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  • What are all the concurrent things [data structure, algorithm, locking mechanism] missing in .Net 3.

    - by user49767
    First time I am bit disappointed in StackOverflow cause my http://stackoverflow.com/questions/2571727/c-concurrency-vs-java-concurrency-which-is-neatly-designed-which-is-better question was closed. My intension was just trying to gather knowledge from programming guru's who worked in both the programming technologies. Rather closing this question, please help me by discussing what is good, bad, and ugly in multi-threading part in both the platforms. It is also welcome, if someone would like to compare with .Net 4.0 with JDK 6 (or JDK 7)

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  • A very interesting MYSQL problem (related to indexing, million records, algorithm.)

    - by terence410
    This problem is pretty hard to describe and therefore difficult to search the answer. I hope some expert could share you opinions on that. I have a table with around 1 million of records. The table structure is similar to something like this: items{ uid (primary key, bigint, 15) updated (indexed, int, 11) enabled (indexed, tinyint, 1) } The scenario is like this. I have to select all of the records everyday and do some processing. It takes around 3 second to handle each item. I have written a PHP script to fetch 200 items each time using the following. select * from items where updated unix_timestamp(now()) - 86400 and enabled = 1 limit 200; I will then update the "updated" field of the selected items to make sure that it wont' be selected again within one day. The selected query is something like that. update items set updated = unix_timestamp(now()) where uid in (1,2,3,4,...); Then, the PHP will continue to run and process the data which doesn't require any MYSQL connection anymore. Since I have million records and each record take 3 seconds to process, it's definitely impossible to do it sequentially. Therefore, I will execute the PHP in every 10 seconds. However, as time goes by and the table growth, the select getting much slower. Sometimes, it take more than 100 seconds to run! Do you guys have any suggestion how may I solve this problem?

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  • What's the fastest lookup algorithm for a key, pair data structure (i.e, a map)?

    - by truncheon
    In the following example a std::map structure is filled with 26 values from A - Z (for key) and 0 – 26 for value. The time taken (on my system) to lookup the last entry (10000000 times) is roughly 250 ms for the vector, and 125 ms for the map. (I compiled using release mode, with O3 option turned on for g++ 4.4) But if for some odd reason I wanted better performance than the std::map, what data structures and functions would I need to consider using? I apologize if the answer seems obvious to you, but I haven't had much experience in the performance critical aspects of C++ programming. #include <ctime> #include <map> #include <vector> #include <iostream> struct mystruct { char key; int value; mystruct(char k = 0, int v = 0) : key(k), value(v) { } }; int find(const std::vector<mystruct>& ref, char key) { for (std::vector<mystruct>::const_iterator i = ref.begin(); i != ref.end(); ++i) if (i->key == key) return i->value; return -1; } int main() { std::map<char, int> mymap; std::vector<mystruct> myvec; for (int i = 'a'; i < 'a' + 26; ++i) { mymap[i] = i - 'a'; myvec.push_back(mystruct(i, i - 'a')); } int pre = clock(); for (int i = 0; i < 10000000; ++i) { find(myvec, 'z'); } std::cout << "linear scan: milli " << clock() - pre << "\n"; pre = clock(); for (int i = 0; i < 10000000; ++i) { mymap['z']; } std::cout << "map scan: milli " << clock() - pre << "\n"; return 0; }

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  • Apriori Algorithm- what to do with small min.support?

    - by user3707650
    I have a question about the table beneath my question: If i was told that the given min.support=10%, how can i know what is the support count, by which i will use during the exercise? What i know is: that you take the number of transactions (8) and multiple it by the min.support: 8*(10/100)=0.8 the problem is that i get this number: 0.8, how can i use this support count during this example?? 0.8 is a number that will make me prune all combination set that i will build... please help me!!! TID A B C D E F G 10 1 0 1 0 0 0 1 20 1 1 1 1 0 1 1 30 0 0 0 0 0 0 1 40 0 0 1 0 0 1 1 50 0 0 0 1 1 0 0 60 0 1 1 0 1 1 0 70 0 0 0 0 1 1 0 80 0 0 1 0 1 1 1

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  • Which of these algorithms is best for my goal?

    - by JonathonG
    I have created a program that restricts the mouse to a certain region based on a black/white bitmap. The program is 100% functional as-is, but uses an inaccurate, albeit fast, algorithm for repositioning the mouse when it strays outside the area. Currently, when the mouse moves outside the area, basically what happens is this: A line is drawn between a pre-defined static point inside the region and the mouse's new position. The point where that line intersects the edge of the allowed area is found. The mouse is moved to that point. This works, but only works perfectly for a perfect circle with the pre-defined point set in the exact center. Unfortunately, this will never be the case. The application will be used with a variety of rectangles and irregular, amorphous shapes. On such shapes, the point where the line drawn intersects the edge will usually not be the closest point on the shape to the mouse. I need to create a new algorithm that finds the closest point to the mouse's new position on the edge of the allowed area. I have several ideas about this, but I am not sure of their validity, in that they may have far too much overhead. While I am not asking for code, it might help to know that I am using Objective C / Cocoa, developing for OS X, as I feel the language being used might affect the efficiency of potential methods. My ideas are: Using a bit of trigonometry to project lines would work, but that would require some kind of intense algorithm to test every point on every line until it found the edge of the region... That seems too resource intensive since there could be something like 200 lines that would have each have to have as many as 200 pixels checked for black/white.... Using something like an A* pathing algorithm to find the shortest path to a black pixel; however, A* seems resource intensive, even though I could probably restrict it to only checking roughly in one direction. It also seems like it will take more time and effort than I have available to spend on this small portion of the much larger project I am working on, correct me if I am wrong and it would not be a significant amount of code (100 lines or around there). Mapping the border of the region before the application begins running the event tap loop. I think I could accomplish this by using my current line-based algorithm to find an edge point and then initiating an algorithm that checks all 8 pixels around that pixel, finds the next border pixel in one direction, and continues to do this until it comes back to the starting pixel. I could then store that data in an array to be used for the entire duration of the program, and have the mouse re-positioning method check the array for the closest pixel on the border to the mouse target position. That last method would presumably execute it's initial border mapping fairly quickly. (It would only have to map between 2,000 and 8,000 pixels, which means 8,000 to 64,000 checked, and I could even permanently store the data to make launching faster.) However, I am uncertain as to how much overhead it would take to scan through that array for the shortest distance for every single mouse move event... I suppose there could be a shortcut to restrict the number of elements in the array that will be checked to a variable number starting with the intersecting point on the line (from my original algorithm), and raise/lower that number to experiment with the overhead/accuracy tradeoff. Please let me know if I am over thinking this and there is an easier way that will work just fine, or which of these methods would be able to execute something like 30 times per second to keep mouse movement smooth, or if you have a better/faster method. I've posted relevant parts of my code below for reference, and included an example of what the area might look like. (I check for color value against a loaded bitmap that is black/white.) // // This part of my code runs every single time the mouse moves. // CGPoint point = CGEventGetLocation(event); float tX = point.x; float tY = point.y; if( is_in_area(tX,tY, mouse_mask)){ // target is inside O.K. area, do nothing }else{ CGPoint target; //point inside restricted region: float iX = 600; // inside x float iY = 500; // inside y // delta to midpoint between iX,iY and tX,tY float dX; float dY; float accuracy = .5; //accuracy to loop until reached do { dX = (tX-iX)/2; dY = (tY-iY)/2; if(is_in_area((tX-dX),(tY-dY),mouse_mask)){ iX += dX; iY += dY; } else { tX -= dX; tY -= dY; } } while (abs(dX)>accuracy || abs(dY)>accuracy); target = CGPointMake(roundf(tX), roundf(tY)); CGDisplayMoveCursorToPoint(CGMainDisplayID(),target); } Here is "is_in_area(int x, int y)" : bool is_in_area(NSInteger x, NSInteger y, NSBitmapImageRep *mouse_mask){ NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; NSUInteger pixel[4]; [mouse_mask getPixel:pixel atX:x y:y]; if(pixel[0]!= 0){ [pool release]; return false; } [pool release]; return true; }

