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  • Is there any benefit to my rather quirky character sizing convention?

    - by Paul Alan Taylor
    I love things that are a power of 2. I celebrated my 32nd birthday knowing it was the last time in 32 years I'd be able to claim that my age was a power of 2. I'm obsessed. It's like being some Z-list Batman villain, except without the colourful adventures and a face full of batarangs. I ensure that all my enum values are powers of 2, if only for future bitwise operations, and I'm reasonably assured that there is some purpose (even if latent) for doing it. Where I'm less sure, is in how I define the lengths of database fields. Again, I can't help it. Everything ends up being a power of 2. CREATE TABLE Person ( PersonID int IDENTITY PRIMARY KEY ,Firstname varchar(64) ,Surname varchar(128) ) Can any SQL super-boffins who know about the internals of how stuff is stored and retrieved tell me whether there is any benefit to my inexplicable obsession? Is it more efficient to size character fields this way? Can anyone pop in with an "actually, what you're doing works because ....."? I suspect I'm just getting crazier in my older age, but it'd be nice to know that there is some method to my madness.

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  • Java: what is the class for the isBinary-method?

    - by HH
    I am accustomed to java.io.* and java.util.* but not to the tree: com.starbase.util Class FileUtils java.lang.Object | +--com.starbase.util.FileUtils Source. So which class should I import to use the isBinary-method? Do I do "import java.lang.Object;" or "import java.lang.Object.com.starbase.util.FileUtils;"?

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  • What is the fastest way to do division in C for 8bit MCUs?

    - by Jordan S
    I am working on the firmware for a device that uses an 8bit mcu (8051 architecture). I am using SDCC (Small Device C Compiler). I have a function that I use to set the speed of a stepper motor that my circuit is driving. The speed is set by loading a desired value into the reload register for a timer. I have a variable, MotorSpeed that is in the range of 0 to 1200 which represents pulses per second to the motor. My function to convert MotorSpeed to the correct 16bit reload value is shown below. I know that float point operations are pretty slow and I am wondering if there is a faster way of doing this... void SetSpeed() { float t = MotorSpeed; unsigned int j = 0; t = 1/t ; t = t / 0.000001; j = MaxInt - t; TMR3RL = j; // Set reload register for desired freq return; }

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  • Non standard interaction among two tables to avoid very large merge

    - by riko
    Suppose I have two tables A and B. Table A has a multi-level index (a, b) and one column (ts). b determines univocally ts. A = pd.DataFrame( [('a', 'x', 4), ('a', 'y', 6), ('a', 'z', 5), ('b', 'x', 4), ('b', 'z', 5), ('c', 'y', 6)], columns=['a', 'b', 'ts']).set_index(['a', 'b']) AA = A.reset_index() Table B is another one-column (ts) table with non-unique index (a). The ts's are sorted "inside" each group, i.e., B.ix[x] is sorted for each x. Moreover, there is always a value in B.ix[x] that is greater than or equal to the values in A. B = pd.DataFrame( dict(a=list('aaaaabbcccccc'), ts=[1, 2, 4, 5, 7, 7, 8, 1, 2, 4, 5, 8, 9])).set_index('a') The semantics in this is that B contains observations of occurrences of an event of type indicated by the index. I would like to find from B the timestamp of the first occurrence of each event type after the timestamp specified in A for each value of b. In other words, I would like to get a table with the same shape of A, that instead of ts contains the "minimum value occurring after ts" as specified by table B. So, my goal would be: C: ('a', 'x') 4 ('a', 'y') 7 ('a', 'z') 5 ('b', 'x') 7 ('b', 'z') 7 ('c', 'y') 8 I have some working code, but is terribly slow. C = AA.apply(lambda row: ( row[0], row[1], B.ix[row[0]].irow(np.searchsorted(B.ts[row[0]], row[2]))), axis=1).set_index(['a', 'b']) Profiling shows the culprit is obviously B.ix[row[0]].irow(np.searchsorted(B.ts[row[0]], row[2]))). However, standard solutions using merge/join would take too much RAM in the long run. Consider that now I have 1000 a's, assume constant the average number of b's per a (probably 100-200), and consider that the number of observations per a is probably in the order of 300. In production I will have 1000 more a's. 1,000,000 x 200 x 300 = 60,000,000,000 rows may be a bit too much to keep in RAM, especially considering that the data I need is perfectly described by a C like the one I discussed above. How would I improve the performance?

