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• iPhone OS: Strategies for high density image work

  - by Jasconius

  I have a project that is coming around the bend this summer that is going to involve, potentially, an extremely high volume of image data for display. We are talking hundreds of 640x480-ish images in a given application session (scaled to a smaller resolution when displayed), and handfuls of very large (1280x1024 or higher) images at a time. I've already done some preliminary work and I've found that the typical 640x480ish image is just a shade under 1MB in memory when placed into a UIImageView and displayed... but the very large images can be a whopping 5+ MB's in some cases. This project is actually be targeted at the iPad, which, in my Instruments tests seems to cap out at about 80-100MB's of addressable physical memory. Details aside, I need to start thinking of how to move huge volumes of image data between virtual and physical memory while preserving the fluidity and responsiveness of the application, which will be high visibility. I'm probably on the higher ends of intermediate at Objective-C... so I am looking for some solid articles and advice on the following: 1) Responsible management of UIImage and UIImageView in the name of conserving physical RAM 2) Merits of using CGImage over UIImage, particularly for the huge images, and if there will be any performance gain 3) Anything dealing with memory paging particularly as it pertains to images I will epilogue by saying that the numbers I have above maybe off by about 10 or 15%. Images may or may not end up being bundled into the actual app itself as opposed to being loaded in from an external server.

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• Parsing basic math equations for children's educational software?

  - by Simucal

  Inspired by a recent TED talk, I want to write a small piece of educational software. The researcher created little miniature computers in the shape of blocks called "Siftables". [David Merril, inventor - with Siftables in the background.] There were many applications he used the blocks in but my favorite was when each block was a number or basic operation symbol. You could then re-arrange the blocks of numbers or operation symbols in a line, and it would display an answer on another siftable block. So, I've decided I wanted to implemented a software version of "Math Siftables" on a limited scale as my final project for a CS course I'm taking. What is the generally accepted way for parsing and interpreting a string of math expressions, and if they are valid, perform the operation? Is this a case where I should implement a full parser/lexer? I would imagine interpreting basic math expressions would be a semi-common problem in computer science so I'm looking for the right way to approach this. For example, if my Math Siftable blocks where arranged like: [1] [+] [2] This would be a valid sequence and I would perform the necessary operation to arrive at "3". However, if the child were to drag several operation blocks together such as: [2] [\] [\] [5] It would obviously be invalid. Ultimately, I want to be able to parse and interpret any number of chains of operations with the blocks that the user can drag together. Can anyone explain to me or point me to resources for parsing basic math expressions? I'd prefer as much of a language agnostic answer as possible.

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• How do you read a file line by line in your language of choice?

  - by Jon Ericson

  I got inspired to try out Haskell again based on a recent answer. My big block is that reading a file line by line (a task made simple in languages such as Perl) seems complicated in a functional language. How do you read a file line by line in your favorite language? So that we are comparing apples to other types of apples, please write a program that numbers the lines of the input file. So if your input is: Line the first. Next line. End of communication. The output would look like: 1 Line the first. 2 Next line. 3 End of communication. I will post my Haskell program as an example. Ken commented that this question does not specify how errors should be handled. I'm not overly concerned about it because: Most answers did the obvious thing and read from stdin and wrote to stdout. The nice thing is that it puts the onus on the user to redirect those streams the way they want. So if stdin is redirected from a non-existent file, the shell will take care of reporting the error, for instance. The question is more aimed at how a language does IO than how it handles exceptions. But if necessary error handling is missing in an answer, feel free to either edit the code to fix it or make a note in the comments.

