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• A map and set which uses contiguous memory and has a reserve function

  - by edA-qa mort-ora-y

  I use several maps and sets. The lack of contiguous memory, and high number of (de)allocations, is a performance bottleneck. I need a mainly STL-compatbile map and set class which can use a contiguous block of memory for internal objects (or multiple blocks). It also needs to have a reserve function so that I can preallocate for expected sizes. Before I write my own I'd like to check what is available first. Is there something in Boost which does this? Does somebody know of an available implementation elsewhere? Intrusive collection types are not usable here as the same objects need to exist in several collections. As far as I know STL memory pools are per-type, not per instance. These global pools are not efficient with respect to memory locality in mutli-cpu/core processing. Object pools don't work as the types will be shared between instance but their pool should not. In many cases a hash map may be an option in some cases.

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• Remove undesired indexed keywords from Sql Server FTS Index

  - by Scott

  Could anyone tell me if SQL Server 2008 has a way to prevent keywords from being indexed that aren't really relevant to the types of searches that will be performed? For example, we have the IFilters for PDF and Word hooked in and our documents are being indexed properly as far as I can tell. These documents, however, have lots of numeric values in them that people won't really be searching for or bring back meaningful results. These are still being indexed and creating lots of entries in the full text catalog. Basically we are trying to optimize our search engine in any way we can and assumed all these unnecessary entries couldn't be helping performance. I want my catalog to consist of alphabetic keywords only. The current iFilters work better than I would be able to write in the time I have but it just has more than I need. This is an example of some of the terms from sys.dm_fts_index_keywords_by_document that I want out: $1,000, $100, $250, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 129, 13.1, 14, 14.12, 145, 15, 16.2, 16.4, 18, 18.1, 18.2, 18.3, 18.4, 18.5 These are some examples from the same management view that I think are desirable for keeping and searching on: above, accordingly, accounts, add, addition, additional, additive Any help would be greatly appreciated!

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• c# web extracting programming, which libraries, examples samples please

  - by user287745

  I have just started programming and have made a few small applications in C and C#. My understanding is that programming for web and thing related to web is nowadays a very easy task. Please note this is for personnel learning, not for rent a coder or any money making. An application which can run on any Windows platform even Windows 98. The application should start automatically at a scheduled time and do the following. Connect to a site which displays stock prices summary (high low current open). Capture the data (excluding the other things in the site.) And save it to disk (an SQL database) Please note:- Internet connection is assumed to be there always. Do not want to know how to make database schema or database. The stock exchange has no law prohibiting the use of the data provided on its site, but I do not want to mention the name in case I am wrong, but it's for personal private use only. The data of summary of pricing is arranged in a table such that when copied pasted to MS Excel it automatically forms a table. need steps guidance please, examples, lbraries

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• getting proxies of the correct type in nhibernate

  - by Nir

  I have a problem with uninitialized proxies in nhibernate The Domain Model Let's say I have two parallel class hierarchies: Animal, Dog, Cat and AnimalOwner, DogOwner, CatOwner where Dog and Cat both inherit from Animal and DogOwner and CatOwner both inherit from AnimalOwner. AnimalOwner has a reference of type Animal called OwnedAnimal. Here are the classes in the example: public abstract class Animal { // some properties } public class Dog : Animal { // some more properties } public class Cat : Animal { // some more properties } public class AnimalOwner { public virtual Animal OwnedAnimal {get;set;} // more properties... } public class DogOwner : AnimalOwner { // even more properties } public class CatOwner : AnimalOwner { // even more properties } The classes have proper nhibernate mapping, all properties are persistent and everything that can be lazy loaded is lazy loaded. The application business logic only let you to set a Dog in a DogOwner and a Cat in a CatOwner. The Problem I have code like this: public void ProcessDogOwner(DogOwner owner) { Dog dog = (Dog)owner.OwnedAnimal; .... } This method can be called by many diffrent methods, in most cases the dog is already in memory and everything is ok, but rarely the dog isn't already in memory - in this case I get an nhibernate "uninitialized proxy" but the cast throws an exception because nhibernate genrates a proxy for Animal and not for Dog. I understand that this is how nhibernate works, but I need to know the type without loading the object - or, more correctly I need the uninitialized proxy to be a proxy of Cat or Dog and not a proxy of Animal. Constraints I can't change the domain model, the model is handed to me by another department, I tried to get them to change the model and failed. The actual model is much more complicated then the example and the classes have many references between them, using eager loading or adding joins to the queries is out of the question for performance reasons. I have full control of the source code, the hbm mapping and the database schema and I can change them any way I want (as long as I don't change the relationships between the model classes). I have many methods like the one in the example and I don't want to modify all of them. Thanks, Nir