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  • binary_search not working for a vector<string>

    - by VaioIsBorn
    #include <iostream> #include <string> #include <vector> #include <algorithm> using namespace std; int main(void) { string temp; vector<string> encrypt, decrypt; int i,n, co=0; cin >> n; for(i=0;i<n;i++) { cin >> temp; encrypt.push_back(temp); } for(i=0;i<n;i++) { cin >> temp; decrypt.push_back(temp); } for(i=0;i<n;i++) { temp = encrypt[i]; if((binary_search(decrypt.begin(), decrypt.end(), temp)) == true) ++co; } cout << co << endl; return 0; } It reads two equal lists of strings and should print out how many of the words in the first list are also found in the second list, simple. Not giving me the expexted results and i think the problem is in binary_search. Can you tell me why ?

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  • Right rotate of tree in Haskell: how is it work?

    - by Roman
    I don't know haskell syntax, but I know some FP concepts (like algebraic data types, pattern matching, higher-order functions ect). Can someone explain please, what does this code mean: data Tree ? = Leaf ? | Fork ? (Tree ?) (Tree ?) rotateR tree = case tree of Fork q (Fork p a b) c -> Fork p a (Fork q b c) As I understand, first line is something like Tree-type declaration (but I don't understand it exactly). Second line includes pattern matching (I don't understand as well why do we need to use pattern matching here). And third line does something absolutely unreadable for non-haskell developer. I've found definition of Fork as fork (f,g) x = (f x, g x) but I can't move further anymore.

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  • Homemade fstat to get file size, always return 0 length.

    - by Fred
    Hello, I am trying to use my own function to get the file size from a file. I'll use this to allocate memory for a data structure to hold the information on the file. The file size function looks like this: long fileSize(FILE *fp){ long start; fflush(fp); rewind(fp); start = ftell(fp); return (fseek(fp, 0L, SEEK_END) - start); } Any ideas what I'm doing wrong here?

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  • iPhone SDK - How is data shared in a unversal app

    - by norskben
    Stack overflow I want to make a universal version of my app available, but I am wondering how is data managed between the iPad and the iPhone versions? -Are they completely independent? or if I have a plist in the iPad app, does it also appear in the iPhone app. If so, is there any syncing etc etc. I have a few months experience with single iPad or iPhone apps, but never a universal. Thanks again.

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  • make tree in scheme

    - by ???
    (define (entry tree) (car tree)) (define (left-branch tree) (cadr tree)) (define (right-branch tree) (caddr tree)) (define (make-tree entry left right) (list entry left right)) (define (mktree order items_list) (cond ((= (length items_list) 1) (make-tree (car items_list) '() '())) (else (insert2 order (car items_list) (mktree order (cdr items_list)))))) (define (insert2 order x t) (cond ((null? t) (make-tree x '() '())) ((order x (entry t)) (make-tree (entry t) (insert2 order x (left-branch t)) (right-branch t))) ((order (entry t) x ) (make-tree (entry t) (left-branch t) (insert2 order x (right-branch t)))) (else t))) The result is: (mktree (lambda (x y) (< x y)) (list 7 3 5 1 9 11)) (11 (9 (1 () (5 (3 () ()) (7 () ()))) ()) ()) But I'm trying to get: (7 (3 (1 () ()) (5 () ())) (9 () (11 () ()))) Where is the problem?

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  • How can I access the sign bit of a number in C++?

    - by Keand64
    I want to be able to access the sign bit of a number in C++. My current code looks something like this: int sign bit = number >> 31; That appears to work, giving me 0 for positive numbers and -1 for negative numbers. However, I don't see how I get -1 for negative numbers: if 12 is 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 1100 then -12 is 1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 0011 and shifting it 31 bits would make 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0001 which is 1, not -1, so why do I get -1 when I shift it?

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  • Execute a dll function in ASP.Net Bin not working, II7.

    - by Wayne Lo
    I am developing a remote control application where a client (aspx page in a browser) can request a server to "launch a notepad" (for testing purpose, for real life, turning off a light bulb, etc). So I created a dll with a simple function for launching the notepad (on the server side) and dropped this dll in the root bin folder. It worked fine when the aspx page is running under ASP.NET development server (launched from Visual Studio). But when I tested the same aspx page under a FireFox browser, it did not work (launch the notepad) even though it did call for the same function (I stepped through in debugger). Is this a permission issue? How do I set this up in IIS manager, or even better in web.config? Please help.

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  • IndexOutOfRangeException when a stream is a multiple of the buffer size

    - by dnord
    I don't have a lot of experience with streams and buffers, but I'm having to do it for a project, and I'm stuck on an exception being thrown when the stream I'm reading is a multiple of the buffer size I've chosen. Let me show you: My code starts by reading bufferSize (100, let's say) bytes from the stream: numberOfBytesRead = DataReader.GetBytes(0, index, output, 0, bufferSize); Then, I loop through a while loop: while (numberOfBytesRead == bufferSize) { BufferWriter.Write(output); BufferWriter.Flush(); index += bufferSize; numberOfBytesRead = DataReader.GetBytes(0, index, output, 0, bufferSize); } ... and, once we get to a non-bufferSize read, we know we've hit the end of the stream and can move on. But if the bufferSize is 100, and the stream is 200, we'll read positions 0-99, 100-199, and then the attempt to read 200-299 errors out. I'd like it if it returned 0, but it throws an error. What I'm doing to handle that is, well, a try-catch: catch (System.IndexOutOfRangeException) numberOfBytesRead = 0; ...which ends the loop, and successfully finishes the thing, but we all know I don't want to control code flow with error handling. Is there a better (more standard?) way to handle stream reading when the stream length is unknown? This seems like a small wrinkle in a fairly reasonable strategy for reading streams, but I just don't know if I've got it wrong or what. The specifics of this (which I've cleaned up a little bit for posting) are a MySqlDataReader hitting a LARGEBLOB column. It's working whenever the buffer is larger than the number of returned bytes, or when the number of returned bytes is not a multiple of bufferSize. Because we don't, in that case, throw an IndexOutOfRangeException.

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  • C++ vector and segmentation faults

    - by Headspin
    I am working on a simple mathematical parser. Something that just reads number = 1 + 2; I have a vector containing these tokens. They store a type and string value of the character. I am trying to step through the vector to build an AST of these tokens, and I keep getting segmentation faults, even when I am under the impression my code should prevent this from happening. Here is the bit of code that builds the AST: struct ASTGen { const vector<Token> &Tokens; unsigned int size, pointer; ASTGen(const vector<Token> &t) : Tokens(t), pointer(0) { size = Tokens.size() - 1; } unsigned int next() { return pointer + 1; } Node* Statement() { if(next() <= size) { switch(Tokens[next()].type) { case EQUALS : Node* n = Assignment_Expr(); return n; } } advance(); } void advance() { if(next() <= size) ++pointer; } Node* Assignment_Expr() { Node* lnode = new Node(Tokens[pointer], NULL, NULL); advance(); Node* n = new Node(Tokens[pointer], lnode, Expression()); return n; } Node* Expression() { if(next() <= size) { advance(); if(Tokens[next()].type == SEMICOLON) { Node* n = new Node(Tokens[pointer], NULL, NULL); return n; } if(Tokens[next()].type == PLUS) { Node* lnode = new Node(Tokens[pointer], NULL, NULL); advance(); Node* n = new Node(Tokens[pointer], lnode, Expression()); return n; } } } }; ... ASTGen AST(Tokens); Node* Tree = AST.Statement(); cout << Tree->Right->Data.svalue << endl; I can access Tree->Data.svalue and get the = Node's token info, so I know that node is getting spawned, and I can also get Tree->Left->Data.svalue and get the variable to the left of the = I have re-written it many times trying out different methods for stepping through the vector, but I always get a segmentation fault when I try to access the = right node (which should be the + node) Any help would be greatly appreciated.

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  • Balanced Search Tree Query, Asymtotic Analysis..

    - by AGeek
    Hi, The situation is as follows:- We have n number and we have print them in sorted order. We have access to balanced dictionary data structure, which supports the operations serach, insert, delete, minimum, maximum each in O(log n) time. We want to retrieve the numbers in sorted order in O(n log n) time using only the insert and in-order traversal. The answer to this is:- Sort() initialize(t) while(not EOF) read(x) insert(x,t); Traverse(t); Now the query is if we read the elements in time "n" and then traverse the elements in "log n"(in-order traversal) time,, then the total time for this algorithm (n+logn)time, according to me.. Please explain the follow up of this algorithm for the time calculation.. How it will sort the list in O(nlogn) time?? Thanks.

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  • Worst Case number of rotations for BST to AVL algorithm?