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  • How to optimize paging for large in memory database

    - by snakefoot
    I have an application where the entire database is implemented in memory using a stl-map for each table in the database. Each item in the stl-map is a complex object with references to other items in the other stl-maps. The application works with a large amount of data, so it uses more than 500 MByte RAM. Clients are able to contact the application and get a filtered version of the entire database. This is done by running through the entire database, and finding items relevant for the client. When the application have been running for an hour or so, then Windows 2003 SP2 starts to page out parts of the RAM for the application (Eventhough there is 16 GByte RAM on the machine). After the application have been partly paged out then a client logon takes a long time (10 mins) because it now generates a page fault for each pointer lookup in the stl-map. I can see it is possible to tell Windows to lock memory in RAM, but this is generally only recommended for device drivers, and only for "small" amounts of memory. I guess a poor mans solution could be to loop through the entire memory database, and thus tell Windows we are still interested in keeping the datamodel in RAM. I guess another poor mans solution could be to disable the pagefile completely on Windows. I guess the expensive solution would be a SQL database, and then rewrite the entire application to use a database layer. Then hopefully the database system will have implemented means to for fast access. Are there other more elegant solutions ?

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  • ANN for decompiler?

    - by Rhythmic Algorithm
    Has there ever been any attempts at utilizing artificial neural networks in decompilation? It would be nice if it was possible to provide the trimmed semantics of source along with the code in to a neural network so it could learn the connection between the two. I assume this would likely lose it's effectiveness when there is optimizations and maybe work better for high level languages too but I'm interested in hearing any attempts anyone has had at this.

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  • Google street view URL question:

    - by Rhythmic Algorithm
    Hi I have the address of a property and my application can launch a browser to go to http://maps.google.com?q=searchStringHere. If a good match is found it will take it directly there. Is there any thing I can append to the url to make it switch to streetview without having the exact coordinates? I dont't want to code any javascript or flash.

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  • Change save to file name but from the client

    - by Rhythmic Algorithm
    This question asks about file name the servers sends and the fix was quite simply a content-disposition header in the http response. What I interested in is does anyone know of any way to do this from the client side if the file name is already known? Is there any special javascript to do this for example? A site I have to use but not mine has a FileDownload.aspx but it doesn't send the content-disposition header. I know the filename and would like to be able to create a firefox extensions to use for the poorly coded web site. Thanks

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  • C++ .NET DLL vs C# Managed Code ? (File Encrypting AES-128+XTS)

    - by Ranhiru
    I need to create a Windows Mobile Application (WinMo 6.x - C#) which is used to encrypt/decrypt files. However it is my duty to write the encryption algorithm which is AES-128 along with XTS as the mode of operation. RijndaelManaged just doesn't cut it :( Very much slower than DES and 3DES CryptoServiceProviders :O I know it all depends on how good I am at writing the algorithm in the most efficient way. (And yes I my self have to write it from scratch but i can take a look @ other implementations) Nevertheless, does writing a C++ .NET DLL to create the encryption/decryption algorithm + all the file handling and using it from C# have a significant performance advantage OVER writing the encryption algorithm + file handling in completely managed C# code? If I use C++ .NET to create the encryption algorithm, should I use MFC Smart Device DLL or ATL? What is the difference and is there any impact on which one I choose? And can i just add a reference to the C++ DLL from C# or should I use P/Invoke? I am fairly competent with C# than C++ but performance plays a major role as I have convinced my lecturers that AES is a very efficient cryptographic algorithm for resource constrained devices. Thanx a bunch :)

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  • while(true) and loop-breaking - anti-pattern?

    - by KeithS
    Consider the following code: public void doSomething(int input) { while(true) { TransformInSomeWay(input); if(ProcessingComplete(input)) break; DoSomethingElseTo(input); } } Assume that this process involves a finite but input-dependent number of steps; the loop is designed to terminate on its own as a result of the algorithm, and is not designed to run indefinitely (until cancelled by an outside event). Because the test to see if the loop should end is in the middle of a logical set of steps, the while loop itself currently doesn't check anything meaningful; the check is instead performed at the "proper" place within the conceptual algorithm. I was told that this is bad code, because it is more bug-prone due to the ending condition not being checked by the loop structure. It's more difficult to figure out how you'd exit the loop, and could invite bugs as the breaking condition might be bypassed or omitted accidentally given future changes. Now, the code could be structured as follows: public void doSomething(int input) { TransformInSomeWay(input); while(!ProcessingComplete(input)) { DoSomethingElseTo(input); TransformInSomeWay(input); } } However, this duplicates a call to a method in code, violating DRY; if TransformInSomeWay were later replaced with some other method, both calls would have to be found and changed (and the fact that there are two may be less obvious in a more complex piece of code). You could also write it like: public void doSomething(int input) { var complete = false; while(!complete) { TransformInSomeWay(input); complete = ProcessingComplete(input); if(!complete) { DoSomethingElseTo(input); } } } ... but you now have a variable whose only purpose is to shift the condition-checking to the loop structure, and also has to be checked multiple times to provide the same behavior as the original logic. For my part, I say that given the algorithm this code implements in the real world, the original code is the most readable. If you were going through it yourself, this is the way you'd think about it, and so it would be intuitive to people familiar with the algorithm. So, which is "better"? is it better to give the responsibility of condition checking to the while loop by structuring the logic around the loop? Or is it better to structure the logic in a "natural" way as indicated by requirements or a conceptual description of the algorithm, even though that may mean bypassing the loop's built-in capabilities?