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• Catching 'Last Record' in Coldfusion for IE javascript bug

  - by Simon Hume

  I'm using ColdFusion to pull UK postcodes into an array for display on a Google Map. This happens dynamically from a SQL database, so the numbers can range from 1 to 100+ the script works great, however, in IE (groan) it decides to display one point way off line, over in California somewhere. I fixed this issue in a previous webapp, this was due to the comma between each array item still being present at the end. Works fine in Firefox, Safari etc, but not IE. But, that one was using a set 10 records, so was easy to fix. I just need a little if statement to wrap around my comma to hide it when it hits the last record. I can't seem to get it right. Any tips/suggestions? here is the line of code in question: var address = [<cfloop query="getApplicant"><cfif getApplicant.dbHomePostCode GT ""><cfoutput>'#getApplicant.dbHomePostCode#',</cfoutput></cfif> </cfloop>]; Hopefully someone can help with this rather simple request. I'm just having a bad day at the office!

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• Use AJAX to reload captcha

  - by arik-so

  Hello! This question may have been asked already - but unfortunately, I could not find any satisfactory answers. I will just ask it for my concrete case and ask the admins not to delete the question for at least a few days so I can try it out... I have a page. It uses a captcha. Like so: <?php session_start(); // the captcha saves the md5 into the session ?> <img src="captcha.php" onclick="this.src = this.src" /> That was my first code. It did not work, because the browser condsidered it useless to reload an image if the source is the same. My current solution is to pass a get parameter: onclick="this.src = 'captcha.php?randomNumber='+ranNum" The JavaScript variable var ranNum is generated randomly every time the onclick event fires. It works fine, still, I don't like the possibility, if the - though improbable - case of two numbers being the same twice in a row. Although the random number varies between -50,000 and 50,000 - I still do not like it. And I don't think the method is right. I would like to know the 'righter' method, by means of AJAX. I know it's possible. I hope you know how it's possible ^^ In that case, please show me. Thanks in advance! By the way - if I spell cap(t)cha differently, never mind, the reference to the PHP file is right in my code: I use randomImage.php

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• C++ LPTSTR to int (but memory overwrite problem using atoi)

  - by Dexter

  I have the following code, m_edit is a MFC CEdit (I know I would never use MFC but project demanded it). It's a simple loop, that gets the text from a text edit, converts it to integer after getting the first line, then stores it in m_y vector. LPTSTR szTemp; vector<int> m_y; for(int i = 0; i < m_edit->GetLineCount(); i++){ szTemp = s_y.GetBuffer(0); m_edit->GetLine(i, szTemp); // get line text store in szTemp y = atoi(szTemp); m_y.push_back(y); szTemp = ""; y = 0; } IMPORTANT EXAMPLE: So let's say the CEdit has 6 numbers: 0 5 2 5 18 6 If you use Visual Studio's debugger you will notice an anomaly!! Here's what it shows: y = 0 y = 5 y = 2 y = 5 y = 18 y = 68 Do you see that? szTemp when inserted into atoi, it returns the number 6, but concatenates the 2nd digit of the last number!!! This is why I did szTemp = "";, but the problem persists. Also, let's say the last number was 17 (not 18), then this time debugger would say y = 67, so it is definitely this problem. However, Visual Studio debugger, when you hover over szTemp during this iteration, it says '6' <--- not '68' inside szTemp. So somehow atoi is ruining it. Am I suppose to concatenate a \0 into szTemp before putting it into atoi? How do I solve this easily?

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• SVN authz, path-based authentication woes

  - by Ronny

  [groups] developer = a,b,c doc = r,x [/doc] @doc = rw @developer = rw [/] @developer = rw * = If now a member of the group doc tries to check out the documentation, it does not work. I want members of doc just to be able to check out the sub-dir doc, anything else is forbidden. Any ideas howto achieve this? kind regards ronny [update] client: svn, version 1.5.4 (r33841) server: svn, Version 1.4.6 (r28521) access via svn+ssh:/user@host/fullpath-to-repos 1 perfectly works for two years 2 might be - see version numbers above (I'll contant our admin, immediatelly) 3 no? just ssh 4 nope 5 nope [update] using client version svn 1.4.6 (r28521) does not work either - same errors I use plain command line access. svn co svn+ssh://.... [update] server:Linux 2.6.16.60-0.39.3-default9 i686 athlon i386 GNU/Linux - suse 10? or something like that I think client: Kubuntu 9.04 connection via OpenSSH SSH client the server rejects svn:// connections from localhost - any connection --- gotta try it with a copy at home time soon [update 4] * this is not my own server, I cannot do what I want with it. It is a very old server 10 years at least running, with hundreds of users. Standard things should work. correct me if I am missing something. [update 5] believe it or not. I was using the wrong path and now everything works perfectly well, I am sorry to have wasted your time. I'll give the bounty to FoxyBOA for his efford.