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• Finding a picture in a picture with java?

  - by tarrasch

  what i want to to is analyse input from screen in form of pictures. I want to be able to identify a part of an image in a bigger image and get its coordinates within the bigger picture. Example: would have to be located in And the result would be the upper right corner of the picture in the big picture and the lower left of the part in the big picture. As you can see, the white part of the picture is irrelevant, what i basically need is just the green frame. Is there a library that can do something like this for me? Runtime is not really an issue. What i want to do with this is just generating a few random pixel coordinates and recognize the color in the big picture at that position, to recognize the green box fast later. And how would it decrease performance, if the white box in the middle is transparent? The question has been asked several times on SO as it seems without a single answer. I found i found a solution at http://werner.yellowcouch.org/Papers/subimg/index.html . Unfortunately its in C++ and i do not understand a thing. Would be nice to have a Java implementation on SO.

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• Changing CSS Rules using JavaScript or jQuery

  - by Praveen Kumar

  Initial Research I am aware of using .css() to get and set the CSS rules of a particular element. I have seen a website with this CSS: body, table td, select { font-family: Arial Unicode MS, Arial, sans-serif; font-size: small; } I never liked Arial Unicode as a font. Well, that was my personal feel. So, I would use Chrome's Style Inspector to edit the Arial Unicode MS to Segoe UI or something which I like. Is there anyway, other than using the following to achieve the same? Case I $("body, table td, select").css("font-family", "Segoe UI"); Recursive, performance intensive. Doesn't work when things are loaded on the fly. Case II $('<style>body, table td, select {font-famnily: "Segoe UI";}</style>') .appendTo("head"); Any other better method than this? Creates a lot of <style> tags!

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• Why does adding Crossover to my Genetic Algorithm gives me worse results?

  - by MahlerFive

  I have implemented a Genetic Algorithm to solve the Traveling Salesman Problem (TSP). When I use only mutation, I find better solutions than when I add in crossover. I know that normal crossover methods do not work for TSP, so I implemented both the Ordered Crossover and the PMX Crossover methods, and both suffer from bad results. Here are the other parameters I'm using: Mutation: Single Swap Mutation or Inverted Subsequence Mutation (as described by Tiendil here) with mutation rates tested between 1% and 25%. Selection: Roulette Wheel Selection Fitness function: 1 / distance of tour Population size: Tested 100, 200, 500, I also run the GA 5 times so that I have a variety of starting populations. Stop Condition: 2500 generations With the same dataset of 26 points, I usually get results of about 500-600 distance using purely mutation with high mutation rates. When adding crossover my results are usually in the 800 distance range. The other confusing thing is that I have also implemented a very simple Hill-Climbing algorithm to solve the problem and when I run that 1000 times (faster than running the GA 5 times) I get results around 410-450 distance, and I would expect to get better results using a GA. Any ideas as to why my GA performing worse when I add crossover? And why is it performing much worse than a simple Hill-Climb algorithm which should get stuck on local maxima as it has no way of exploring once it finds a local max?