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  • Elfsign Object Signing on Solaris

    - by danx
    Elfsign Object Signing on Solaris Don't let this happen to you—use elfsign! Solaris elfsign(1) is a command that signs and verifies ELF format executables. That includes not just executable programs (such as ls or cp), but other ELF format files including libraries (such as libnvpair.so) and kernel modules (such as autofs). Elfsign has been available since Solaris 10 and ELF format files distributed with Solaris, since Solaris 10, are signed by either Sun Microsystems or its successor, Oracle Corporation. When an ELF file is signed, elfsign adds a new section the ELF file, .SUNW_signature, that contains a RSA public key signature and other information about the signer. That is, the algorithm used, algorithm OID, signer CN/OU, and time stamp. The signature section can later be verified by elfsign or other software by matching the signature in the file agains the ELF file contents (excluding the signature). ELF executable files may also be signed by a 3rd-party or by the customer. This is useful for verifying the origin and authenticity of executable files installed on a system. The 3rd-party or customer public key certificate should be installed in /etc/certs/ to allow verification by elfsign. For currently-released versions of Solaris, only cryptographic framework plugin libraries are verified by Solaris. However, all ELF files may be verified by the elfsign command at any time. Elfsign Algorithms Elfsign signatures are created by taking a digest of the ELF section contents, then signing the digest with RSA. To verify, one takes a digest of ELF file and compares with the expected digest that's computed from the signature and RSA public key. Originally elfsign took a MD5 digest of a SHA-1 digest of the ELF file sections, then signed the resulting digest with RSA. In Solaris 11.1 then Solaris 11.1 SRU 7 (5/2013), the elfsign crypto algorithms available have been expanded to keep up with evolving cryptography. The following table shows the available elfsign algorithms: Elfsign Algorithm Solaris Release Comments elfsign sign -F rsa_md5_sha1   S10, S11.0, S11.1 Default for S10. Not recommended* elfsign sign -F rsa_sha1 S11.1 Default for S11.1. Not recommended elfsign sign -F rsa_sha256 S11.1 patch SRU7+   Recommended ___ *Most or all CAs do not accept MD5 CSRs and do not issue MD5 certs due to MD5 hash collision problems. RSA Key Length. I recommend using RSA-2048 key length with elfsign is RSA-2048 as the best balance between a long expected "life time", interoperability, and performance. RSA-2048 keys have an expected lifetime through 2030 (and probably beyond). For details, see Recommendation for Key Management: Part 1: General, NIST Publication SP 800-57 part 1 (rev. 3, 7/2012, PDF), tables 2 and 4 (pp. 64, 67). Step 1: create or obtain a key and cert The first step in using elfsign is to obtain a key and cert from a public Certificate Authority (CA), or create your own self-signed key and cert. I'll briefly explain both methods. Obtaining a Certificate from a CA To obtain a cert from a CA, such as Verisign, Thawte, or Go Daddy (to name a few random examples), you create a private key and a Certificate Signing Request (CSR) file and send it to the CA, following the instructions of the CA on their website. They send back a signed public key certificate. The public key cert, along with the private key you created is used by elfsign to sign an ELF file. The public key cert is distributed with the software and is used by elfsign to verify elfsign signatures in ELF files. You need to request a RSA "Class 3 public key certificate", which is used for servers and software signing. Elfsign uses RSA and we recommend RSA-2048 keys. The private key and CSR can be generated with openssl(1) or pktool(1) on Solaris. Here's a simple example that uses pktool to generate a private RSA_2048 key and a CSR for sending to a CA: $ pktool gencsr keystore=file format=pem outcsr=MYCSR.p10 \ subject="CN=canineswworks.com,OU=Canine SW object signing" \ outkey=MYPRIVATEKEY.key $ openssl rsa -noout -text -in MYPRIVATEKEY.key Private-Key: (2048 bit) modulus: 00:d2:ef:42:f2:0b:8c:96:9f:45:32:fc:fe:54:94: . . . [omitted for brevity] . . . c9:c7 publicExponent: 65537 (0x10001) privateExponent: 26:14:fc:49:26:bc:a3:14:ee:31:5e:6b:ac:69:83: . . . [omitted for brevity] . . . 81 prime1: 00:f6:b7:52:73:bc:26:57:26:c8:11:eb:6c:dc:cb: . . . [omitted for brevity] . . . bc:91:d0:40:d6:9d:ac:b5:69 prime2: 00:da:df:3f:56:b2:18:46:e1:89:5b:6c:f1:1a:41: . . . [omitted for brevity] . . . f3:b7:48:de:c3:d9:ce:af:af exponent1: 00:b9:a2:00:11:02:ed:9a:3f:9c:e4:16:ce:c7:67: . . . [omitted for brevity] . . . 55:50:25:70:d3:ca:b9:ab:99 exponent2: 00:c8:fc:f5:57:11:98:85:8e:9a:ea:1f:f2:8f:df: . . . [omitted for brevity] . . . 23:57:0e:4d:b2:a0:12:d2:f5 coefficient: 2f:60:21:cd:dc:52:76:67:1a:d8:75:3e:7f:b0:64: . . . [omitted for brevity] . . . 06:94:56:d8:9d:5c:8e:9b $ openssl req -noout -text -in MYCSR.p10 Certificate Request: Data: Version: 2 (0x2) Subject: OU=Canine SW object signing, CN=canineswworks.com Subject Public Key Info: Public Key Algorithm: rsaEncryption Public-Key: (2048 bit) Modulus: 00:d2:ef:42:f2:0b:8c:96:9f:45:32:fc:fe:54:94: . . . [omitted for brevity] . . . c9:c7 Exponent: 65537 (0x10001) Attributes: Signature Algorithm: sha1WithRSAEncryption b3:e8:30:5b:88:37:68:1c:26:6b:45:af:5e:de:ea:60:87:ea: . . . [omitted for brevity] . . . 06:f9:ed:b4 Secure storage of RSA private key. The private key needs to be protected if the key signing is used for production (as opposed to just testing). That is, protect the key to protect against unauthorized signatures by others. One method is to use a PIN-protected PKCS#11 keystore. The private key you generate should be stored in a secure manner, such as in a PKCS#11 keystore using pktool(1). Otherwise others can sign your signature. Other secure key storage mechanisms include a SCA-6000 crypto card, a USB thumb drive stored in a locked area, a dedicated server with restricted access, Oracle Key Manager (OKM), or some combination of these. I also recommend secure backup of the private key. Here's an example of generating a private key protected in the PKCS#11 keystore, and a CSR. $ pktool setpin # use if PIN not set yet Enter token passphrase: changeme Create new passphrase: Re-enter new passphrase: Passphrase changed. $ pktool gencsr keystore=pkcs11 label=MYPRIVATEKEY \ format=pem outcsr=MYCSR.p10 \ subject="CN=canineswworks.com,OU=Canine SW object signing" $ pktool list keystore=pkcs11 Enter PIN for Sun Software PKCS#11 softtoken: Found 1 asymmetric public keys. Key #1 - RSA public key: MYPRIVATEKEY Here's another example that uses openssl instead of pktool to generate a private key and CSR: $ openssl genrsa -out cert.key 2048 $ openssl req -new -key cert.key -out MYCSR.p10 Self-Signed Cert You can use openssl or pktool to create a private key and a self-signed public key certificate. A self-signed cert is useful for development, testing, and internal use. The private key created should be stored in a secure manner, as mentioned above. The following example creates a private key, MYSELFSIGNED.key, and a public key cert, MYSELFSIGNED.pem, using pktool and displays the contents with the openssl command. $ pktool gencert keystore=file format=pem serial=0xD06F00D lifetime=20-year \ keytype=rsa hash=sha256 outcert=MYSELFSIGNED.pem outkey=MYSELFSIGNED.key \ subject="O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com" $ pktool list keystore=file objtype=cert infile=MYSELFSIGNED.pem Found 1 certificates. 