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• How can I search an XML file without a dynamic language?

  - by jeph perro

  Let me try to explain my situation: We are using a CMS which 'bakes' a website, and you publish it to a webserver. The published site contains only static HTML ( or XML ) pages ( generated from the content in the CMS database ). I imported an XML file with the names and phone numbers from the company phone directory. Using only XSLT, can I create a way to search that directory? For example, if my XML file, directory.xml looks like this: <directory> <person> <fname>Ryan</fname> <lname>Purple</lname> <phone>887 778 5544</phone> </person> <person> <fname>Tanya</fname> <lname>Orange</lname> <phone>887 998 5541</phone> </person> <directory> Can I create a way to search for a person with the last name starting with "Pur" ? Can I pass a parameter to the XSLT? Can I search the XML tree to match the string in the parameter?

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• Issues with reversing bit shifts that roll over the maximum byte size?

  - by Terri

  I have a string of binary numbers that was originally a regular string and will return to a regular string after some bit manipulation. I'm trying to do a simple caesarian shift on the binary string, and it needs to be reversable. I've done this with this method.. public static String cShift(String ptxt, int addFactor) { String ascii = ""; for (int i = 0; i < ptxt.length(); i+=8) { int character = Integer.parseInt(ptxt.substring(i, i+8), 2); byte sum = (byte) (character + addFactor); ascii += (char)sum; } String returnToBinary = convertToBinary(ascii); return returnToBinary; } This works fine in some cases. However, I think when it rolls over being representable by one byte it's irreversable. On the test string "test!22*F ", with an addFactor of 12, the string becomes irreversible. Why is that and how can I stop it?

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• Can't get data with spaces into the database from Ajax POST request

  - by J Jones

  I have a real simple form with a textbox and a button, and my goal is to have an asynchronous request (jQuery: $.ajax) send the text to the server (PHP/mysql a la Joomla) so that it can be added to a database table. Here's the javascript that is sending the data from the client: var value= $('#myvalue').val(); $.ajax( { type: "POST", url: "/administrator/index.php", data: { option: "com_mycomponent", task: "enterValue", thevalue: value, format: "raw"}, dataType: "text", success: reportSavedValue } ); The problem arises when the user enters text with a space in it. The $_POST variable that I receive has all the spaces stripped out, so that if the user enters "This string has spaces", the server gets the value "Thisstringhasspaces". I have been googling around, and have found lots of references that I need to use encodeURIComponent. So I have tried it, but now the value that I get from $_POST is "This20string20has20spaces". So it appears to be encoding it the way I would expect, only to have the percent signs stripped instead of the spaces, and leaving the hex numbers. I'm really confused. It seems that this sort of question is asked and answered everywhere on the web, and everywhere encodeURIComponent is hailed as the silver bullet. But apparently I'm fighting a different breed of lycanthrope. Does anyone have any suggestions?

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• How to Use XSLT to Replace Coordinate Separator With List of Tuples?