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• Fetching real time data from excel

  - by Umesh Sharma

  I am seriouly looking for your valuable help first time here. If possible, plese help me. I am developing a VB.NET app in which i read "real time data" from a excel sheet using "Microsoft.Office.Interop.Excel" i.e. excel automation. All cells in excel sheet are fetching stock data from some LOCAL DDE Server like "=XYZ|Bid!GOLD", "=XYZ|Bid!SILVER", "=XYZ|Ask!SILVER" and so on... Some cells also having fixed values like "Symbol", "Bid Rate", "32.90" etc. Values of DDE mapped cells (i.e. =XYZ|xxxx!yyy) are continuously changing. THE PROBLEM is here..."FIXED values" from excel cells are coming quite ok to my app but all DDE mapped cells values are coming "-2146826246" (When datasource local dde server ON) or "-2146826265" (OFF). Although, if i use C#.NET, it's all ok but not with Vb.NET. I want to display range of excel (A1 to J50) into VB.NET ListView which are changing in every 200ms (5 times in every 1 second) ================ Important ====================================================== Is it possible to BIND "listview items/columns values" with "excel cells" or some local memory variables ?? Currently, i am reading excel "cell by cell" and trying to put values in .NET listview but CPU USES are very high as well as it's toooo slow process. If yes, then how please ? I am a VFP developer but new to .NET It's very easy in VFP then why not in .NET ?? Please guide me, if someone has the solution...

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• Avoiding GC thrashing with WSE 3.0 MTOM service

  - by Leon Breedt

  For historical reasons, I have some WSE 3.0 web services that I cannot upgrade to WCF on the server side yet (it is also a substantial amount of work to do so). These web services are being used for file transfers from client to server, using MTOM encoding. This can also not be changed in the short term, for reasons of compatibility. Secondly, they are being called from both Java and .NET, and therefore need to be cross-platform, hence MTOM. How it works is that an "upload" WebMethod is called by the client, sending up a chunk of data at a time, since files being transferred could potentially be gigabytes in size. However, due to not being able to control parts of the stack before the WebMethod is invoked, I cannot control the memory usage patterns of the web service. The problem I am running into is for file sizes from 50MB or so onwards, performance is absolutely killed because of GC, since it appears that WSE 3.0 buffers each chunk received from the client in a new byte[] array, and by the time we've done 50MB we're spending 20-30% of time doing GC. I've played with various chunk sizes, from 16k to 2MB, with no real great difference in results. Smaller chunks are killed by the latency involved with round-tripping, and larger chunks just postpone the slowdown until GC kicks in. Any bright ideas on cutting down on the garbage created by WSE? Can I plug into the pipeline somehow and jury-rig something that has access to the client's request stream and streams it to the WebMethod? I'm aware that it is possible to "stream" responses to the client using WSE (albeit very ugly), but this problem is with requests from the client.

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• deepcopy and python - tips to avoid using it?

  - by blackkettle

  Hi, I have a very simple python routine that involves cycling through a list of roughly 20,000 latitude,longitude coordinates and calculating the distance of each point to a reference point. def compute_nearest_points( lat, lon, nPoints=5 ): """Find the nearest N points, given the input coordinates.""" points = session.query(PointIndex).all() oldNearest = [] newNearest = [] for n in xrange(nPoints): oldNearest.append(PointDistance(None,None,None,99999.0,99999.0)) newNearest.append(obj2) #This is almost certainly an inappropriate use of deepcopy # but how SHOULD I be doing this?!?! for point in points: distance = compute_spherical_law_of_cosines( lat, lon, point.avg_lat, point.avg_lon ) k = 0 for p in oldNearest: if distance < p.distance: newNearest[k] = PointDistance( point.point, point.kana, point.english, point.avg_lat, point.avg_lon, distance=distance ) break else: newNearest[k] = deepcopy(oldNearest[k]) k += 1 for j in range(k,nPoints-1): newNearest[j+1] = deepcopy(oldNearest[j]) oldNearest = deepcopy(newNearest) #We're done, now print the result for point in oldNearest: print point.station, point.english, point.distance return I initially wrote this in C, using the exact same approach, and it works fine there, and is basically instantaneous for nPoints<=100. So I decided to port it to python because I wanted to use SqlAlchemy to do some other stuff. I first ported it without the deepcopy statements that now pepper the method, and this caused the results to be 'odd', or partially incorrect, because some of the points were just getting copied as references(I guess? I think?) -- but it was still pretty nearly as fast as the C version. Now with the deepcopy calls added, the routine does it's job correctly, but it has incurred an extreme performance penalty, and now takes several seconds to do the same job. This seems like a pretty common job, but I'm clearly not doing it the pythonic way. How should I be doing this so that I still get the correct results but don't have to include deepcopy everywhere?