1. (X.509 certificate) Filename: MYSELFSIGNED.pem ID: c8:24:59:08:2b:ae:6e:5c:bc:26:bd:ef:0a:9c:54:de:dd:0f:60:46 Subject: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com Issuer: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com Not Before: Oct 17 23:18:00 2013 GMT Not After: Oct 12 23:18:00 2033 GMT Serial: 0xD06F00D0 Signature Algorithm: sha256WithRSAEncryption $ openssl x509 -noout -text -in MYSELFSIGNED.pem Certificate: Data: Version: 3 (0x2) Serial Number: 3496935632 (0xd06f00d0) Signature Algorithm: sha256WithRSAEncryption Issuer: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com Validity Not Before: Oct 17 23:18:00 2013 GMT Not After : Oct 12 23:18:00 2033 GMT Subject: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com Subject Public Key Info: Public Key Algorithm: rsaEncryption Public-Key: (2048 bit) Modulus: 00:bb:e8:11:21:d9:4b:88:53:8b:6c:5a:7a:38:8b: . . . [omitted for brevity] . . . bf:77 Exponent: 65537 (0x10001) Signature Algorithm: sha256WithRSAEncryption 9e:39:fe:c8:44:5c:87:2c:8f:f4:24:f6:0c:9a:2f:64:84:d1: . . . [omitted for brevity] . . . 5f:78:8e:e8 $ openssl rsa -noout -text -in MYSELFSIGNED.key Private-Key: (2048 bit) modulus: 00:bb:e8:11:21:d9:4b:88:53:8b:6c:5a:7a:38:8b: . . . [omitted for brevity] . . . bf:77 publicExponent: 65537 (0x10001) privateExponent: 0a:06:0f:23:e7:1b:88:62:2c:85:d3:2d:c1:e6:6e: . . . [omitted for brevity] . . . 9c:e1:e0:0a:52:77:29:4a:75:aa:02:d8:af:53:24: c1 prime1: 00:ea:12:02:bb:5a:0f:5a:d8:a9:95:b2:ba:30:15: . . . [omitted for brevity] . . . 5b:ca:9c:7c:19:48:77:1e:5d prime2: 00:cd:82:da:84:71:1d:18:52:cb:c6:4d:74:14:be: . . . [omitted for brevity] . . . 5f:db:d5:5e:47:89:a7:ef:e3 exponent1: 32:37:62:f6:a6:bf:9c:91:d6:f0:12:c3:f7:04:e9: . . . [omitted for brevity] . . . 97:3e:33:31:89:66:64:d1 exponent2: 00:88:a2:e8:90:47:f8:75:34:8f:41:50:3b:ce:93: . . . [omitted for brevity] . . . ff:74:d4:be:f3:47:45:bd:cb coefficient: 4d:7c:09:4c:34:73:c4:26:f0:58:f5:e1:45:3c:af: . . . [omitted for brevity] . . . af:01:5f:af:ad:6a:09:bf Step 2: Sign the ELF File object By now you should have your private key, and obtained, by hook or crook, a cert (either from a CA or use one you created (a self-signed cert). The next step is to sign one or more objects with your private key and cert. Here's a simple example that creates an object file, signs, verifies, and lists the contents of the ELF signature. $ echo '#include <stdio.h>\nint main(){printf("Hello\\n");}'>hello.c $ make hello cc -o hello hello.c $ elfsign verify -v -c MYSELFSIGNED.pem -e hello elfsign: no signature found in hello. $ elfsign sign -F rsa_sha256 -v -k MYSELFSIGNED.key -c MYSELFSIGNED.pem -e hello elfsign: hello signed successfully. format: rsa_sha256. signer: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com. signed on: October 17, 2013 04:22:49 PM PDT. $ elfsign list -f format -e hello rsa_sha256 $ elfsign list -f signer -e hello O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com $ elfsign list -f time -e hello October 17, 2013 04:22:49 PM PDT $ elfsign verify -v -c MYSELFSIGNED.key -e hello elfsign: verification of hello failed. format: rsa_sha256. signer: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com. signed on: October 17, 2013 04:22:49 PM PDT. Signing using the pkcs11 keystore To sign the ELF file using a private key in the secure pkcs11 keystore, replace "-K MYSELFSIGNED.key" in the "elfsign sign" command line with "-T MYPRIVATEKEY", where MYPRIVATKEY is the pkcs11 token label. Step 3: Install the cert and test on another system Just signing the object isn't enough. You need to copy or install the cert and the signed ELF file(s) on another system to test that the signature is OK. Your public key cert should be installed in /etc/certs. Use elfsign verify to verify the signature. Elfsign verify checks each cert in /etc/certs until it finds one that matches the elfsign signature in the file. If one isn't found, the verification fails. Here's an example: $ su Password: # rm /etc/certs/MYSELFSIGNED.key # cp MYSELFSIGNED.pem /etc/certs # exit $ elfsign verify -v hello elfsign: verification of hello passed. format: rsa_sha256. signer: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com. signed on: October 17, 2013 04:24:20 PM PDT. After testing, package your cert along with your ELF object to allow elfsign verification after your cert and object are installed or copied. Under the Hood: elfsign verification Here's the steps taken to verify a ELF file signed with elfsign. The steps to sign the file are similar except the private key exponent is used instead of the public key exponent and the .SUNW_signature section is written to the ELF file instead of being read from the file. Generate a digest (SHA-256) of the ELF file sections. This digest uses all ELF sections loaded in memory, but excludes the ELF header, the .SUNW_signature section, and the symbol table Extract the RSA signature (RSA-2048) from the .SUNW_signature section Extract the RSA public key modulus and public key exponent (65537) from the public key cert Calculate the expected digest as follows:     signaturepublicKeyExponent % publicKeyModulus Strip the PKCS#1 padding (most significant bytes) from the above. The padding is 0x00, 0x01, 0xff, 0xff, . . ., 0xff, 0x00. If the actual digest == expected digest, the ELF file is verified (OK). Further Information elfsign(1), pktool(1), and openssl(1) man pages. "Signed Solaris 10 Binaries?" blog by Darren Moffat (2005) shows how to use elfsign. "Simple CLI based CA on Solaris" blog by Darren Moffat (2008) shows how to set up a simple CA for use with self-signed certificates. "How to Create a Certificate by Using the pktool gencert Command" System Administration Guide: Security Services (available at docs.oracle.com)

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  • Setting up a VPN connection to Amazon VPC - routing

    - by Keeno
    I am having some real issues setting up a VPN between out office and AWS VPC. The "tunnels" appear to be up, however I don't know if they are configured correctly. The device I am using is a Netgear VPN Firewall - FVS336GV2 If you see in the attached config downloaded from VPC (#3 Tunnel Interface Configuration), it gives me some "inside" addresses for the tunnel. When setting up the IPsec tunnels do I use the inside tunnel IP's (e.g. 169.254.254.2/30) or do I use my internal network subnet (10.1.1.0/24) I have tried both, when I tried the local network (10.1.1.x) the tracert stops at the router. When I tried with the "inside" ips, the tracert to the amazon VPC (10.0.0.x) goes out over the internet. this all leads me to the next question, for this router, how do I set up stage #4, the static next hop? What are these seemingly random "inside" addresses and where did amazon generate them from? 169.254.254.x seems odd? With a device like this, is the VPN behind the firewall? I have tweaked any IP addresses below so that they are not "real". I am fully aware, this is probably badly worded. Please if there is any further info/screenshots that will help, let me know. Amazon Web Services Virtual Private Cloud IPSec Tunnel #1 ================================================================================ #1: Internet Key Exchange Configuration Configure the IKE SA as follows - Authentication Method : Pre-Shared Key - Pre-Shared Key : --- - Authentication Algorithm : sha1 - Encryption Algorithm : aes-128-cbc - Lifetime : 28800 seconds - Phase 1 Negotiation Mode : main - Perfect Forward Secrecy : Diffie-Hellman Group 2 #2: IPSec Configuration Configure the IPSec SA as follows: - Protocol : esp - Authentication Algorithm : hmac-sha1-96 - Encryption Algorithm : aes-128-cbc - Lifetime : 3600 seconds - Mode : tunnel - Perfect Forward Secrecy : Diffie-Hellman Group 2 IPSec Dead Peer Detection (DPD) will be enabled on the AWS Endpoint. We recommend configuring DPD on your endpoint as follows: - DPD Interval : 10 - DPD Retries : 3 IPSec ESP (Encapsulating Security Payload) inserts additional headers to transmit packets. These headers require additional space, which reduces the amount of space available to transmit application data. To limit the impact of this behavior, we recommend the following configuration on your Customer Gateway: - TCP MSS Adjustment : 1387 bytes - Clear Don't Fragment Bit : enabled - Fragmentation : Before encryption #3: Tunnel Interface Configuration Your Customer Gateway must be configured with a tunnel interface that is associated with the IPSec tunnel. All traffic transmitted to the tunnel interface is encrypted and transmitted to the Virtual Private Gateway. The Customer Gateway and Virtual Private Gateway each have two addresses that relate to this IPSec tunnel. Each contains an outside address, upon which encrypted traffic is exchanged. Each also contain an inside address associated with the tunnel interface. The Customer Gateway outside IP address was provided when the Customer Gateway was created. Changing the IP address requires the creation of a new Customer Gateway. The Customer Gateway inside IP address should be configured on your tunnel interface. Outside IP Addresses: - Customer Gateway : 217.33.22.33 - Virtual Private Gateway : 87.222.33.42 Inside IP Addresses - Customer Gateway : 169.254.254.2/30 - Virtual Private Gateway : 169.254.254.1/30 Configure your tunnel to fragment at the optimal size: - Tunnel interface MTU : 1436 bytes #4: Static Routing Configuration: To route traffic between your internal network and your VPC, you will need a static route added to your router. Static Route Configuration Options: - Next hop : 169.254.254.1 You should add static routes towards your internal network on the VGW. The VGW will then send traffic towards your internal network over the tunnels. IPSec Tunnel #2 ================================================================================ #1: Internet Key Exchange Configuration Configure the IKE SA as follows - Authentication Method : Pre-Shared Key - Pre-Shared Key : --- - Authentication Algorithm : sha1 - Encryption Algorithm : aes-128-cbc - Lifetime : 28800 seconds - Phase 1 Negotiation Mode : main - Perfect Forward Secrecy : Diffie-Hellman Group 2 #2: IPSec Configuration Configure the IPSec SA as follows: - Protocol : esp - Authentication Algorithm : hmac-sha1-96 - Encryption Algorithm : aes-128-cbc - Lifetime : 3600 seconds - Mode : tunnel - Perfect Forward Secrecy : Diffie-Hellman Group 2 IPSec Dead Peer Detection (DPD) will be enabled on the AWS Endpoint. We recommend configuring DPD on your endpoint as follows: - DPD Interval : 10 - DPD Retries : 3 IPSec ESP (Encapsulating Security Payload) inserts additional headers to transmit packets. These headers require additional space, which reduces the amount of space available to transmit application data. To limit the impact of this behavior, we recommend the following configuration on your Customer Gateway: - TCP MSS Adjustment : 1387 bytes - Clear Don't Fragment Bit : enabled - Fragmentation : Before encryption #3: Tunnel Interface Configuration Outside IP Addresses: - Customer Gateway : 217.33.22.33 - Virtual Private Gateway : 87.222.33.46 Inside IP Addresses - Customer Gateway : 169.254.254.6/30 - Virtual Private Gateway : 169.254.254.5/30 Configure your tunnel to fragment at the optimal size: - Tunnel interface MTU : 1436 bytes #4: Static Routing Configuration: Static Route Configuration Options: - Next hop : 169.254.254.5 You should add static routes towards your internal network on the VGW. The VGW will then send traffic towards your internal network over the tunnels. EDIT #1 After writing this post, I continued to fiddle and something started to work, just not very reliably. The local IPs to use when setting up the tunnels where indeed my network subnets. Which further confuses me over what these "inside" IP addresses are for. The problem is, results are not consistent what so ever. I can "sometimes" ping, I can "sometimes" RDP using the VPN. Sometimes, Tunnel 1 or Tunnel 2 can be up or down. When I came back into work today, Tunnel 1 was down, so I deleted it and re-created it from scratch. Now I cant ping anything, but Amazon AND the router are telling me tunnel 1/2 are fine. I guess the router/vpn hardware I have just isnt up to the job..... EDIT #2 Now Tunnel 1 is up, Tunnel 2 is down (I didn't change any settings) and I can ping/rdp again. EDIT #3 Screenshot of route table that the router has built up. Current state (tunnel 1 still up and going string, 2 is still down and wont re-connect)

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  • Puppet's automatically generated certificates failing

    - by gparent
    I am running a default configuration of Puppet on Debian Squeeze 6.0.4. The server's FQDN is master.example.com. The client's FQDN is client.example.com. I am able to contact the puppet master and send a CSR. I sign it using puppetca -sa but the client will still not connect. Date of both machines is within 2 seconds of Tue Apr 3 20:59:00 UTC 2012 as I wrote this sentence. This is what appears in /var/log/syslog: Apr 3 17:03:52 localhost puppet-agent[18653]: Reopening log files Apr 3 17:03:52 localhost puppet-agent[18653]: Starting Puppet client version 2.6.2 Apr 3 17:03:53 localhost puppet-agent[18653]: Could not retrieve catalog from remote server: SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certificate verify failed Apr 3 17:03:53 localhost puppet-agent[18653]: Using cached catalog Apr 3 17:03:53 localhost puppet-agent[18653]: Could not retrieve catalog; skipping run Here is some interesting output: OpenSSL client test: client:~# openssl s_client -host master.example.com -port 8140 -cert /var/lib/puppet/ssl/certs/client.example.com.pem -key /var/lib/puppet/ssl/private_keys/client.example.com.pem -CAfile /var/lib/puppet/ssl/certs/ca.pem CONNECTED(00000003) depth=1 /CN=Puppet CA: master.example.com verify return:1 depth=0 /CN=master.example.com verify error:num=7:certificate signature failure verify return:1 depth=0 /CN=master.example.com verify return:1 18509:error:1409441B:SSL routines:SSL3_READ_BYTES:tlsv1 alert decrypt error:s3_pkt.c:1102:SSL alert number 51 18509:error:140790E5:SSL routines:SSL23_WRITE:ssl handshake failure:s23_lib.c:188: client:~# master's certificate: root@master:/etc/puppet# openssl x509 -text -noout -in /etc/puppet/ssl/certs/master.example.com.pem Certificate: Data: Version: 3 (0x2) Serial Number: 2 (0x2) Signature Algorithm: sha1WithRSAEncryption Issuer: CN=Puppet CA: master.example.com Validity Not Before: Apr 2 20:01:28 2012 GMT Not After : Apr 2 20:01:28 2017 GMT Subject: CN=master.example.com Subject Public Key Info: Public Key Algorithm: rsaEncryption RSA Public Key: (1024 bit) Modulus (1024 bit): 00:a9:c1:f9:4c:cd:0f:68:84:7b:f4:93:16:20:44: 7a:2b:05:8e:57:31:05:8e:9c:c8:08:68:73:71:39: c1:86:6a:59:93:6e:53:aa:43:11:83:5b:2d:8c:7d: 54:05:65:c1:e1:0e:94:4a:f0:86:58:c3:3d:4f:f3: 7d:bd:8e:29:58:a6:36:f4:3e:b2:61:ec:53:b5:38: 8e:84:ac:5f:a3:e3:8c:39:bd:cf:4f:3c:ff:a9:65: 09:66:3c:ba:10:14:69:d5:07:57:06:28:02:37:be: 03:82:fb:90:8b:7d:b3:a5:33:7b:9b:3a:42:51:12: b3:ac:dd:d5:58:69:a9:8a:ed Exponent: 65537 (0x10001) X509v3 extensions: X509v3 Basic Constraints: critical CA:FALSE Netscape Comment: Puppet Ruby/OpenSSL Internal Certificate X509v3 Key Usage: critical Digital Signature, Key Encipherment X509v3 Subject Key Identifier: 8C:2F:14:84:B6:A1:B5:0C:11:52:36:AB:E5:3F:F2:B9:B3:25:F3:1C X509v3 Extended Key Usage: critical TLS Web Server Authentication, TLS Web Client Authentication Signature Algorithm: sha1WithRSAEncryption 7b:2c:4f:c2:76:38:ab:03:7f:c6:54:d9:78:1d:ab:6c:45:ab: 47:02:c7:fd:45:4e:ab:b5:b6:d9:a7:df:44:72:55:0c:a5:d0: 86:58:14:ae:5f:6f:ea:87:4d:78:e4:39:4d:20:7e:3d:6d:e9: e2:5e:d7:c9:3c:27:43:a4:29:44:85:a1:63:df:2f:55:a9:6a: 72:46:d8:fb:c7:cc:ca:43:e7:e1:2c:fe:55:2a:0d:17:76:d4: e5:49:8b:85:9f:fa:0e:f6:cc:e8:28:3e:8b:47:b0:e1:02:f0: 3d:73:3e:99:65:3b:91:32:c5:ce:e4:86:21:b2:e0:b4:15:b5: 22:63 root@master:/etc/puppet# CA's certificate: root@master:/etc/puppet# openssl x509 -text -noout -in /etc/puppet/ssl/certs/ca.pem Certificate: Data: Version: 3 (0x2) Serial Number: 1 (0x1) Signature Algorithm: sha1WithRSAEncryption Issuer: CN=Puppet CA: master.example.com Validity Not Before: Apr 2 20:01:05 2012 GMT Not After : Apr 2 20:01:05 2017 GMT Subject: CN=Puppet CA: master.example.com Subject Public Key Info: Public Key Algorithm: rsaEncryption RSA Public Key: (1024 bit) Modulus (1024 bit): 00:b5:2c:3e:26:a3:ae:43:b8:ed:1e:ef:4d:a1:1e: 82:77:78:c2:98:3f:e2:e0:05:57:f0:8d:80:09:36: 62:be:6c:1a:21:43:59:1d:e9:b9:4d:e0:9c:fa:09: aa:12:a1:82:58:fc:47:31:ed:ad:ad:73:01:26:97: ef:d2:d6:41:6b:85:3b:af:70:00:b9:63:e9:1b:c3: ce:57:6d:95:0e:a6:d2:64:bd:1f:2c:1f:5c:26:8e: 02:fd:d3:28:9e:e9:8f:bc:46:bb:dd:25:db:39:57: 81:ed:e5:c8:1f:3d:ca:39:cf:e7:f3:63:75:f6:15: 1f:d4:71:56:ed:84:50:fb:5d Exponent: 65537 (0x10001) X509v3 extensions: X509v3 Basic Constraints: critical CA:TRUE Netscape Comment: Puppet Ruby/OpenSSL Internal Certificate X509v3 Key Usage: critical Certificate Sign, CRL Sign X509v3 Subject Key Identifier: 8C:2F:14:84:B6:A1:B5:0C:11:52:36:AB:E5:3F:F2:B9:B3:25:F3:1C Signature Algorithm: sha1WithRSAEncryption 1d:cd:c6:65:32:42:a5:01:62:46:87:10:da:74:7e:8b:c8:c9: 86:32:9e:c2:2e:c1:fd:00:79:f0:ef:d8:73:dd:7e:1b:1a:3f: cc:64:da:a3:38:ad:49:4e:c8:4d:e3:09:ba:bc:66:f2:6f:63: 9a:48:19:2d:27:5b:1d:2a:69:bf:4f:f4:e0:67:5e:66:84:30: e5:85:f4:49:6e:d0:92:ae:66:77:50:cf:45:c0:29:b2:64:87: 12:09:d3:10:4d:91:b6:f3:63:c4:26:b3:fa:94:2b:96:18:1f: 9b:a9:53:74:de:9c:73:a4:3a:8d:bf:fa:9c:c0:42:9d:78:49: 4d:70 root@master:/etc/puppet# Client's certificate: client:~# openssl x509 -text -noout -in /var/lib/puppet/ssl/certs/client.example.com.pem Certificate: Data: Version: 3 (0x2) Serial Number: 3 (0x3) Signature Algorithm: sha1WithRSAEncryption Issuer: CN=Puppet CA: master.example.com Validity Not Before: Apr 2 20:01:36 2012 GMT Not After : Apr 2 20:01:36 2017 GMT Subject: CN=client.example.com Subject Public Key Info: Public Key Algorithm: rsaEncryption RSA Public Key: (1024 bit) Modulus (1024 bit): 00:ae:88:6d:9b:e3:b1:fc:47:07:d6:bf:ea:53:d1: 14:14:9b:35:e6:70:43:e0:58:35:76:ac:c5:9d:86: 02:fd:77:28:fc:93:34:65:9d:dd:0b:ea:21:14:4d: 8a:95:2e:28:c9:a5:8d:a2:2c:0e:1c:a0:4c:fa:03: e5:aa:d3:97:98:05:59:3c:82:a9:7c:0e:e9:df:fd: 48:81:dc:33:dc:88:e9:09:e4:19:d6:e4:7b:92:33: 31:73:e4:f2:9c:42:75:b2:e1:9f:d9:49:8c:a7:eb: fa:7d:cb:62:22:90:1c:37:3a:40:95:a7:a0:3b:ad: 8e:12:7c:6e:ad:04:94:ed:47 Exponent: 65537 (0x10001) X509v3 extensions: X509v3 Basic Constraints: critical CA:FALSE Netscape Comment: Puppet Ruby/OpenSSL Internal Certificate X509v3 Key Usage: critical Digital Signature, Key Encipherment X509v3 Subject Key Identifier: 8C:2F:14:84:B6:A1:B5:0C:11:52:36:AB:E5:3F:F2:B9:B3:25:F3:1C X509v3 Extended Key Usage: critical TLS Web Server Authentication, TLS Web Client Authentication Signature Algorithm: sha1WithRSAEncryption 33:1f:ec:3c:91:5a:eb:c6:03:5f:a1:58:60:c3:41:ed:1f:fe: cb:b2:40:11:63:4d:ba:18:8a:8b:62:ba:ab:61:f5:a0:6c:0e: 8a:20:56:7b:10:a1:f9:1d:51:49:af:70:3a:05:f9:27:4a:25: d4:e6:88:26:f7:26:e0:20:30:2a:20:1d:c4:d3:26:f1:99:cf: 47:2e:73:90:bd:9c:88:bf:67:9e:dd:7c:0e:3a:86:6b:0b:8d: 39:0f:db:66:c0:b6:20:c3:34:84:0e:d8:3b:fc:1c:a8:6c:6c: b1:19:76:65:e6:22:3c:bf:ff:1c:74:bb:62:a0:46:02:95:fa: 83:41 client:~#

