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• Encoding / Error Correction Challenge

  - by emi1faber

  Is it mathematically feasible to encode and initial 4 byte message into 8 bytes and if one of the 8 bytes is completely dropped and another is wrong to reconstruct the initial 4 byte message? There would be no way to retransmit nor would the location of the dropped byte be known. If one uses Reed Solomon error correction with 4 "parity" bytes tacked on to the end of the 4 "data" bytes, such as DDDDPPPP, and you end up with DDDEPPP (where E is an error) and a parity byte has been dropped, I don't believe there's a way to reconstruct the initial message (although correct me if I am wrong)... What about multiplying (or performing another mathematical operation) the initial 4 byte message by a constant, then utilizing properties of an inverse mathematical operation to determine what byte was dropped. Or, impose some constraints on the structure of the message so every other byte needs to be odd and the others need to be even. Alternatively, instead of bytes, it could also be 4 decimal digits encoded in some fashion into 8 decimal digits where errors could be detected & corrected under the same circumstances mentioned above - no retransmission and the location of the dropped byte is not known. I'm looking for any crazy ideas anyone might have... Any ideas out there?

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• Why this base64 function stop working when increasing max length?

  - by flyout

  I am using this class to encode/decode text to base64. It works fine with MAX_LEN up to 512 but if I increase it to 1024 the decode function returns and empty var. This is the function: char* Base64::encode(char *src) { char* ptr = dst+0; unsigned triad; unsigned int d_len = MAX_LEN; memset(dst,'\0', MAX_LEN); unsigned s_len = strlen(src); for (triad = 0; triad < s_len; triad += 3) { unsigned long int sr = 0; unsigned byte; for (byte = 0; (byte<3)&&(triad+byte<s_len); ++byte) { sr <<= 8; sr |= (*(src+triad+byte) & 0xff); } sr <<= (6-((8*byte)%6))%6; // shift left to next 6bit alignment if (d_len < 4) return NULL; // error - dest too short *(ptr+0) = *(ptr+1) = *(ptr+2) = *(ptr+3) = '='; switch(byte) { case 3: *(ptr+3) = base64[sr&0x3f]; sr >>= 6; case 2: *(ptr+2) = base64[sr&0x3f]; sr >>= 6; case 1: *(ptr+1) = base64[sr&0x3f]; sr >>= 6; *(ptr+0) = base64[sr&0x3f]; } ptr += 4; d_len -= 4; } return dst; } Why could be causing this?

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• Android AES and init vector

  - by Donald_W

  I have an issue with AES encryptio and decryption: I can change my IV entirely and still I'm able to decode my data. public static final byte[] IV = { 65, 1, 2, 23, 4, 5, 6, 7, 32, 21, 10, 11, 12, 13, 84, 45 }; public static final byte[] IV2 = { 65, 1, 2, 23, 45, 54, 61, 81, 32, 21, 10, 121, 12, 13, 84, 45 }; public static final byte[] KEY = { 0, 42, 2, 54, 4, 45, 6, 7, 65, 9, 54, 11, 12, 13, 60, 15 }; public static final byte[] KEY2 = { 0, 42, 2, 54, 43, 45, 16, 17, 65, 9, 54, 11, 12, 13, 60, 15 }; //public static final int BITS = 256; public static void test() { try { // encryption Cipher c = Cipher.getInstance("AES"); SecretKeySpec keySpec = new SecretKeySpec(KEY, "AES"); c.init(Cipher.ENCRYPT_MODE, keySpec, new IvParameterSpec(IV)); String s = "Secret message"; byte[] data = s.getBytes(); byte[] encrypted = c.doFinal(data); String encryptedStr = ""; for (int i = 0; i < encrypted.length; i++) encryptedStr += (char) encrypted[i]; //decryoption Cipher d_c = Cipher.getInstance("AES"); SecretKeySpec d_keySpec = new SecretKeySpec(KEY, "AES"); d_c.init(Cipher.DECRYPT_MODE, d_keySpec, new IvParameterSpec(IV2)); byte[] decrypted = d_c.doFinal(encrypted); String decryptedStr = ""; for (int i = 0; i < decrypted.length; i++) decryptedStr += (char) decrypted[i]; Log.d("", decryptedStr); } catch (Exception ex) { Log.d("", ex.getMessage()); } } Any ideas what I'm doing wrong? How can I get 256 bit AES encryption (only change key to 32-byte long array?) Encryption is a new topic for me so please for newbie friendly answers.

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• Reverse reading WORD from a binary file?

  - by Angel

  Hi, I have a structure: struct JFIF_HEADER { WORD marker[2]; // = 0xFFD8FFE0 WORD length; // = 0x0010 BYTE signature[5]; // = "JFIF\0" BYTE versionhi; // = 1 BYTE versionlo; // = 1 BYTE xyunits; // = 0 WORD xdensity; // = 1 WORD ydensity; // = 1 BYTE thumbnwidth; // = 0 BYTE thumbnheight; // = 0 }; This is how I read it from the file: HANDLE file = CreateFile(filename, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0); DWORD tmp = 0; DWORD size = GetFileSize(file, &tmp); BYTE *DATA = new BYTE[size]; ReadFile(file, DATA, size, &tmp, 0); JFIF_HEADER header; memcpy(&header, DATA, sizeof(JFIF_HEADER)); This is how the beginning of my file looks in hex editor: 0xFF 0xD8 0xFF 0xE0 0x00 0x10 0x4A 0x46 0x49 0x46 0x00 0x01 0x01 0x00 0x00 0x01 When I print header.marker, it shows exactly what it should (0xFFD8FFE0). But when I print header.length, it shows 0x1000 instead of 0x0010. The same thing is with xdensity and ydensity. Why do I get wrong data when reading a WORD? Thank you.

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• How to set buffer size in client-server app using sockets?