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• Designing secure consumer blackberry application

  - by Kiran Kuppa

  I am evaluating a requirement for a consumer blackberry application that places high premium on security of user's data. Seems like it is an insurance company. Here are my ideas on how I could go about it. I am sure this would be useful for others who are looking for similar stuff Force the user to use device password. (I am guessing that this would be possible - though not checked it yet). Application can request notifications when the device is about to be locked and just after it has been unlocked. Encryption of application specific data can be managed at those times. Application data would be encrypted with user's password. User's credentials would be encrypted with device password. Remote backup of the data could be done over HTTPS (any better ideas are appreciated) Questions: What if the user forgets his device password. If the user forgets his application password, what is the best and secure way to reset the password? If the user losses the phone, remote backup must be done and the application data must be cleaned up. I have some ideas on how to achieve (3) and shall share them. There must be an off-line verification of the user's identity and the administrator must provide a channel using which the user must be able to send command to the device to perform the wiping of application data. The idea is that the user is ALWAYS in control of his data. Without the user's consent, even the admin must not be able to do activities such as cleaning up the data. In the above scheme of things, it appears as if the user's password need not be sent over the air to server. Am I correct? Thanks, --Kiran Kumar

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• How does PHP PDO work internally ?

  - by Rachel

  I want to use pdo in my application, but before that I want to understand how internally PDOStatement->fetch and PDOStatement->fetchAll. For my application, I want to do something like "SELECT * FROM myTable" and insert into csv file and it has around 90000 rows of data. My question is, if I use PDOStatement->fetch as I am using it here: // First, prepare the statement, using placeholders $query = "SELECT * FROM tableName"; $stmt = $this->connection->prepare($query); // Execute the statement $stmt->execute(); var_dump($stmt->fetch(PDO::FETCH_ASSOC)); while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) { echo "Hi"; // Export every row to a file fputcsv($data, $row); } Will after every fetch from database, result for that fetch would be store in memory ? Meaning when I do second fetch, memory would have data of first fetch as well as data for second fetch. And so if I have 90000 rows of data and if am doing fetch every time than memory is being updated to take new fetch result without removing results from previous fetch and so for the last fetch memory would already have 89999 rows of data. Is this how PDOStatement::fetch works ? Performance wise how does this stack up against PDOStatement::fetchAll ?

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• How can I factor out repeated expressions in an SQL Query? Column aliases don't seem to be the ticke

  - by Weston C

  So, I've got a query that looks something like this: SELECT id, DATE_FORMAT(CONVERT_TZ(callTime,'+0:00','-7:00'),'%b %d %Y') as callDate, DATE_FORMAT(CONVERT_TZ(callTime,'+0:00','-7:00'),'%H:%i') as callTimeOfDay, SEC_TO_TIME(callLength) as callLength FROM cs_calldata WHERE customerCode='999999-abc-blahblahblah' AND CONVERT_TZ(callTime,'+0:00','-7:00') >= '2010-04-25' AND CONVERT_TZ(callTime,'+0:00','-7:00') <= '2010-05-25' If you're like me, you probably start thinking that maybe it would improve readability and possibly the performance of this query if I wasn't asking it to compute CONVERT_TZ(callTime,'+0:00','-7:00') four separate times. So I try to create a column alias for that expression and replace further occurances with that alias: SELECT id, CONVERT_TZ(callTime,'+0:00','-7:00') as callTimeZoned, DATE_FORMAT(callTimeZoned,'%b %d %Y') as callDate, DATE_FORMAT(callTimeZoned,'%H:%i') as callTimeOfDay, SEC_TO_TIME(callLength) as callLength FROM cs_calldata WHERE customerCode='5999999-abc-blahblahblah' AND callTimeZoned >= '2010-04-25' AND callTimeZoned <= '2010-05-25' This is when I learned, to quote the MySQL manual: Standard SQL disallows references to column aliases in a WHERE clause. This restriction is imposed because when the WHERE clause is evaluated, the column value may not yet have been determined. So, that approach would seem to be dead in the water. How is someone writing queries with recurring expressions like this supposed to deal with it?