    - by spacker_lechuck
    I have a basic algorithm below and I know that the worst case input BST is one that has degenerated to a linked list from inserts to only one side. How would I compute the worst case complexity in terms of number of rotations for this BST to AVL conversion algorithm? IF tree is right heavy { IF tree's right subtree is left heavy { Perform Double Left rotation } ELSE { Perform Single Left rotation } } ELSE IF tree is left heavy { IF tree's left subtree is right heavy { Perform Double Right rotation } ELSE { Perform Single Right rotation } }

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  • How to take a collection of bytes and pull typed values out of it?

    - by Pat
    Say I have a collection of bytes var bytes = new byte[] {0, 1, 2, 3, 4, 5, 6, 7}; and I want to pull out a defined value from the bytes as a managed type, e.g. a ushort. What is a simple way to define what types reside at what location in the collection and pull out those values? One (ugly) way is to use System.BitConverter and a Queue or byte[] with an index and simply iterate through, e.g.: int index = 0; ushort first = System.BitConverter.ToUint16(bytes, index); index += 2; // size of a ushort int second = System.BitConverter.ToInt32(bytes, index); index += 4; ... This method gets very, very tedious when you deal with a lot of these structures! I know that there is the System.Runtime.InteropServices.StructLayoutAttribute which allows me to define the locations of types inside a struct or class, but there doesn't seem to be a way to import the collection of bytes into that struct. If I could somehow overlay the struct on the collection of bytes and pull out the values, that would be ideal. E.g. Foo foo = (Foo)bytes; // doesn't work because I'd need to implement the implicit operator ushort first = foo.first; int second = foo.second; ... [StructLayout(LayoutKind.Explicit, Size=FOO_SIZE)] public struct Foo { [FieldOffset(0)] public ushort first; [FieldOffset(2)] public int second; } Any thoughts on how to achieve this?

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  • Bitwise operations in BC?

    - by user355926
    $ bc BC> ibase=2 BC> 110&101 // wanna get 100 (standar_in) 8: syntax error Wikipedia informs that the ops are "|, & and ^". It may be that they work only in certain BC-types or I misread something.

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  • why IEEE floating point number calculate exponent using a biased form?

    - by lenatis
    let's say, for the float type in c, according to the IEEE floating point specification, there are 8-bit used for the fraction filed, and it is calculated as first taken these 8-bit and translated it into an unsigned number, and then minus the BIASE, which is 2^7 - 1 = 127, and the result is an exponent ranges from -127 to 128, inclusive. But why can't we just treat these 8-bit pattern as a signed number, since the resulting range is [-128,127], which is almost the same as the previous one.

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  • Delete an object from a tree

    - by mqpasta
    I have a Find function in order to find an element from a BST private Node Find(ref Node n, int e) { if (n == null) return null; if (n.Element == e) return n; if (e > n.Element) return Find(ref n.Right, e); else return Find(ref n.Left, e); } and I use following code in order to get a node and then set this node to null. Node x = bsTree.Find(1); x = null; bsTree.Print(); supposedly, this node should be deleted from Tree as it is set to null but it still exists in tree. I had done this before but this time missing something and no idea what.

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  • iPhone - How to use #define in Universal app

    - by Satyam svv
    I'm creating universal app that runs oniphone and ipad. I'm using #define to create CGRect. And I want to use two different #define - one for iPhone and one for iPad. How can I declare them so that correct one will be picked by universal app.......... I think I've to update little more description to avoid confusion. I've a WPConstants.h file where I'm declaring all the #define as below #define PUZZLE_TOPVIEW_RECT CGRectMake(0, 0, 480, 100) #define PUZZLE_MIDDLEVIEW_RECT CGRectMake(0, 100, 480, 100) #define PUZZLE_BOTTOMVIEW_RECT CGRectMake(0, 200, 480, 100) The above ones are for iphone. Similarly for iPad I want to have different #define How can I proceed further?

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  • Count in base 2, 3, 4 etc in Java and output all permutations

    - by tree-hacker
    I want to write a function in Java that takes as input an integer and outputs every possible permutation of numbers up to that integer. For example: f(1) 0 f(2) should output: 00 01 10 11 f(3) should output: 000 001 002 010 011 012 020 021 022 100 .... 220 221 222 That is it should output all 27 permutations of the digits of the numbers 0, 1, 2. f(4) should output 0000 0001 0002 0003 0010 ... 3330 3331 3332 3333 f(4) should output 00000 00001 ... 44443 44444 I have been trying to solve this problem but cannot seem to work out how to do it and keep getting confused by how many loops I need. Does anyone know how to solve this problem? Thanks in advance.

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