  - by nelly

  First of all i am new to networking so i may say dumb thing in here. Considering a client-server application using sockets(.net with c# if that matters). The client sends some data, the server process it and sends back a string. The client sends some other data, the serve process it, queries the db and sends back several hundreds of items from the database The client sends some other type of data and the server notifies some other clients . My question is how to set the buffer size correctly for reading/writing operation. Should i do something like this: byte[] buff = new byte[client.ReceiveBufferSize] ? I am thinking of something like this: Client sends data to the server(and the server will follow the same pattern) byte[] bytesToSend=new byte[2048] //2048 to be standard for any command send by the client bytes 0..1 ->command type bytes 1..2047 ->command parameters byte[] bytesToReceive=new byte[8]/byte[64]/byte[8192] //switch(command type) But..what is happening when a client is notified by the server without sending data? What is the correct way to accomplish what i am trying to do? Thanks for reading.

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• LINQ and ordering of the result set

  - by vik20000in

  After filtering and retrieving the records most of the time (if not always) we have to sort the record in certain order. The sort order is very important for displaying records or major calculations. In LINQ for sorting data the order keyword is used. With the help of the order keyword we can decide on the ordering of the result set that is retrieved after the query.  Below is an simple example of the order keyword in LINQ.     string[] words = { "cherry", "apple", "blueberry" };     var sortedWords =         from word in words         orderby word         select word; Here we are ordering the data retrieved based on the string ordering. If required the order can also be made on any of the property of the individual like the length of the string.     var sortedWords =         from word in words         orderby word.Length         select word; You can also make the order descending or ascending by adding the keyword after the parameter.     var sortedWords =         from word in words         orderby word descending         select word; But the best part of the order clause is that instead of just passing a field you can also pass the order clause an instance of any class that implements IComparer interface. The IComparer interface holds a method Compare that Has to be implemented. In that method we can write any logic whatsoever for the comparision. In the below example we are making a string comparison by ignoring the case. string[] words = { "aPPLE", "AbAcUs", "bRaNcH", "BlUeBeRrY", "cHeRry"}; var sortedWords = words.OrderBy(a => a, new CaseInsensitiveComparer());  public class CaseInsensitiveComparer : IComparer<string> {     public int Compare(string x, string y)     {         return string.Compare(x, y, StringComparison.OrdinalIgnoreCase);     } }  But while sorting the data many a times we want to provide more than one sort so that data is sorted based on more than one condition. This can be achieved by proving the next order followed by a comma.     var sortedWords =         from word in words         orderby word , word.length         select word; We can also use the reverse() method to reverse the full order of the result set.     var sortedWords =         from word in words         select word.Reverse();                                 Vikram

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• How do you get Matlab to write the BOM (byte order markers) for UTF-16 text files?

  - by Richard Povinelli

  I am creating UTF16 text files with Matlab, which I am later reading in using Java. In Matlab, I open a file called fileName and write to it as follows: fid = fopen(fileName, 'w','n','UTF16-LE'); fprintf(fid,"Some stuff."); In Java, I can read the text file using the following code: FileInputStream fileInputStream = new FileInputStream(fileName); Scanner scanner = new Scanner(fileInputStream, "UTF-16LE"); String s = scanner.nextLine(); Here is the hex output: Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 00000000 73 00 6F 00 6D 00 65 00 20 00 73 00 74 00 75 00 66 00 66 00 s.o.m.e. .s.t.u.f.f. The above approach works fine. But, I want to be able to write out the file using UTF16 with a BOM to give me more flexibility so that I don't have to worry about big or little endian. In Matlab, I've coded: fid = fopen(fileName, 'w','n','UTF16'); fprintf(fid,"Some stuff."); In Java, I change the code to: FileInputStream fileInputStream = new FileInputStream(fileName); Scanner scanner = new Scanner(fileInputStream, "UTF-16"); String s = scanner.nextLine(); In this case, the string s is garbled, because Matlab is not writing the BOM. I can get the Java code to work just fine if I add the BOM manually. With the added BOM, the following file works fine. Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 00000000 FF FE 73 00 6F 00 6D 00 65 00 20 00 73 00 74 00 75 00 66 00 66 00 ÿþs.o.m.e. .s.t.u.f.f. How can I get Matlab to write out the BOM? I know I could write the BOM out separately, but I'd rather have Matlab do it automatically. Addendum I selected the answer below from Amro because it exactly solves the question I posed. One key discovery for me was the difference between the Unicode Standard and a UTF (Unicode transformation format) (see http://unicode.org/faq/utf_bom.html). The Unicode Standard provides unique identifiers (code points) for characters. UTFs provide mappings of every code point "to a unique byte sequence." Since all but a handful of the characters I am using are in the first 128 code points, I'm going to switch to using UTF-8 as Romeo suggests. UTF-8 is supported by Matlab (The warning shown below won't need to be suppressed.) and Java, and for my application will generate smaller text files. I suppress the Matlab warning Warning: The encoding 'UTF-16LE' is not supported. with warning off MATLAB:iofun:UnsupportedEncoding;

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• Possible SWITCH Optimization in DAX – #powerpivot #dax #tabular

  - by Marco Russo (SQLBI)

  In one of the Advanced DAX Workshop I taught this year, I had an interesting discussion about how to optimize a SWITCH statement (which could be frequently used checking a slicer, like in the Parameter Table pattern). Let’s start with the problem. What happen when you have such a statement? Sales :=     SWITCH (         VALUES ( Period[Period] ),         "Current", [Internet Total Sales],         "MTD", [MTD Sales],         "QTD", [QTD Sales],         "YTD", [YTD Sales],          BLANK ()     ) The SWITCH statement is in reality just syntax sugar for a nested IF statement. When you place such a measure in a pivot table, for every cell of the pivot table the IF options are evaluated. In order to optimize performance, the DAX engine usually does not compute cell-by-cell, but tries to compute the values in bulk-mode. However, if a measure contains an IF statement, every cell might have a different execution path, so the current implementation might evaluate all the possible IF branches in bulk-mode, so that for every cell the result from one of the branches will be already available in a pre-calculated dataset. The price for that could be high. If you consider the previous Sales measure, the YTD Sales measure could be evaluated for all the cells where it’s not required, and also when YTD is not selected at all in a Pivot Table. The actual optimization made by the DAX engine could be different in every build, and I expect newer builds of Tabular and Power Pivot to be better than older ones. However, we still don’t live in an ideal world, so it could be better trying to help the engine finding a better execution plan. One student (Niek de Wit) proposed this approach: Selection := IF (     HASONEVALUE ( Period[Period] ),     VALUES ( Period[Period] ) ) Sales := CALCULATE (     [Internet Total Sales],     FILTER (         VALUES ( 'Internet Sales'[Order Quantity] ),         'Internet Sales'[Order Quantity]             = IF (                 [Selection] = "Current",                 'Internet Sales'[Order Quantity],                 -1             )     ) )     + CALCULATE (         [MTD Sales],         FILTER (             VALUES ( 'Internet Sales'[Order Quantity] ),             'Internet Sales'[Order Quantity]                 = IF (                     [Selection] = "MTD",                     'Internet Sales'[Order Quantity],                     -1                 )         )     )     + CALCULATE (         [QTD Sales],         FILTER (             VALUES ( 'Internet Sales'[Order Quantity] ),             'Internet Sales'[Order Quantity]                 = IF (                     [Selection] = "QTD",                     'Internet Sales'[Order Quantity],                     -1                 )         )     )     + CALCULATE (         [YTD Sales],         FILTER (             VALUES ( 'Internet Sales'[Order Quantity] ),             'Internet Sales'[Order Quantity]                 = IF (                     [Selection] = "YTD",                     'Internet Sales'[Order Quantity],                     -1                 )         )     ) At first sight, you might think it’s impossible that this approach could be faster. However, if you examine with the profiler what happens, there is a different story. Every original IF’s execution branch is now a separate CALCULATE statement, which applies a filter that does not execute the required measure calculation if the result of the FILTER is empty. I used the ‘Internet Sales’[Order Quantity] column in this example just because in Adventure Works it has only one value (every row has 1): in the real world, you should use a column that has a very low number of distinct values, or use a column that has always the same value for every row (so it will be compressed very well!). Because the value –1 is never used in this column, the IF comparison in the filter discharge all the values iterated in the filter if the selection does not match with the desired value. I hope to have time in the future to write a longer article about this optimization technique, but in the meantime I’ve seen this optimization has been useful in many other implementations. Please write your feedback if you find scenarios (in both Power Pivot and Tabular) where you obtain performance improvements using this technique!

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• Send large JSON data to WCF Rest Service

  - by Christo Fur

  Hi I have a client web page that is sending a large json object to a proxy service on the same domain as the web page. The proxy (an ashx handler) then forwards the request to a WCF Rest Service. Using a WebClient object (standard .net object for making a http request) The JSON successfully arrives at the proxy via a jQuery POST on the client webpage. However, when the proxy forwards this to the WCF service I get a Bad Request - Error 400 This doesn't happen when the size of the json data is small The WCF service contract looks like this [WebInvoke(Method = "POST", BodyStyle = WebMessageBodyStyle.Wrapped, RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json)] [OperationContract] CarConfiguration CreateConfiguration(CarConfiguration configuration); And the DataContract like this [DataContract(Namespace = "")] public class CarConfiguration { [DataMember(Order = 1)] public int CarConfigurationId { get; set; } [DataMember(Order = 2)] public int UserId { get; set; } [DataMember(Order = 3)] public string Model { get; set; } [DataMember(Order = 4)] public string Colour { get; set; } [DataMember(Order = 5)] public string Trim { get; set; } [DataMember(Order = 6)] public string ThumbnailByteData { get; set; } [DataMember(Order = 6)] public string Wheel { get; set; } [DataMember(Order = 7)] public DateTime Date { get; set; } [DataMember(Order = 8)] public List<string> Accessories { get; set; } [DataMember(Order = 9)] public string Vehicle { get; set; } [DataMember(Order = 10)] public Decimal Price { get; set; } } When the ThumbnailByteData field is small, all is OK. When it is large I get the 400 error What are my options here? I've tried increasing the MaxBytesRecived config setting but that is not enough Any ideas?

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• Save blob to DB using hibernate

  - by Link123

  Hey! I tried save file to MySQL using blob with hibernate3. But I always have java.lang.UnsupportedOperationException: Blob may not be manipulated from creating session org.hibernate.lob.BlobImpl.excep(BlobImpl.java:127) Here some code. package com.uni.domain; public class File extends Identifier { private byte[] data; private String contentType; public byte[] getData() { return data; } public File() {} public void setData(byte[] photo) { this.data = photo; } public boolean isNew() { return true; } public String getContentType() { return contentType; } public void setContentType(String contentType) { this.contentType = contentType; } } package com.uni.domain; import org.hibernate.Hibernate; import org.hibernate.HibernateException; import org.hibernate.usertype.UserType; import java.io.InputStream; import java.io.OutputStream; import java.io.Serializable; import java.sql.*; import java.util.Arrays; public class PhotoType implements UserType { public int[] sqlTypes() { return new int[]{Types.BLOB}; } public Class returnedClass() { return byte[].class; } public boolean equals(Object o, Object o1) throws HibernateException { return Arrays.equals((byte[]) o, (byte[]) o1); } public int hashCode(Object o) throws HibernateException { return o.hashCode(); } public Object nullSafeGet(ResultSet resultSet, String[] strings, Object o) throws HibernateException, SQLException { Blob blob = resultSet.getBlob(strings[0]); return blob.getBytes(1, (int) blob.length()); } public void nullSafeSet(PreparedStatement st, Object value, int index) throws HibernateException, SQLException { st.setBlob(index, Hibernate.createBlob((byte[]) value)); } public Object deepCopy(Object value) { if (value == null) return null; byte[] bytes = (byte[]) value; byte[] result = new byte[bytes.length]; System.arraycopy(bytes, 0, result, 0, bytes.length); return result; } public boolean isMutable() { return true; } public Serializable disassemble(Object o) throws HibernateException { return null; . } public Object assemble(Serializable serializable, Object o) throws HibernateException { return null; . } public Object replace(Object o, Object o1, Object o2) throws HibernateException { return null; . } <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.uni.domain"> <class name="com.uni.domain.File"> <id name="id"> <generator class="native"/> </id> <property name="data" type="com.uni.domain.FleType"/> <property name="contentType"/> </class> </hibernate-mapping> Help me please. Where I’m wrong?