  - by kuloch

  I have a space-separated list of coordinate tuples. Each tuple consists of a space-separated list of 2-dimensional coordinates. E.g. "1.1 2.8 1.2 2.9" represents a line from POINT(1.1 2.8) to POINT(1.2 2.9). I need this to instead be "1.1,2.8 1.2,2.9". How would I use XSLT to perform the replacement of space-to-comma between pairs of numbers? I have the "string(gml:LinearRing/gml:posList)". This is being used on a Java Web Service that spits out GML 3.1.1 features with geometries. The service supports optional KML output, by using XSLT to transform the GML document into a KML document (at least, the chunks deemed "important"). I am locked into XSLT 1.0, so regex from XSLT 2.0 is not an option. I am aware that GML uses lat/lon while KML uses lon/lat. That's being handled before XSLT, though it would be nice to have that also done with XSLT.

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• Problem with writing a hexadecimal string

  - by quilby

  Here is my code /* gcc -c -Wall -g main.c gcc -g -lm -o main main.o */ #include <stdlib.h> #include <stdio.h> #include <string.h> void stringToHex(const char* string, char* hex) { int i = 0; for(i = 0; i < strlen(string)/2; i++) { printf("s%x", string[2*i]); //for debugging sprintf(&hex[i], "%x", string[2*i]); printf("h%x\n", hex[i]); //for debugging } } void writeHex(char* hex, int length, FILE* file, long position) { fseek(file, position, SEEK_SET); fwrite(hex, sizeof(char), length, file); } int main(int argc, char** argv) { FILE* pic = fopen("hi.bmp", "w+b"); const char* string = "f2"; char hex[strlen(string)/2]; stringToHex(string, hex); writeHex(hex, strlen(string)/2, pic, 0); fclose(pic); return 0; } I want it to save the hexadecimal number 0xf2 to a file (later I will have to write bigger/longer numbers though). The program prints out - s66h36 And when I use hexedit to view the file I see the number '36' in it. Why is my code not working? Thanks!

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• How can I randomly iterate through a large Range?

  - by void

  I would like to randomly iterate through a range. Each value will be visited only once and all values will eventually be visited. For example: class Array def shuffle ret = dup j = length i = 0 while j > 1 r = i + rand(j) ret[i], ret[r] = ret[r], ret[i] i += 1 j -= 1 end ret end end (0..9).to_a.shuffle.each{|x| f(x)} where f(x) is some function that operates on each value. A Fisher-Yates shuffle is used to efficiently provide random ordering. My problem is that shuffle needs to operate on an array, which is not cool because I am working with astronomically large numbers. Ruby will quickly consume a large amount of RAM trying to create a monstrous array. Imagine replacing (0..9) with (0..99**99). This is also why the following code will not work: tried = {} # store previous attempts bigint = 99**99 bigint.times { x = rand(bigint) redo if tried[x] tried[x] = true f(x) # some function } This code is very naive and quickly runs out of memory as tried obtains more entries. What sort of algorithm can accomplish what I am trying to do? [Edit1]: Why do I want to do this? I'm trying to exhaust the search space of a hash algorithm for a N-length input string looking for partial collisions. Each number I generate is equivalent to a unique input string, entropy and all. Basically, I'm "counting" using a custom alphabet. [Edit2]: This means that f(x) in the above examples is a method that generates a hash and compares it to a constant, target hash for partial collisions. I do not need to store the value of x after I call f(x) so memory should remain constant over time. [Edit3/4/5/6]: Further clarification/fixes.

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• Password Cracking in 2010 and Beyond

  - by mttr

  I have looked a bit into cryptography and related matters during the last couple of days and am pretty confused by now. I have a question about password strength and am hoping that someone can clear up my confusion by sharing how they think through the following questions. I am becoming obsessed about these things, but need to spend my time otherwise :-) Let's assume we have an eight-digit password that consists of upper and lower-case alphabetic characters, numbers and common symbols. This means we have 8^96 ~= 7.2 quadrillion different possible passwords. As I understand there are at least two approaches to breaking this password. One is to try a brute-force attack where we try to guess each possible combination of characters. How many passwords can modern processors (in 2010, Core i7 Extreme for eg) guess per second (how many instructions does a single password guess take and why)? My guess would be that it takes a modern processor in the order of years to break such a password. Another approach would consist of obtaining a hash of my password as stored by operating systems and then search for collisions. Depending on the type of hash used, we might get the password a lot quicker than by the bruteforce attack. A number of questions about this: Is the assertion in the above sentence correct? How do I think about the time it takes to find collisions for MD4, MD5, etc. hashes? Where does my Snow Leopard store my password hash and what hashing algorithm does it use? And finally, regardless of the strength of file encryption using AES-128/256, the weak link is still my en/decryption password used. Even if breaking the ciphered text would take longer than the lifetime of the universe, a brute-force attack on my de/encryption password (guess password, then try to decrypt file, try next password...), might succeed a lot earlier than the end of the universe. Is that correct? I would be very grateful, if people could have mercy on me and help me think through these probably simple questions, so that I can get back to work.