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• How do I process the configure file when cross-compiling with mingw?

  - by vy32

  I have a small open source program that builds with an autoconf configure script. I ran configure I tried to compile with: make CC="/opt/local/bin/i386-mingw32-g++" That didn't work because the configure script found include files that were not available to the mingw system. So then I tried: ./configure CC="/opt/local/bin/i386-mingw32-g++" But that didn't work; the configure script gives me this error: ./configure: line 5209: syntax error near unexpected token `newline' ./configure: line 5209: ` *_cv_*' Because of this code: # The following way of writing the cache mishandles newlines in values, # but we know of no workaround that is simple, portable, and efficient. # So, we kill variables containing newlines. # Ultrix sh set writes to stderr and can't be redirected directly, # and sets the high bit in the cache file unless we assign to the vars. ( for ac_var in `(set) 2>&1 | sed -n 's/^\(a-zA-Z_a-zA-Z0-9_*\)=.*/\1/p'`; do eval ac_val=\$$ac_var case $ac_val in #( *${as_nl}*) case $ac_var in #( *_cv_* fi Which is generated then the AC_OUTPUT is called. Any thoughts? Is there a correct way to do this?

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• C# Execute Method (with Parameters) with ThreadPool

  - by washtik

  We have the following piece of code (idea for this code was found on this website) which will spawn new threads for the method "Do_SomeWork()". This enables us to run the method multiple times asynchronously. The code is: var numThreads = 20; var toProcess = numThreads; var resetEvent = new ManualResetEvent(false); for (var i = 0; i < numThreads; i++) { new Thread(delegate() { Do_SomeWork(Parameter1, Parameter2, Parameter3); if (Interlocked.Decrement(ref toProcess) == 0) resetEvent.Set(); }).Start(); } resetEvent.WaitOne(); However we would like to make use of ThreadPool rather than create our own new threads which can be detrimental to performance. The question is how can we modify the above code to make use of ThreadPool keeping in mind that the method "Do_SomeWork" takes multiple parameters and also has a return type (i.e. method is not void). Also, this is C# 2.0.

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• verilog / systemverilog -- What is the behavior of blocking statements across two always blocks?

  - by miles.sherman

  I am wondering about the behavior of the below code. There are two always blocks, one is combinational to calculate the next_state signal, the other is sequential which will perform some logic and determine whether or not to shutdown the system. It does this by setting the shutdown_now signal high and then calling state <= next_state. My question is if the conditions become true that the shutdown_now signal is set (during clock cycle n) in a blocking manner before the state <= next_state line, will the state during clock cycle n+1 be SHUTDOWN or RUNNING? In other words, does the shutdown_now = 1'b1 line block across both state machines since the state signal is dependent on it through the next_state determination? enum {IDLE, RUNNING, SHUTDOWN} state, next_state; logic shutdown_now; // State machine (combinational) always_comb begin case (state) IDLE: next_state <= RUNNING; RUNNING: next_state <= shutdown ? SHUTDOWN : RUNNING; SHUTDOWN: next_state <= SHUTDOWN; default: next_state <= SHUTDOWN; endcase end // Sequential Behavior always_ff @ (posedge clk) begin // Some code here if (/*some condition) begin shutdown_now = 1'b0; end else begin shutdown_now = 1'b1; end state <= next_state; end

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• Best way to replace mass emails sent from Entourage with a proper mailing list solution?

  - by aaandre

  I am helping a Los Angeles choreographer to transition away from sending her announcements via Entourage. Here's the situation: She has multiple conact groups, and sends classes and performance announcements several times a month, to different groups. She manages the contact groups manually. The group size is between 1500 and 2500 people. Recently verizon blocked her outgoing port 25, presumably for spam activity. Again, her contacts are interested in the content. She is aware of mailchimp, constantcontact etc. but would like to be able to send the email via her email software and not have to create a newsletter for every single mailing. Also, she's very short on $$. So, what would be the best way to set up a system allowing her to send announcements from Entourage, with attached images, to her lists, without having Entourage send every single email? I am thinking of setting up a set of mailing lists, each corresponding to one of her groups. I have never set up a mailing list before and am wondering if it's possible to have a list accept emails from only one person (Admin) and distribute them to the group? Recipients should be able to unsubscribe easily, and by default reply to her but not the list. She should be the only one able to use the list for distribution, and should be able to send messages (with attachments) directly from her email client without modification. Is this possible? Where can I find step-by-step instructions? What are best practices to avoid her domain being blacklisted? What's the easiest way to convert her contact groups to mailing list subscribers? I am helping her for free, so the simpler the better :) Thank you! UPDATE: She has a standard linux hosting account allowing her to run php etc. And, ideally, the emails would come from her personally or at least from her domain name.

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• SQL to get list of dates as well as days before and after without duplicates

  - by Nathan Koop

  I need to display a list of dates, which I have in a table SELECT mydate AS MyDate, 1 AS DateType FROM myTable WHERE myTable.fkId = @MyFkId; Jan 1, 2010 - 1 Jan 2, 2010 - 1 Jan 10, 2010 - 1 No problem. However, I now need to display the date before and the date after as well with a different DateType. Dec 31, 2009 - 2 Jan 1, 2010 - 1 Jan 2, 2010 - 1 Jan 3, 2010 - 2 Jan 9, 2010 - 2 Jan 10, 2010 - 1 Jan 11, 2010 - 2 I thought I could use a union SELECT MyDate, DateType FROM ( SELECT mydate - 1 AS MyDate, 2 AS DateType FROM myTable WHERE myTable.fkId = @MyFkId; UNION SELECT mydate + 1 AS MyDate, 2 AS DateType FROM myTable WHERE myTable.fkId = @MyFkId; UNION SELECT mydate AS MyDate, 1 AS DateType FROM myTable WHERE myTable.fkId = @MyFkId; ) AS myCombinedDateTable This however includes duplicates of the original dates. Dec 31, 2009 - 2 Jan 1, 2009 - 2 Jan 1, 2010 - 1 Jan 2, 2010 - 2 Jan 2, 2010 - 1 Jan 3, 2010 - 2 Jan 9, 2010 - 2 Jan 10, 2010 - 1 Jan 11, 2010 - 2 How can I best remove these duplicates? I am considering a temporary table, but am unsure if that is the best way to do it. This also appears to me that it may provide performance issues as I am running the same query three separate times. What would be the best way to handle this request?

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• MYSQL fetch 10 posts, each w/ vote count, sorted by vote count, limited by where clause on posts

  - by nibblebot

  I want to fetch a set of Posts w/ vote count listed, sorted by vote count (e.g.) Post 1 - Post Body blah blah - Votes: 500 Post 2 - Post Body blah blah - Votes: 400 Post 3 - Post Body blah blah - Votes: 300 Post 4 - Post Body blah blah - Votes: 200 I have 2 tables: Posts - columns - id, body, is_hidden Votes - columns - id, post_id, vote_type_id Here is the query I've tried: SELECT p.*, v.yes_count FROM posts p LEFT JOIN (SELECT post_id, vote_type_id, COUNT(1) AS yes_count FROM votes WHERE (vote_type_id = 1) GROUP BY post_id ORDER BY yes_count DESC LIMIT 0, 10) v ON v.post_id = p.id WHERE (p.is_hidden = 0) ORDER BY yes_count DESC LIMIT 0, 10 Correctness: The above query almost works. The subselect is including votes for posts that have is_hidden = 1, so when I left join it to posts, if a hidden post is in the top 10 (ranked by votes), I can end up with records with NULL on the yes_count field. Performance: I have ~50k posts and ~500k votes. On my dev machine, the above query is running in .4sec. I'd like to stay at or below this execution time. Indexes: I have an index on the Votes table that covers the fields: vote_type_id and post_id EXPLAIN id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY p ALL NULL NULL NULL NULL 45985 Using where; Using temporary; Using filesort 1 PRIMARY <derived2> ALL NULL NULL NULL NULL 10 2 DERIVED votes ref VotingPost VotingPost 4 319881 Using where; Using index; Using temporary; Using filesort