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• Flex: Double click event propagation on datagrid dependent on component order?

  - by MyMacAndMe

  I'd like to have a double click event on a datagrid in Flex3. The following example only works if the Accordion (id = "mustBeSecond") container comes after the DataGrid. Why is the order of the components important and what can I do to prevent this behavior? (The example does not work. If you change the order of "mustBeSecond" and "gridReportConversions" the example works fine) <mx:Script> <![CDATA[ import mx.controls.Alert; import mx.collections.ArrayCollection; [Bindable] private var dp:ArrayCollection = new ArrayCollection([ {qty:1,referer:'http://google.com'}, {qty:25,referer:'http://cnn.com'}, {qty:4,referer:'http:stackoverflow.com'}]); private function refererRowDoubleClicked(e:Event):void { Alert.show("double click"); } ]]> </mx:Script> <mx:HBox width="100%" height="100%"> <mx:Accordion width="200" height="200" id="mustBeSecond"> <mx:Canvas label="Navigation Box" width="100%" height="100%"> <mx:VBox> <mx:LinkButton label="First Link" /> <mx:LinkButton label="Second Link" /> </mx:VBox> </mx:Canvas> </mx:Accordion> <mx:DataGrid id="gridReportConversions" height="100%" width="100%" dataProvider="{this.dp}" mouseEnabled="true" doubleClickEnabled="true" itemDoubleClick="refererRowDoubleClicked(event)"> <mx:columns> <mx:DataGridColumn width="75" dataField="qty" headerText="Qty" /> <mx:DataGridColumn dataField="referer" headerText="URL" /> </mx:columns> </mx:DataGrid> </mx:HBox>

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• how to display the decrypted and splited Strings in order?

  - by sebby_zml

  Hi everyone, i need some help and guidance in displaying the splitted Strings in order. let say, i have username, password, nonceInString. i had successfully encrypted and decrypted those. then i split the decrypted data. it was done, too. i want to display the decrypted data in order. something like this. userneme: sebastian password: harrypotter nonce value: sdgvay1saq3qsd5vc6dger9wqktue2tz* i tried the following code, but it didn't display like i wish to. pls help. thanks a lot in advance. String codeWord = username + ";" + password + ";" + nonceInString; String encryptedData = aesEncryptDecrypt.encrypt(codeWord); String decryptedData = aesEncryptDecrypt.decrypt(encryptedData); String[] splits = decryptedData.split(";"); String[] variables = {"username", "password", "nonce value"}; for (String data : variables){ for (String item : splits){ System.out.println( data + ": "+ item); } }

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• C#, AES encryption check!

  - by Data-Base

  I have this code for AES encryption, can some one verify that this code is good and not wrong? it works fine, but I'm more concern about the implementation of the algorithm // Plaintext value to be encrypted. //Passphrase from which a pseudo-random password will be derived. //The derived password will be used to generate the encryption key. //Password can be any string. In this example we assume that this passphrase is an ASCII string. //Salt value used along with passphrase to generate password. //Salt can be any string. In this example we assume that salt is an ASCII string. //HashAlgorithm used to generate password. Allowed values are: "MD5" and "SHA1". //SHA1 hashes are a bit slower, but more secure than MD5 hashes. //PasswordIterations used to generate password. One or two iterations should be enough. //InitialVector (or IV). This value is required to encrypt the first block of plaintext data. //For RijndaelManaged class IV must be exactly 16 ASCII characters long. //KeySize. Allowed values are: 128, 192, and 256. //Longer keys are more secure than shorter keys. //Encrypted value formatted as a base64-encoded string. public static string Encrypt(string PlainText, string Password, string Salt, string HashAlgorithm, int PasswordIterations, string InitialVector, int KeySize) { byte[] InitialVectorBytes = Encoding.ASCII.GetBytes(InitialVector); byte[] SaltValueBytes = Encoding.ASCII.GetBytes(Salt); byte[] PlainTextBytes = Encoding.UTF8.GetBytes(PlainText); PasswordDeriveBytes DerivedPassword = new PasswordDeriveBytes(Password, SaltValueBytes, HashAlgorithm, PasswordIterations); byte[] KeyBytes = DerivedPassword.GetBytes(KeySize / 8); RijndaelManaged SymmetricKey = new RijndaelManaged(); SymmetricKey.Mode = CipherMode.CBC; ICryptoTransform Encryptor = SymmetricKey.CreateEncryptor(KeyBytes, InitialVectorBytes); MemoryStream MemStream = new MemoryStream(); CryptoStream CryptoStream = new CryptoStream(MemStream, Encryptor, CryptoStreamMode.Write); CryptoStream.Write(PlainTextBytes, 0, PlainTextBytes.Length); CryptoStream.FlushFinalBlock(); byte[] CipherTextBytes = MemStream.ToArray(); MemStream.Close(); CryptoStream.Close(); return Convert.ToBase64String(CipherTextBytes); } public static string Decrypt(string CipherText, string Password, string Salt, string HashAlgorithm, int PasswordIterations, string InitialVector, int KeySize) { byte[] InitialVectorBytes = Encoding.ASCII.GetBytes(InitialVector); byte[] SaltValueBytes = Encoding.ASCII.GetBytes(Salt); byte[] CipherTextBytes = Convert.FromBase64String(CipherText); PasswordDeriveBytes DerivedPassword = new PasswordDeriveBytes(Password, SaltValueBytes, HashAlgorithm, PasswordIterations); byte[] KeyBytes = DerivedPassword.GetBytes(KeySize / 8); RijndaelManaged SymmetricKey = new RijndaelManaged(); SymmetricKey.Mode = CipherMode.CBC; ICryptoTransform Decryptor = SymmetricKey.CreateDecryptor(KeyBytes, InitialVectorBytes); MemoryStream MemStream = new MemoryStream(CipherTextBytes); CryptoStream cryptoStream = new CryptoStream(MemStream, Decryptor, CryptoStreamMode.Read); byte[] PlainTextBytes = new byte[CipherTextBytes.Length]; int ByteCount = cryptoStream.Read(PlainTextBytes, 0, PlainTextBytes.Length); MemStream.Close(); cryptoStream.Close(); return Encoding.UTF8.GetString(PlainTextBytes, 0, ByteCount); } Thank you

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• Total Order between !different! volatile variables?

  - by andreas

  Hi all, Consider the following Java code: volatile boolean v1 = false; volatile boolean v2 = false; //Thread A v1 = true; if (v2) System.out.println("v2 was true"); //Thread B v2 = true; if (v1) System.out.println("v1 was true"); If there was a globally visible total order for volatile accesses then at least one println would always be reached. Is that actually guaranteed by the Java Standard? Or is an execution like this possible: A: v1 = true; B: v2 = true; A: read v2 = false; B: read v1 = false; A: v2 = true becomes visible (after the if) B: v1 = true becomes visible (after the if) I could only find statements about accesses to the same volatile variable in the Standard (but I might be missing something). "A write to a volatile variable (§8.3.1.4) v synchronizes-with all subsequent reads of v by any thread (where subsequent is defined according to the synchronization order)." http://java.sun.com/docs/books/jls/third_edition/html/memory.html#17.4.4 Thanks!

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• Can I store SQL Server sort order in a variable?

  - by Steve Weet

  I have the following SQL within a stored procedure. Is there a way to remove the IF statement and pass the 'ASC'/'DESC' option as a variable? I know I could do the query a number of different ways, or return a table and sort it externally etc. I would just like to know if I can avoid duplicating the CASE statement. IF @sortOrder = 'Desc' BEGIN SELECT * FROM #t_results ORDER BY CASE WHEN @OrderBy = 'surname' THEN surname END DESC, CASE WHEN @OrderBy = 'forename' THEN forename END DESC, CASE WHEN @OrderBy = 'fullName' THEN fullName END DESC, CASE WHEN @OrderBy = 'userId' THEN userId END DESC, CASE WHEN @OrderBy = 'MobileNumber' THEN MSISDN END DESC, CASE WHEN @OrderBy = 'DeviceStatus' THEN DeviceStatus END DESC, CASE WHEN @OrderBy = 'LastPosition' THEN LastPosition END DESC, CASE WHEN @OrderBy = 'LastAlert' THEN LastAlert END DESC, CASE WHEN @OrderBy = 'LastCommunication' THEN LastCommunication END DESC, CASE WHEN @OrderBy = 'LastPreAlert' THEN LastPreAlert END DESC END ELSE BEGIN SELECT * FROM #t_results ORDER BY CASE WHEN @OrderBy = 'surname' THEN surname END DESC, CASE WHEN @OrderBy = 'forename' THEN forename END DESC, CASE WHEN @OrderBy = 'fullName' THEN fullName END DESC, CASE WHEN @OrderBy = 'userId' THEN userId END DESC, CASE WHEN @OrderBy = 'MobileNumber' THEN MSISDN END DESC, CASE WHEN @OrderBy = 'DeviceStatus' THEN DeviceStatus END DESC, CASE WHEN @OrderBy = 'LastPosition' THEN LastPosition END DESC, CASE WHEN @OrderBy = 'LastAlert' THEN LastAlert END DESC, CASE WHEN @OrderBy = 'LastCommunication' THEN LastCommunication END DESC, CASE WHEN @OrderBy = 'LastPreAlert' THEN LastPreAlert END DESC END END

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• LINQ to SQL - Why can't you use a WHERE after an ORDER BY?

  - by MCS

  The following code: // select all orders var orders = from o in FoodOrders where o.STATUS = 1 order by o.ORDER_DATE descending select o; // if customer id is specified, only select orders from specific customer if (customerID!=null) { orders = orders.Where(o => customerID.Equals(o.CUSTOMER_ID)); } gives me the following error: Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Linq.IOrderedQueryable'. An explicit conversion exists (are you missing a cast?) I fixed the error by doing the sorting at the end: // select all orders var orders = from o in FoodOrders where o.STATUS = 1 select o; // if customer id is specified, only select orders from specific customer if (customerID!=null) { orders = orders.Where(o => customerID.Equals(o.CUSTOMER_ID)); } // I'm forced to do the ordering here orders = orders.OrderBy(o => o.ORDER_DATE).Reverse(); But I'm wondering why is this limitation in place? What's the reason the API was designed in such a way that you can't add a where constraint after using an order by operator?

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• How to replace custom IDs in the order of their appearance with a shell script?

  - by Péter Török

  I have a pair of rather large log files with very similar content, except that some identifiers are different between the two. A couple of examples: UnifiedClassLoader3@19518cc | UnifiedClassLoader3@d0357a JBossRMIClassLoader@13c2d7f | JBossRMIClassLoader@191777e That is, wherever the first file contains UnifiedClassLoader3@19518cc, the second contains UnifiedClassLoader3@d0357a, and so on. I want to replace these with identical IDs so that I can spot the really important differences between the two files. I.e. I want to replace all occurrences of both UnifiedClassLoader3@19518cc in file1 and UnifiedClassLoader3@d0357a in file2 with UnifiedClassLoader3@1; all occurrences of both JBossRMIClassLoader@13c2d7f in file1 and JBossRMIClassLoader@191777e in file2 with JBossRMIClassLoader@2 etc. Using the Cygwin shell, so far I managed to list all different identifiers occurring in one of the files with grep -o -e 'ClassLoader[0-9]*@[0-9a-f][0-9a-f]*' file1.log | sort | uniq However, now the original order is lost, so I don't know which is the pair of which ID in the other file. With grep -n I can get the line number, so the sort would preserve the order of appearance, but then I can't weed out the duplicate occurrences. Unfortunately grep can not print only the first match of a pattern. I figured I could save the list of identifiers produced by the above command into a file, then iterate over the patterns in the file with grep -n | head -n 1, concatenate the results and sort them again. The result would be something like 2 ClassLoader3@19518cc 137 ClassLoader@13c2d7f 563 ClassLoader3@1267649 ... Then I could (either manually or with sed itself) massage this into a sed command like sed -e 's/ClassLoader3@19518cc/ClassLoader3@2/g' -e 's/ClassLoader@13c2d7f/ClassLoader@137/g' -e 's/ClassLoader3@1267649/ClassLoader3@563/g' file1.log > file1_processed.log and similarly for file2. However, before I start, I would like to verify that my plan is the simplest possible working solution to this. Is there any flaw in this approach? Is there a simpler way?

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• In C++, what is the scope resolution ("order of precedence") for shadowed variable names?

  - by Emile Cormier

  In C++, what is the scope resolution ("order of precedence") for shadowed variable names? I can't seem to find a concise answer online. For example: #include <iostream> int shadowed = 1; struct Foo { Foo() : shadowed(2) {} void bar(int shadowed = 3) { std::cout << shadowed << std::endl; // What does this output? { int shadowed = 4; std::cout << shadowed << std::endl; // What does this output? } } int shadowed; }; int main() { Foo().bar(); } I can't think of any other scopes where a variable might conflict. Please let me know if I missed one. What is the order of priority for all four shadow variables when inside the bar member function?

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• AES encryption/decryption java bouncy castle explanation?

  - by Programmer0

  Can someone please explain what this program is doing pointing out some of the major points? I'm looking at the code and I'm completely lost. I just need explanation on the encryption/decryption phases. I think it generates an AES 192 key at one point but I'm not 100% sure. I'm not sure what the byte/ivBytes are used for either. import java.security.Key; import javax.crypto.Cipher; import javax.crypto.KeyGenerator; import javax.crypto.spec.IvParameterSpec; public class RandomKey { public static void main(String[] args) throws Exception { byte[] input = new byte[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07 }; byte[] ivBytes = new byte[] { 0x00, 0x00, 0x00, 0x01, 0x04, 0x05, 0x06, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01 }; //initializing a new initialization vector IvParameterSpec ivSpec = new IvParameterSpec(ivBytes); //what does this actually do? Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC"); //what does this do? KeyGenerator generator = KeyGenerator.getInstance("AES","BC"); //I assume this generates a key size of 192 bits generator.init(192); //does this generate a random key? Key encryptKey = generator.generateKey(); System.out.println("input: " +toHex(input)); //encryption phase cipher.init(Cipher.ENCRYPT_MODE, encryptKey, ivSpec); //what is this doing? byte[] cipherText = new byte[cipher.getOutputSize(input.length)]; //what is this doing? int ctLength = cipher.update(input, 0, input.length, cipherText,0); //getting the cipher text length i assume? ctLength += cipher.doFinal (cipherText, ctLength ); System.out.println ("Cipher: " +toHex(cipherText) + " bytes: " + ctLength); //decryption phase cipher.init(Cipher.DECRYPT_MODE, encryptKey, ivSpec); //storing the ciphertext in plaintext i'm assuming? byte[] plainText = new byte[cipher.getOutputSize(ctLength)]; int ptLength = cipher.update(cipherText, 0, ctLength, plainText, 0); //getting plaintextLength i think? ptLength= cipher.doFinal (plainText, ptLength); System.out.println("plain: " + toHex(plainText, ptLength)); } private static String digits = "0123456789abcdef"; public static String toHex(byte[] data, int length) { StringBuffer buf = new StringBuffer(); for (int i=0; i!= length; i++) { int v = data[i] & 0xff; buf.append(digits.charAt(v >>4)); buf.append(digits.charAt(v & 0xf)); } return buf.toString(); } public static String toHex(byte[] data) { return toHex(data, data.length); } }

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• Get Nhibernate entity and complete it from a web service.

  - by Nour Sabouny

  Hi every one. let's say that i have an order system. each "Order" references a "Customer" Object. when i fill the orders list in Data Access Layer, the customer object should be brought from a Customer Web Service "WCF". so i didn't map the Customer property in the Order mapping class, Id(o => o.OrderID).GeneratedBy.Identity(); //References(o => o.Customer).Not.Nullable().Column("CustomerID"); HasMany(o => o.Details).KeyColumn("OrderID").Cascade.AllDeleteOrphan(); Map(c => c.CustomerID).Not.Nullable(); and asked the nhibernate session to get me the orders list. and tried to loop on every order in the list to fill it's customer property, doe's any body have a good idea for this ???? IList<Order> lst = Session.CreateCriteria<Order>().List<Order>(); foreach (Order order in lst) order.Customer = serviceProxy.GetCustomerByID(order.CustomerID);

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• In what order should the Python concepts be explained to absolute beginners?

  - by Tomaž Pisanski

  I am teaching Python to undergraduate math majors. I am interested in the optimal order in which students should be introduced to various Python concepts. In my view, at each stage the students should be able to solve a non-trivial programming problem using only the tools available at that time. Each new tool should enable a simpler solution to a familiar problem. A selection of numerous concepts available in Python is essential in order to keep students focused. They should also motivated and should appreciate each newly mastered tool without too much memorization. Here are some specific questions: For instance, my predecessor introduced lists before strings. I think the opposite is a better solution. Should function definitions be introduced at the very beginning or after mastering basic structured programming ideas, such as decisions (if) and loops (while)? Should sets be introduced before dictionaries? Is it better to introduce reading and writing files early in the course or should one use input and print for most of the course? Any suggestions with explanations are most welcome.

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• row number over text column sort

  - by Marty Trenouth

  I'm having problems with dynamic sorting using ROW Number in SQL Server. I have it working but it's throwing errors on non numeric fields. What do I need to change to get sorts with Alpha Working??? ID Description 5 Test 6 Desert 3 A evil Ive got a Sql Prodcedure CREATE PROCEDURE [CRUDS].[MyTable_Search] -- Add the parameters for the stored procedure here -- Full Parameter List @ID int = NULL, @Description nvarchar(256) = NULL, @StartIndex int = 0, @Count int = null, @Order varchar(128) = 'ID asc' AS BEGIN -- SET NOCOUNT ON added to prevent extra result sets from -- interfering with SELECT statements. SET NOCOUNT ON; -- Insert statements for procedure here Select * from ( Select ROW_NUMBER() OVER (Order By case when @Order = 'ID asc' then [TableName].ID when @Order = 'Description asc' then [TableName].Description end asc, case when @Order = 'ID desc' then [TableName].ID when @Order = 'Description desc' then [TableName].Description end desc ) as row, [TableName].* from [TableName] where (@ID IS NULL OR [TableName].ID = @ID) AND (@Description IS NULL OR [TableName].Description = @Description) ) as a where row > @StartIndex and (@Count is null or row <= @StartIndex + @Count) order by case when @Order = 'ID asc' then a.ID when @Order = 'Description asc' then a.Description end asc, case when @Order = 'ID desc' then a.ID when @Order = 'Description desc' then a.Description end desc END

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• Why some pictures are are crooked aftes using my function?

  - by Miko Kronn

  struct BitmapDataAccessor { private readonly byte[] data; private readonly int[] rowStarts; public readonly int Height; public readonly int Width; public BitmapDataAccessor(byte[] data, int width, int height) { this.data = data; this.Height = height; this.Width = width; rowStarts = new int[height]; for (int y = 0; y < Height; y++) rowStarts[y] = y * width; } public byte this[int x, int y, int color] // Maybe use an enum with Red = 0, Green = 1, and Blue = 2 members? { get { return data[(rowStarts[y] + x) * 3 + color]; } set { data[(rowStarts[y] + x) * 3 + color] = value; } } public byte[] Data { get { return data; } } } public static byte[, ,] Bitmap2Byte(Bitmap obraz) { int h = obraz.Height; int w = obraz.Width; byte[, ,] wynik = new byte[w, h, 3]; BitmapData bd = obraz.LockBits(new Rectangle(0, 0, w, h), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb); int bytes = Math.Abs(bd.Stride) * h; byte[] rgbValues = new byte[bytes]; IntPtr ptr = bd.Scan0; System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, bytes); BitmapDataAccessor bda = new BitmapDataAccessor(rgbValues, w, h); for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { wynik[j, i, 0] = bda[j, i, 2]; wynik[j, i, 1] = bda[j, i, 1]; wynik[j, i, 2] = bda[j, i, 0]; } } obraz.UnlockBits(bd); return wynik; } public static Bitmap Byte2Bitmap(byte[, ,] tablica) { if (tablica.GetLength(2) != 3) { throw new NieprawidlowyWymiarTablicyException(); } int w = tablica.GetLength(0); int h = tablica.GetLength(1); Bitmap obraz = new Bitmap(w, h, PixelFormat.Format24bppRgb); for (int i = 0; i < w; i++) { for (int j = 0; j < h; j++) { Color kol = Color.FromArgb(tablica[i, j, 0], tablica[i, j, 1], tablica[i, j, 2]); obraz.SetPixel(i, j, kol); } } return obraz; } Now, if I do: private void btnLoad_Click(object sender, EventArgs e) { if (dgOpenFile.ShowDialog() == DialogResult.OK) { try { Bitmap img = new Bitmap(dgOpenFile.FileName); byte[, ,] tab = Grafika.Bitmap2Byte(img); picture.Image = Grafika.Byte2Bitmap(tab); picture.Size = img.Size; } catch (Exception ex) { MessageBox.Show(ex.Message); } } } Most of pictures are handled correctly butsome not. Example of picture that doesn't work: It produce following result (this is only fragment of picture) : Why is that?

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• Accessing appropriate array of double arrays in order of last created.