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• Load Spikes on a Apache MySQL Server with Wordpress MU

  - by Vikram Goyal

  Hi there, I am trying to investigate the reasons for some mysterious load spikes on a Linux Apache server (2.2.14) running PHP 5.2.9 on a dedicated server with enough processing power and memory. My primary web application is a Wordpress MU (2.9.2) installation. I have investigated and ruled out DOS attack, MySQL or Apache configuration issues. The log files don't give me anything of interest, except to tell me that there is severe load. The load (which can go up to 100) just seems to come and go. It helps that I have a script that checks every 3 minutes for the load, and restarts Apache. Restarting it helps, and the server comes back, till it happens again. There seems to be no set time frame, or visitor numbers on the site that can trigger this. Even a low number of concurrent visitors (20) can trigger it. I am almost convinced that there is a rewrite loop somewhere that is causing Apache to go mad. Apache is trying to serve something that is causing it to spawn more and more processes till it keels over. My question is: Given that I am convinced that this is a rewrite issue or something similar, how can I try and figure out what the issue is? What should I monitor? Apache logs are voluminous, and not very helpful. Of course, if this is not the issue, then at least knowing what to look for will help me eliminate this as an issue and look for something else. Thanks! Vikram

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• Build number increment not reflected in AssemblyVersion

  - by awshepard

  I've browsed through some of the discussion on auto-incrementing build numbers, but in the impatience of youth decided to roll my own and re-invent the wheel. I know there are probably better ways to go about this (which I'm definitely going to investigate), but my question centers more around the Assembly and/or Version classes. My approach was to write a separate exe (BuildIncrementer) that takes a command line parameter for file name, does a regex match on the contents to grab the [assembly: AssemblyVersion...] string, do the modifications that I want (increment the build number, etc.), then write the contents back to the file. This approach works as-is. The next thing I did was in the project that I wanted to use this on, I set up a pre-build command line that is simply the command to execute that BuildIncrementer.exe on this project's AssemblyInfo.cs file. This too works, updating the assembly info as desired. The problem comes when I run the project, it sends an email containing the current version, obtained with Assembly.GetExecutingAssembly().GetName().Version.ToString(). BUT, the version showing up is the previous version. When my AssemblyInfo.cs says [assembly: AssemblyVersion("1.0.2.49667")], I get sent 1.0.1.45660, which was the previous build. Anyone have any ideas why that might be?

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• What is the Difference between GC.GetTotalMemory(false) and GC.GetTotalMemory(true)

  - by somaraj

  Hi, Could some one tell me the difference between GC.GetTotalMemory(false) and GC.GetTotalMemory(true); I have a small program and when i compared the results the first loop gives an put put < loop count 0 Diff = 32 for GC.GetTotalMemory(true); and < loop count 0 Diff = 0 for GC.GetTotalMemory(false); but shouldnt it be the otherway ? Smilarly rest of the loops prints some numbers ,which are different for both case. what does this number indicate .why is it changing as the loop increase. struct Address { public string Streat; } class Details { public string Name ; public Address address = new Address(); } class emp :IDisposable { public Details objb = new Details(); bool disposed = false; #region IDisposable Members public void Dispose() { