppstatsFilter.doFilter(AppstatsFilter.java:92) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)

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• IPC::Open3 Fails Running Under Apache

  - by rjray

  I have a module that uses IPC::Open3 (or IPC::Open2, both exhibit this problem) to call an external binary (bogofilter in this case) and feed it some input via the child-input filehandle, then reads the result from the child-output handle. The code works fine when run in most environments. However, the main use of this module is in a web service that runs under Apache 2.2.6. And under that environment, I get the error: Cannot fdopen STDOUT: Invalid argument This only happens when the code runs under Apache. Previously, the code constructed a horribly complex command, which included a here-document for the input, and ran it with back-ticks. THAT worked, but was very slow and prone to breaking in unique and perplexing ways. I would hate to have to revert to the old version, but I cannot crack this.

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• Get timestamp from Authenticode Signed files in .NET

  - by SlavaGu

  We need to verify that binary files are signed properly with digital signature (Authenticode). This can be achieved with signtool.exe pretty easily. However, we need an automatic way that also verifies signer name and timestamp. This is doable in native C++ with CryptQueryObject() API as shown in this wonderful sample: How To Get Information from Authenticode Signed Executables However we live in a managed world :) hence looking for C# solution to the same problem. Straight approach would be to pInvoke Crypt32.dll and all is done. But there is similar managed API in System.Security.Cryptography.X509Certificates Namespace. X509Certificate2 Class seems to provide some information but no timestamp. Now we came to the original question how can we get that timestamp of a digital signature in C Sharp?

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• Performance: use a BinaryReader on a MemoryStream to read a byte array, or read directly?

  - by Virtlink

  I would like to know whether using a BinaryReader on a MemoryStream created from a byte array (byte[]) would reduce performance significantly. There is binary data I want to read, and I get that data as an array of bytes. I am currently deciding between two approaches to read the data, and have to implement many reading methods accordingly. After each reading action, I need the position right after the read data, and therefor I am considering using a BinaryReader. The first, non-BinaryReader approach: object Read(byte[] data, ref int offset); The second approach: object Read(BinaryReader reader); Such Read() methods will be called very often, in succession on the same data until all data has been read. So, using a BinaryReader feels more natural, but has it much impact on the performance?

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• .gitconfig error

  - by Tanner

  I edited my .gitconfig file to add support for LabView and it appears that I did something that Git doesn't exactly like. The problem is it (Git) doesn't tell me what it doesn't like. What did I do wrong? The error message doesn't help much either: "fatal: bad config file line 13 in c:/Users/Tanner/.gitconfig" [gui] recentrepo = C:/Users/Tanner/Desktop/FIRST 2010 Beta/Java/LoganRover [user] name = Tanner Smith email = [email protected] [merge "labview"] name = LabView 3-Way Merge driver = “C:\Program Files\National Instruments\Shared\LabVIEW Merge\LVMerge.exe” “C:\Program Files\National Instruments\LabVIEW 8.6\LabVIEW.exe” %O %B %A %A recursive = binary And I'm not seeing a line 13, but usually that would mean something is wrong at the end? I don't know, Git is new to me.

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• Looking for calculator source code, BSD-licensed

  - by Horace Ho

  I have an urgent project which need many functions of a calculator (plus a few in-house business rule formulas). As I won't have time to re-invent the wheel so I am looking for source code directly. Requirements: BSD licensed (GPL won't help) in c/c++ programming language 32-bit CPU minimum dependency on platform API/data structure best with both RPN and prefix notation supported emulator/simulator code also acceptable (if not impossible to add custom formula) with following functions (from wikipedia) Scientific notation for calculating large numbers floating point arithmetic logarithmic functions, using both base 10 and base e trigonometry functions (some including hyperbolic trigonometry) exponents and roots beyond the square root quick access to constants such as pi and e plus hexadecimal, binary, and octal calculations, including basic Boolean math fractions optional statistics and probability calculations complex numbers programmability equation solving

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• Python repl in python application

  - by Olorin

  Hello i am learning python(so i can use qt with python not only c++) and i'm curios if it would be possible to embed a python interpreter in my application as a repl. I would like to give users to possibility to script the app using python either loading a file (and that file to act as a plugin for the app) or by evaluating code entered in a text box or something like that. Just like you can embed the interpreter in C or C++ and script the app using python can this be done if the application is itself written in python(and made a stand-alone binary using py2exe or something similar)? something like Anders did with the C# repl or Miguel with mono. Thanks.