  - by Zach

  I have an array of double arrays, they are within a specified time window (8am-5pm), and are in order of last created over a period of several days. They are all timestamped and as such I have access to all C# DateTime methods. I then have a different iterative function that goes in the same order of the array of double arrays, however it isn't within a specified time window, it's 24/7. I want to access from this iterative function, the appropriate double array from the one within the window. Let's say that it's 4:30PM on DayOfYear 52, I'd like to access the last double array less than or equal to 4:30PM on DayOfYear 52. I'd expect the same double array if the time were 12:30AM on DayOfYear 53. However, if it were 9:00 AM of DayOfYear 53, well then I'd expect it to return something from the DayOfYear 53, less than or equal to 9:00AM. I think you get the idea. So I'm a having a bit of trouble grokking how to do this. Is anyone willing to offer a starting point or how they'd approach it? Edit: It is not a literal double[][], it is exactly as Anthony Pegram says: Dictionary<DateTime, double[]>

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• Using my custom colormap in Java for images

  - by John

  Hi everyone! I've got a question concering a colormapping via index. I tried this code found on http://www.podgoretsky.pri.ee/ftp/Docs/Java/Tricks%20of%20the%20Java%20Programming%20Gurus/ch12.htm // Gradient.java // Imports import java.applet.Applet; import java.awt.; import java.awt.image.; public class Gradient extends Applet { final int colors = 32; final int width = 200; final int height = 200; Image img; public void init() { // Create the color map byte[] rbmap = new byte[colors]; byte[] gmap = new byte[colors]; for (int i = 0; i < colors; i++) gmap[i] = (byte)((i * 255) / (colors - 1)); // Create the color model int bits = (int)Math.ceil(Math.log(colors) / Math.log(2)); IndexColorModel model = new IndexColorModel(bits, colors, rbmap, gmap, rbmap); // Create the pixels int pixels[] = new int[width * height]; int index = 0; for (int y = 0; y < height; y++) for (int x = 0; x < width; x++) pixels[index++] = (x * colors) / width; // Create the image img = createImage(new MemoryImageSource(width, height, model, pixels, 0, width)); } public void paint(Graphics g) { g.drawImage(img, 0, 0, this); } } It worked great but I tried to load a custom image jpeg mapped on my own colormap but it didnt work right. I saw only a bunch of green and blue pixels drawn on a white background. My custom color map method here: public void inintByteArrays() { double[][] c = // basic color map { { 0.0000, 0.0000, 0.5625 }, { 0.0000, 0.0000, 0.6250 }, { 0.0000, 0.0000, 0.6875 }, { 0.0000, 0.0000, 0.6875 }, { 0.0000, 0.0000, 0.7500 }, { 0.0000, 0.0000, 0.8125 }, { 0.0000, 0.0000, 0.8750 }, { 0.0000, 0.0000, 0.9375 }, { 0.0000, 0.0000, 1.0000 }, { 0.0000, 0.0625, 1.0000 }, { 0.0000, 0.1250, 1.0000 }, { 0.0000, 0.1875, 1.0000 }, { 0.0000, 0.2500, 1.0000 }, { 0.0000, 0.3125, 1.0000 }, { 0.0000, 0.3750, 1.0000 }, { 0.0000, 0.4375, 1.0000 }, { 0.0000, 0.5000, 1.0000 }, { 0.0000, 0.5625, 1.0000 }, { 0.0000, 0.6250, 1.0000 }, { 0.0000, 0.6875, 1.0000 }, { 0.0000, 0.7500, 1.0000 }, { 0.0000, 0.8125, 1.0000 }, { 0.0000, 0.8750, 1.0000 }, { 0.0000, 0.9375, 1.0000 }, { 0.0000, 1.0000, 1.0000 }, { 0.0625, 1.0000, 0.9375 }, { 0.1250, 1.0000, 0.8750 }, { 0.1875, 1.0000, 0.8125 }, { 0.2500, 1.0000, 0.7500 }, { 0.3125, 1.0000, 0.6875 }, { 0.3750, 1.0000, 0.6250 }, { 0.4375, 1.0000, 0.5625 }, { 0.5000, 1.0000, 0.5000 }, { 0.5625, 1.0000, 0.4375 }, { 0.6250, 1.0000, 0.3750 }, { 0.6875, 1.0000, 0.3125 }, { 0.7500, 1.0000, 0.2500 }, { 0.8125, 1.0000, 0.1875 }, { 0.8750, 1.0000, 0.1250 }, { 0.9375, 1.0000, 0.0625 }, { 1.0000, 1.0000, 0.0000 }, { 1.0000, 0.9375, 0.0000 }, { 1.0000, 0.8750, 0.0000 }, { 1.0000, 0.8125, 0.0000 }, { 1.0000, 0.7500, 0.0000 }, { 1.0000, 0.6875, 0.0000 }, { 1.0000, 0.6250, 0.0000 }, { 1.0000, 0.5625, 0.0000 }, { 1.0000, 0.5000, 0.0000 }, { 1.0000, 0.4375, 0.0000 }, { 1.0000, 0.3750, 0.0000 }, { 1.0000, 0.3125, 0.0000 }, { 1.0000, 0.2500, 0.0000 }, { 1.0000, 0.1875, 0.0000 }, { 1.0000, 0.1250, 0.0000 }, { 1.0000, 0.0625, 0.0000 }, { 1.0000, 0.0000, 0.0000 }, { 0.9375, 0.0000, 0.0000 }, { 0.8750, 0.0000, 0.0000 }, { 0.8125, 0.0000, 0.0000 }, { 0.7500, 0.0000, 0.0000 }, { 0.6875, 0.0000, 0.0000 }, { 0.6250, 0.0000, 0.0000 }, { 0.5625, 0.0000, 0.0000 }, { 0.5000, 0.0000, 0.0000 } }; for (int i = 0; i < c.length; i++) { for (int j = 0; j < c[i].length; j++) { if (j == 0) r[i] = (byte) ((byte) c[i][j]*255); if (j == 1) g[i] = (byte) ((byte) c[i][j]*255); if (j == 2) b[i] = (byte) ((byte) c[i][j]*255); } } My question is how I can use my colormap for any image I want to load and map in the right way. Thank you very much! Greetings, protein1.

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