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  • Depth interpolation for z-buffer, with scanline

    - by Twodordan
    I have to write my own software 3d rasterizer, and so far I am able to project my 3d model made of triangles into 2d space: I rotate, translate and project my points to get a 2d space representation of each triangle. Then, I take the 3 triangle points and I implement the scanline algorithm (using linear interpolation) to find all points[x][y] along the edges(left and right) of the triangles, so that I can scan the triangle horizontally, row by row, and fill it with pixels. This works. Except I have to also implement z-buffering. This means that knowing the rotated&translated z coordinates of the 3 vertices of the triangle, I must interpolate the z coordinate for all other points I find with my scanline algorithm. The concept seems clear enough, I first find Za and Zb with these calculations: var Z_Slope = (bottom_point_z - top_point_z) / (bottom_point_y - top_point_y); var Za = top_point_z + ((current_point_y - top_point_y) * Z_Slope); Then for each Zp I do the same interpolation horizontally: var Z_Slope = (right_z - left_z) / (right_x - left_x); var Zp = left_z + ((current_point_x - left_x) * Z_Slope); And of course I add to the zBuffer, if current z is closer to the viewer than the previous value at that index. (my coordinate system is x: left - right; y: top - bottom; z: your face - computer screen;) The problem is, it goes haywire. The project is here and if you select the "Z-Buffered" radio button, you'll see the results... (note that the rest of the options before "Z-Buffered" use the Painter's algorithm to correctly order the triangles. I also use the painter's algorithm -only- to draw the wireframe in "Z-Buffered" mode for debugging purposes) PS: I've read here that you must turn the z's into their reciprocals (meaning z = 1/z) before you interpolate. I tried that, and it appears that there's no change. What am I missing? (could anyone clarify, precisely where you must turn z into 1/z and where to turn it back?)

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  • Do I need path finding to make AI avoid obstacles?

    - by yannicuLar
    How do you know when a path-finding algorithm is really needed? There are contexts, where you just want to improve AI navigation to avoid an object, like a space -ship that won't crash on a planet or a car that already knows where to steer, but needs small corrections to avoid a road bump. As I've seen on similar posts, the obvious solution is to implement some path-finding algorithm, most likely like A*, and let your AI-controlled object to navigate through the path. Now, I have the necessary skills to implement a path-finding algorithm, and I'm not being lazy here, but I'm still a bit skeptical on if this is really needed. I have the impression that path-finding is appropriate to navigate through a maze, or picking a path when there are many alternatives. But in obstacle avoidance, when you do know the path, but need to make slight corrections, is path finding really necessary? Even when the obstacles are too sparse or small ? I mean, in real life, when you're driving and notice a bump on the road, you will just have to pick between steering a bit on the left (and have the bump on your right side) or the other way around. You will not consider stopping, or going backwards. A path finding would be appropriate when you need to pick a route through the city, right ? So, are there any other methods to help AI navigation, except path-finding? And if there are, how do you know when path-fining is the appropriate algorithm ? Thanks for any thoughts

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  • A Cautionary Tale About Multi-Source JNDI Configuration

    - by scott.s.nelson(at)oracle.com
    Here's a bit of fun with WebLogic JDBC configurations.  I ran into this issue after reading that p13nDataSource and cgDataSource-NonXA should not be configured as multi-source. There were some issues changing them to use the basic JDBC connection string and when rolling back to the bad configuration the server went "Boom".  Since one purpose behind this blog is to share lessons learned, I just had to post this. If you write your descriptors manually (as opposed to generating them using the WLS console) and put a comma-separated list of JNDI addresses like this: <jdbc-data-source-params> <jndi-name>weblogic.jdbc.jts.commercePool,contentDataSource, contentVersioningDataSource,portalFrameworkPool</jndi-name> <algorithm-type>Load-Balancing</algorithm-type> <data-source-list>portalDataSource-rac0,portalDataSource-rac1</data-source-list> <failover-request-if-busy>false</failover-request-if-busy> </jdbc-data-source-params> so long as the first address resolves, it will still work. Sort of.  If you call this connection to do an update, only one node of the RAC instance is updated. Other wonderful side-effects include the server refusing to start sometimes. The proper way to list the JNDI sources is one per node, like this: <jdbc-data-source-params> <jndi-name>weblogic.jdbc.jts.commercePool</jndi-name> <jndi-name>contentDataSource</jndi-name> <jndi-name>contentVersioningDataSource</jndi-name> <jndi-name>portalFrameworkPool</jndi-name> <algorithm-type>Load-Balancing</algorithm-type> <data-source-list>portalDataSource-rac0, portalDataSource-rac1, portalDataSource-rac2 </data-source-list> <failover-request-if-busy>false</failover-request-if-busy> </jdbc-data-source-params>(Props to Sandeep Seshan for locating the root cause)

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  • A new mission statement for my school's algorithms class

    - by Eric Fode
    The teacher at Eastern Washington University that is now teaching the algorithms course is new to eastern and as a result the course has changed drastically mostly in the right direction. That being said I feel that the class could use a more specific, and industry oriented (since that is where most students will go, though suggestions for an academia oriented class are also welcome) direction, having only worked in industry for 2 years I would like the community's (a wider and much more collectively experienced and in the end plausibly more credible) opinion on the quality of this as a statement for the purpose an algorithms class, and if I am completely off target your suggestion for the purpose of a required Jr. level Algorithms class that is standalone (so no other classes focusing specifically on algorithms are required). The statement is as follows: The purpose of the algorithms class is to do three things: Primarily, to teach how to learn, do basic analysis, and implement a given algorithm found outside of the class. Secondly, to teach the student how to model a problem in their mind so that they can find a an existing algorithm or have a direction to start the development of a new algorithm. Third, to overview a variety of algorithms that exist and to deeply understand and analyze one algorithm in each of the basic algorithmic design strategies: Divide and Conquer, Reduce and Conquer, Transform and Conquer, Greedy, Brute Force, Iterative Improvement and Dynamic Programming. The Question in short is: do you agree with this statement of the purpose of an algorithms course, so that it would be useful in the real world, if not what would you suggest?