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• the carry flag issue!

  - by Zia ur Rahman

  Suppose AX =FFFE and BX=1234 now if we write cmp ax,bx (bx will be subtracted from ax and the approprite flages will be updated) now the binary representation of the numbers in ax and bx is given by AX = 1111 1111 1111 1110 BX= 0001 0010 0011 0100 As bx will be subtracted from ax so we have to negate bx (as Result= ax+(-bx)) so the negated bx (2's complement of bx ) is given by. BX= 1110 1101 1100 1100 Now we add both ax and bx (as subtraction is implemented by addition in computer) AX= 1111 1111 1111 1110 BX= 1110 1101 1100 1100 ------------------------------------ 1 1110 1101 1100 1010 Now as you can see the result is of 17 bits now the 17th bit should go into carry flage, but when i checked it the carry flag is 0 that is CF=0 why?

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• Python serialize lexical closures?

  - by dsimcha

  Is there a way to serialize a lexical closure in Python using the standard library? pickle and marshal appear not to work with lexical closures. I don't really care about the details of binary vs. string serialization, etc., it just has to work. For example: def foo(bar, baz) : def closure(waldo) : return baz * waldo return closure I'd like to just be able to dump instances of closure to a file and read them back. Edit: One relatively obvious way that this could be solved is with some reflection hacks to convert lexical closures into class objects and vice-versa. One could then convert to classes, serialize, unserialize, convert back to closures. Heck, given that Python is duck typed, if you overloaded the function call operator of the class to make it look like a function, you wouldn't even really need to convert it back to a closure and the code using it wouldn't know the difference. If any Python reflection API gurus are out there, please speak up.

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• Size of static libraries generated by XCode

  - by shaft80

  I have a project tree in XCode that looks like this: AppProject depends on ObjcWrapper that in turn depends on PureCppLib. ObjcWrapper and PureCppLib are static library projects. Combined, all sources barely reach 15k lines of code, and, as expected, the size of resulting binary is about 750Kb in release mode and slightly over 1Mb in debug mode. So far, so good. However, ObjcWraper.a and PureCppLib.a are over 6Mb each in either mode. So the first question is why it is so. But more importantly, how can I ensure that those static libs do not include parts or all of the source code? Thanks in advance!

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• teaching my self Z/OS assembler?

  - by Jared

  'I've interned at a company that does a lot of mainframe work. Most of my mainframe experience has been using Java and Unix System Services. I've had some experience with the ISPF interface and C but none with assembler. I’m graduating shortly and will be taking an independent study my last semester. I’d like to stick with the mainframe and was wondering what resources could teach me mainframe assembler? Note I don’t have experience writing assembler for any platform but do understand binary, hex, and have a theoretical understanding of registers.

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• PHPExcel set specific headers for file format

  - by Asif

  Hi, While googling I found two different sets of headers that need to be set when outputting excel generated in different file format. for e.g. For Type "Excel5" headers are: header("Pragma: public"); header("Expires: 0"); header("Cache-Control: must-revalidate, post-check=0, pre-check=0"); header("Content-Type: application/force-download"); header("Content-Type: application/octet-stream"); header("Content-Type: application/download");; header("Content-Disposition: attachment;filename=$filename"); header("Content-Transfer-Encoding: binary "); For Type "Excel2007" headers are: header('Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'); header('Content-Disposition: attachment;filename="myfile.xlsx"'); header('Cache-Control: max-age=0'); My question: is there need to set up different headers for each file type as there are other file types also CSV, HTML and PDF?

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• Studying MySQL, SQLite source code to learn about RDBMS implementation

  - by Yang

  I know implementing database is a huge topic, but I want to have a basic understanding of how database systems work (e.g. memory management, binary tree, transaction, sql parsing, multi-threading, partitions, etc) by investigating the source code of the database. Since there are a few already proven very robust open source databases like mysql, sqlite and so on. However, the code are very complicated and I have no clue where to start. Also I find that the old school database textbooks are only explaining the theory, not the implementation details. Can anyone suggest how I should get started and if there are any books that emphasis on the technology and techniques of building dbms used in modern database industry?