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• Help needed in grokking password hashes and salts

  - by javafueled

  I've read a number of SO questions on this topic, but grokking the applied practice of storing a salted hash of a password eludes me. Let's start with some ground rules: a password, "foobar12" (we are not discussing the strength of the password). a language, Java 1.6 for this discussion a database, postgreSQL, MySQL, SQL Server, Oracle Several options are available to storing the password, but I want to think about one (1): Store the password hashed with random salt in the DB, one column Found on SO and elsewhere is the automatic fail of plaintext, MD5/SHA1, and dual-columns. The latter have pros and cons MD5/SHA1 is simple. MessageDigest in Java provides MD5, SHA1 (through SHA512 in modern implementations, certainly 1.6). Additionally, most RDBMSs listed provide methods for MD5 encryption functions on inserts, updates, etc. The problems become evident once one groks "rainbow tables" and MD5 collisions (and I've grokked these concepts). Dual-column solutions rest on the idea that the salt does not need to be secret (grok it). However, a second column introduces a complexity that might not be a luxury if you have a legacy system with one (1) column for the password and the cost of updating the table and the code could be too high. But it is storing the password hashed with a random salt in single DB column that I need to understand better, with practical application. I like this solution for a couple of reasons: a salt is expected and considers legacy boundaries. Here's where I get lost: if the salt is random and hashed with the password, how can the system ever match the password? I have theory on this, and as I type I might be grokking the concept: Given a random salt of 128 bytes and a password of 8 bytes ('foobar12'), it could be programmatically possible to remove the part of the hash that was the salt, by hashing a random 128 byte salt and getting the substring of the original hash that is the hashed password. Then re hashing to match using the hash algorithm...??? So... any takers on helping. :) Am I close?

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• NSOperation and fwrite (Iphone)

  - by Sridhar

  Hi, I am having problem with this code.Basically I want to execute the fwrite from a timer function asyncronusly. Here is the code block in my Timer function. (This will call by the timer every 0.2 seconds. -(void)timerFunction { WriteFileOperation * operation = [WriteFileOperation writeFileWithBuffer:pFile buffer:readblePixels length:nBytes*15]; [_queue addOperation:operation]; // Here it is waiting to complete the fwrite } The WrtiteFilerOperation is an NSoperation class which it has to write the passing buffer to a file. I added this code in WriteFileOperation's "start" method. (void)start { if (![NSThread isMainThread]) { [self performSelectorOnMainThread:@selector(start) withObject:nil waitUntilDone:NO]; return; } [self willChangeValueForKey:@"isExecuting"]; _isExecuting = YES; [self didChangeValueForKey:@"isExecuting"]; NSLog(@"write bytes %d",fwrite(_buffer, 1, _nBytes, _file)); free(_buffer); [self finish]; } The problem here is , my timerFunction blocked by NSOperation until it writes the buffer into file.(I mean blocked till start method finishes its execution) and the performance seems same as directly placing the fwrite in timerFunction. I want to just return to timerFunction with out waiting from the start method execution to be completed. What I am doing wrong here ? Thanks In Advance Raghu

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• WPF abnormal CPU usage for animation

  - by 0xDEAD BEEF

  HI! I am developing WPF application and client reports extreamly high CPU usage (90%) (whereas i am unable to repeat that behavior). I have traced bootleneck down to these lines. It is simple glowing animation for small single led control (blinking led). What could be reason for this simple annimation taking up SO huge CPU resources? <Trigger Property="State"> <Trigger.Value> <local:BlinkingLedStatus>Blinking</local:BlinkingLedStatus> </Trigger.Value> <Trigger.EnterActions> <BeginStoryboard Name="beginStoryBoard"> <Storyboard> <DoubleAnimation Storyboard.TargetName="glow" Storyboard.TargetProperty="Opacity" AutoReverse="True" From="0.0" To="1.0" Duration="0:0:0.5" RepeatBehavior="Forever"/> </Storyboard> </BeginStoryboard> </Trigger.EnterActions> <Trigger.ExitActions> <StopStoryboard BeginStoryboardName="beginStoryBoard"/> </Trigger.ExitActions> </Trigger>

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• Fastest way to generate delimited string from 1d numpy array

  - by Abiel

  I have a program which needs to turn many large one-dimensional numpy arrays of floats into delimited strings. I am finding this operation quite slow relative to the mathematical operations in my program and am wondering if there is a way to speed it up. For example, consider the following loop, which takes 100,000 random numbers in a numpy array and joins each array into a comma-delimited string. import numpy as np x = np.random.randn(100000) for i in range(100): ",".join(map(str, x)) This loop takes about 20 seconds to complete (total, not each cycle). In contrast, consider that 100 cycles of something like elementwise multiplication (x*x) would take than one 1/10 of a second to complete. Clearly the string join operation creates a large performance bottleneck; in my actual application it will dominate total runtime. This makes me wonder, is there a faster way than ",".join(map(str, x))? Since map() is where almost all the processing time occurs, this comes down to the question of whether there a faster to way convert a very large number of numbers to strings.

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• ANTLR Tree Grammar and StringTemplate Code Translation

  - by Behrooz Nobakht

  I am working on a code translation project with a sample ANTLR tree grammar as: start: ^(PROGRAM declaration+) -> program_decl_tmpl(); declaration: class_decl | interface_decl; class_decl: ^(CLASS ^(ID CLASS_IDENTIFIER)) -> class_decl_tmpl(cid={$CLASS_IDENTIFIER.text}); The group template file for it looks like: group My; program_decl_tmpl() ::= << *WHAT?* >> class_decl_tmpl(cid) ::= << public class <cid> {} >> Based on this, I have these questions: Everything works fine apart from that what I should express in WHAT? to say that a program is simply a list of class declarations to get the final generated output? Is this approach averagely suitable for not so a high-level language? I have also studied ANTLR Code Translation with String Templates, but it seems that this approach takes much advantage of interleaving code in tree grammar. Is it also possible to do it as much as possible just in String Templates?

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• Poor execution plans when using a filter and CONTAINSTABLE in a query

  - by Paul McLoughlin

  We have an interesting problem that I was hoping someone could help to shed some light on. At a high level the problem is as below: The following query executes quickly (1 second): SELECT SA.* FROM cg.SEARCHSERVER_ACTYS AS SA JOIN CONTAINSTABLE(CG.SEARCHSERVER_ACTYS, NOTE, 'reports') AS T1 ON T1.[Key]=SA.UNIQUE_ID but if we add a filter to the query, then it takes approximately 2 minutes to return: SELECT SA.* FROM cg.SEARCHSERVER_ACTYS AS SA JOIN CONTAINSTABLE(CG.SEARCHSERVER_ACTYS, NOTE, 'reports') AS T1 ON T1.[Key]=SA.UNIQUE_ID WHERE SA.CHG_DATE'19 Feb 2010' Looking at the execution plan for the two queries, I can see that in the second case there are two places where there are huge differences between the actual and estimated number of rows, these being: 1) For the FulltextMatch table valued function where the estimate is approx 22,000 rows and the actual is 29 million rows (which are then filtered down to 1670 rows before the join) and 2) For the index seek on the full text index, where the estimate is 1 row and the actual is 13,000 rows As a result of the estimates, the optimiser is choosing to use a nested loops join (since it assumes a small number of rows) hence the plan is inefficient. We can work around the problem by either (a) parameterising the query and adding an OPTION (OPTIMIZE FOR UNKNOWN) to the query or (b) by forcing a HASH JOIN to be used. In both of these cases the query returns in sub 1 second and the estimates appear reasonable. My question really is 'why are the estimates being used in the poorly performing case so wildly inaccurate and what can be done to improve them'? Statistics are up to date on the indexes on the indexed view being used here. Any help greatly appreciated.

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