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  • Find points whose pairwise distances approximate a given distance matrix

    - by Stephan Kolassa
    Problem. I have a symmetric distance matrix with entries between zero and one, like this one: D = ( 0.0 0.4 0.0 0.5 ) ( 0.4 0.0 0.2 1.0 ) ( 0.0 0.2 0.0 0.7 ) ( 0.5 1.0 0.7 0.0 ) I would like to find points in the plane that have (approximately) the pairwise distances given in D. I understand that this will usually not be possible with strictly correct distances, so I would be happy with a "good" approximation. My matrices are smallish, no more than 10x10, so performance is not an issue. Question. Does anyone know of an algorithm to do this? Background. I have sets of probability densities between which I calculate Hellinger distances, which I would like to visualize as above. Each set contains no more than 10 densities (see above), but I have a couple of hundred sets. What I did so far. I did consider posting at math.SE, but looking at what gets tagged as "geometry" there, it seems like this kind of computational geometry question would be more on-topic here. If the community thinks this should be migrated, please go ahead. This looks like a straightforward problem in computational geometry, and I would assume that anyone involved in clustering might be interested in such a visualization, but I haven't been able to google anything. One simple approach would be to randomly plonk down points and perturb them until the distance matrix is close to D, e.g., using Simulated Annealing, or run a Genetic Algorithm. I have to admit that I haven't tried that yet, hoping for a smarter way. One specific operationalization of a "good" approximation in the sense above is Problem 4 in the Open Problems section here, with k=2. Now, while finding an algorithm that is guaranteed to find the minimum l1-distance between D and the resulting distance matrix may be an open question, it still seems possible that there at least is some approximation to this optimal solution. If I don't get an answer here, I'll mail the gentleman who posed that problem and ask whether he knows of any approximation algorithm (and post any answer I get to that here).

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  • creating objects from trivial graph format text file. java. dijkstra algorithm.

    - by user560084
    i want to create objects, vertex and edge, from trivial graph format txt file. one of programmers here suggested that i use trivial graph format to store data for dijkstra algorithm. the problem is that at the moment all the information, e.g., weight, links, is in the sourcecode. i want to have a separate text file for that and read it into the program. i thought about using a code for scanning through the text file by using scanner. but i am not quite sure how to create different objects from the same file. could i have some help please? the file is v0 Harrisburg v1 Baltimore v2 Washington v3 Philadelphia v4 Binghamton v5 Allentown v6 New York # v0 v1 79.83 v0 v5 81.15 v1 v0 79.75 v1 v2 39.42 v1 v3 103.00 v2 v1 38.65 v3 v1 102.53 v3 v5 61.44 v3 v6 96.79 v4 v5 133.04 v5 v0 81.77 v5 v3 62.05 v5 v4 134.47 v5 v6 91.63 v6 v3 97.24 v6 v5 87.94 and the dijkstra algorithm code is Downloaded from: http://en.literateprograms.org/Special:Downloadcode/Dijkstra%27s_algorithm_%28Java%29 */ import java.util.PriorityQueue; import java.util.List; import java.util.ArrayList; import java.util.Collections; class Vertex implements Comparable<Vertex> { public final String name; public Edge[] adjacencies; public double minDistance = Double.POSITIVE_INFINITY; public Vertex previous; public Vertex(String argName) { name = argName; } public String toString() { return name; } public int compareTo(Vertex other) { return Double.compare(minDistance, other.minDistance); } } class Edge { public final Vertex target; public final double weight; public Edge(Vertex argTarget, double argWeight) { target = argTarget; weight = argWeight; } } public class Dijkstra { public static void computePaths(Vertex source) { source.minDistance = 0.; PriorityQueue<Vertex> vertexQueue = new PriorityQueue<Vertex>(); vertexQueue.add(source); while (!vertexQueue.isEmpty()) { Vertex u = vertexQueue.poll(); // Visit each edge exiting u for (Edge e : u.adjacencies) { Vertex v = e.target; double weight = e.weight; double distanceThroughU = u.minDistance + weight; if (distanceThroughU < v.minDistance) { vertexQueue.remove(v); v.minDistance = distanceThroughU ; v.previous = u; vertexQueue.add(v); } } } } public static List<Vertex> getShortestPathTo(Vertex target) { List<Vertex> path = new ArrayList<Vertex>(); for (Vertex vertex = target; vertex != null; vertex = vertex.previous) path.add(vertex); Collections.reverse(path); return path; } public static void main(String[] args) { Vertex v0 = new Vertex("Nottinghill_Gate"); Vertex v1 = new Vertex("High_Street_kensignton"); Vertex v2 = new Vertex("Glouchester_Road"); Vertex v3 = new Vertex("South_Kensignton"); Vertex v4 = new Vertex("Sloane_Square"); Vertex v5 = new Vertex("Victoria"); Vertex v6 = new Vertex("Westminster"); v0.adjacencies = new Edge[]{new Edge(v1, 79.83), new Edge(v6, 97.24)}; v1.adjacencies = new Edge[]{new Edge(v2, 39.42), new Edge(v0, 79.83)}; v2.adjacencies = new Edge[]{new Edge(v3, 38.65), new Edge(v1, 39.42)}; v3.adjacencies = new Edge[]{new Edge(v4, 102.53), new Edge(v2, 38.65)}; v4.adjacencies = new Edge[]{new Edge(v5, 133.04), new Edge(v3, 102.53)}; v5.adjacencies = new Edge[]{new Edge(v6, 81.77), new Edge(v4, 133.04)}; v6.adjacencies = new Edge[]{new Edge(v0, 97.24), new Edge(v5, 81.77)}; Vertex[] vertices = { v0, v1, v2, v3, v4, v5, v6 }; computePaths(v0); for (Vertex v : vertices) { System.out.println("Distance to " + v + ": " + v.minDistance); List<Vertex> path = getShortestPathTo(v); System.out.println("Path: " + path); } } } and the code for scanning file is import java.util.Scanner; import java.io.File; import java.io.FileNotFoundException; public class DataScanner1 { //private int total = 0; //private int distance = 0; private String vector; private String stations; private double [] Edge = new double []; /*public int getTotal(){ return total; } */ /* public void getMenuInput(){ KeyboardInput in = new KeyboardInput; System.out.println("Enter the destination? "); String val = in.readString(); return val; } */ public void readFile(String fileName) { try { Scanner scanner = new Scanner(new File(fileName)); scanner.useDelimiter (System.getProperty("line.separator")); while (scanner.hasNext()) { parseLine(scanner.next()); } scanner.close(); } catch (FileNotFoundException e) { e.printStackTrace(); } } public void parseLine(String line) { Scanner lineScanner = new Scanner(line); lineScanner.useDelimiter("\\s*,\\s*"); vector = lineScanner.next(); stations = lineScanner.next(); System.out.println("The current station is " + vector + " and the destination to the next station is " + stations + "."); //total += distance; //System.out.println("The total distance is " + total); } public static void main(String[] args) { /* if (args.length != 1) { System.err.println("usage: java TextScanner2" + "file location"); System.exit(0); } */ DataScanner1 scanner = new DataScanner1(); scanner.readFile(args[0]); //int total =+ distance; //System.out.println(""); //System.out.println("The total distance is " + scanner.getTotal()); } }

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  • Diagonal line of sight with two corners

    - by Ash Blue
    Right now I'm using Bresenham's line algorithm for line of sight. The problem is I've found an edge case where players can look through walls. Occurs when the player looks between two corners of a wall with a gap on the other side at specific angles. The result I want is for the tile between two walls to be marked invalid as so. What is the fastest way to modify Bresenham's line algorithm to solve this? If there isn't a good solution, is there a better suited algorithm? Any ideas are welcome. Please note the solution should also be capable of supporting 3d. Edit: For the working source code and an interactive demo of the completed product please see http://ashblue.github.io/javascript-pathfinding/

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