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• LD_LIBRARY_PATH : how to find a shared object

  - by CuriousDawg

  I have a shared object ( libxyz.so ). Given LD_LIBRARY_PATH, how can find the exact location of this shared object? If i had a binary that depends on this lib, i would have used ldd on that. Here is the reason why i ask: I have a cgi script which works when using LD_LIBRARY_PATH set to say VALUE1. It does not work when the path is set to VALUE2. I would like to find the exact location of the library as specified by the path in VALUE1 ( Note that VALUE1 has almost 20+ different locations ) Platform: Linux

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• Books and resources for Java Performance tuning - when working with databases, huge lists

  - by Arvind

  Hi All, I am relatively new to working on huge applications in Java. I am working on a Java web service which is pretty heavily used by various clients. The service basically queries the database (hibernate) and then works with a lot of Lists (there are adapters to convert list returned from DB to the interface which the service publishes) and I am seeing lot of issues with the service like high CPU usage or high heap space. While I can troubleshoot the performance issues using a profiler, I want to actually learn about what all I need to take care when I actually write code. Like what kind of List to use or things like using StringBuilder instead of String, etc... Is there any book or blogs which I can refer which will help me while I write new services? Also my application is multithreaded - each service call from a client is a new thread, and I want to know some best practices around that area as well. I did search the web but I found many tips which are not relevant in the latest Java 6 releases, so wanted to know what kind of resources would help a developer starting out now on Java for heavily used applications. Arvind

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• "Symbol not found" error for UIPopoverController in an iPhone/iPad Universal App

  - by alexbw

  In a universal binary iPhone/iPad app of mine, users are able to adjust preferences in a view controller that's presented modally. On the iPhone, the settings panel is presented with presentModalViewController:animated:, and on the iPad, I use a UIPopoverController. I'm having a heck of a time completely isolating the UIPopoverController code away from the iPhone code. Everytime I compile for the iPhone, I get the following error: dyld: Symbol not found: _OBJC_CLASS_$_UIPopoverController Referenced from: /var/mobile/Applications/CBB37F87-AA6D-47E2-823A-E259E3268A32/MyApp debug.app/MyApp Expected in: /System/Library/Frameworks/UIKit.framework/UIKit This is of course because UIKit on the iPhone doesn't have a UIPopoverController class. Does anybody have advice for how to effectively isolate the iPad API includes from the iPhone code, so I can actually run my code?

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• Using Hibernate's ScrollableResults to slowly read 90 million records

  - by at

  I simply need to read each row in a table in my MySQL database using Hibernate and write a file based on it. But there are 90 million rows and they are pretty big. So it seemed like the following would be appropriate: ScrollableResults results = session.createQuery("SELECT person FROM Person person") .setReadOnly(true).setCacheable(false).scroll(ScrollMode.FORWARD_ONLY); while (results.next()) storeInFile(results.get()[0]); The problem is the above will try and load all 90 million rows into RAM before moving on to the while loop... and that will kill my memory with OutOfMemoryError: Java heap space exceptions :(. So I guess ScrollableResults isn't what I was looking for? What is the proper way to handle this? I don't mind if this while loop takes days (well I'd love it to not). I guess the only other way to handle this is to use setFirstResult and setMaxResults to iterate through the results and just use regular Hibernate results instead of ScrollableResults. That feels like it will be inefficient though and will start taking a ridiculously long time when I'm calling setFirstResult on the 89 millionth row... UPDATE: setFirstResult/setMaxResults doesn't work, it turns out to take an unusably long time to get to the offsets like I feared. There must be a solution here! Isn't this a pretty standard procedure?? I'm willing to forgo Hibernate and use JDBC or whatever it takes. UPDATE 2: the solution I've come up with which works ok, not great, is basically of the form: select * from person where id > <offset> and <other_conditions> limit 1 Since I have other conditions, even all in an index, it's still not as fast as I'd like it to be... so still open for other suggestions..

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• Looking for a lock-free RT-safe single-reader single-writer structure

  - by moala

  Hi, I'm looking for a lock-free design conforming to these requisites: a single writer writes into a structure and a single reader reads from this structure (this structure exists already and is safe for simultaneous read/write) but at some time, the structure needs to be changed by the writer, which then initialises, switches and writes into a new structure (of the same type but with new content) and at the next time the reader reads, it switches to this new structure (if the writer multiply switches to a new lock-free structure, the reader discards these structures, ignoring their data). The structures must be reused, i.e. no heap memory allocation/free is allowed during write/read/switch operation, for RT purposes. I have currently implemented a ringbuffer containing multiple instances of these structures; but this implementation suffers from the fact that when the writer has used all the structures present in the ringbuffer, there is no more place to change from structure... But the rest of the ringbuffer contains some data which don't have to be read by the reader but can't be re-used by the writer. As a consequence, the ringbuffer does not fit this purpose. Any idea (name or pseudo-implementation) of a lock-free design? Thanks for having considered this problem.

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• What are some Java memory management best practices?

  - by Ascalonian

  I am taking over some applications from a previous developer. When I run the applications through Eclipse, I see the memory usage and the heap size increase a lot. Upon further investigation, I see that they were creating an object over-and-over in a loop as well as other things. I started to go through and do some clean up. But the more I went through, the more questions I had like "will this actually do anything?" For example, instead of declaring a variable outside the loop mentioned above and just setting its value in the loop... they created the object in the loop. What I mean is: for(int i=0; i < arrayOfStuff.size(); i++) { String something = (String) arrayOfStuff.get(i); ... } versus String something = null; for(int i=0; i < arrayOfStuff.size(); i++) { something = (String) arrayOfStuff.get(i); } Am I incorrect to say that the bottom loop is better? Perhaps I am wrong. Also, what about after the second loop above, I set "something" back to null? Would that clear out some memory? In either case, what are some good memory management best practices I could follow that will help keep my memory usage low in my applications? Update: I appreciate everyones feedback so far. However, I was not really asking about the above loops (although by your advice I did go back to the first loop). I am trying to get some best practices that I can keep an eye out for. Something on the lines of "when you are done using a Collection, clear it out". I just really need to make sure not as much memory is being taken up by these applications.

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• undefined symbol: PyUnicodeUCS2_Decode whilst trying to install psycopg2

  - by Marco Fucci

  I'm getting an error whilst trying to install psycopg2 on ubuntu 9.10 64 bit. The error is: >>> import psycopg2 Traceback (most recent call last): File "<stdin>", line 1, in <module> File "psycopg2/__init__.py", line 69, in <module> from _psycopg import BINARY, NUMBER, STRING, DATETIME, ROWID ImportError: psycopg2/_psycopg.so: undefined symbol: PyUnicodeUCS2_Decode I've tried downloading the package from http://initd.org/pub/software/psycopg/ and installing it. I've tried by using easy_install too. No error during the installation. It's quite weird as my python (2.6.2) has been compiled with UCS4 and so the installation should just work without problems. Any help would be appreciated. Cheers

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• retrieve cobol s9(2) COMP onto C variable

  - by Pablo Cazallas

  Hi, I need to retrieve data from a COBOL variable of the type: "PIC S9(2) COMP" onto a C variable of the type "int". It's stored using two bytes of a string, so I receive it as a couple of chars. I know COBOL stores decimal data onto a "S9(2) COMP" in binary format, so It would be a great help letting me know any algorithm or way to convert it safely. Any kind of help & suggestion will be welcome. Thanks in advance and regards, Pablo.

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• To store images in SQL or not?

  - by Brett

  Generally, I had thought it was always better to store images in the filesystem and link to it via the database entry. However, I am trying to optimize my db design and am having a few questions. My images are all really small thumbmails in black and white (not greyscale, but true B&W) and are 70x70 in size. If we take the images (which is basically a 2D array of 1 and 0), it can be stored as binary data that would be approximately 600 bytes each. So my question is whether querying the 600 bytes stored in a db would be faster than querying a link followed by accessing the filesystem; assuming there are a lot of "image" queries being made. Does anyone have any experience with this area? If it matters, I am using MySQL, and MonetDB (separately, but have the same question for both). Many thanks, Brett

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• Dynamically evaluating simple boolean logic in Python

  - by a paid nerd

  I've got some dynamically-generated boolean logic expressions, like: (A or B) and (C or D) A or (A and B) A empty - evaluates to True The placeholders get replaced with booleans. Should I, Convert this information to a Python expression like True or (True or False) and eval it? Create a binary tree where a node is either a bool or Conjunction/Disjunction object and recursively evaluate it? Convert it into nested S-expressions and use a Lisp parser? Something else? Suggestions welcome.

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• Effective thread Synchronization in C#

  - by n0vic3c0d3r

  I have a scenario where I need to search from many binary files (using keys) and combine the results (strings). Until now, I have been doing it in a for loop one file after the other. foreach (string file in FileSources.Keys) { aggregatedDefinitions.Append(DefinitionLookup(txtSearchWord.Text, file)); } Since this operation is very slow, I was thinking of using threads, so that I could do IO operations in parallel. Is threading the right way to go. If I use threading, how can I ensure that I get the results in the order I want. I haven't used Threading until now. It would be very helpful if you could suggest some materials/books that would help me solve my problem.

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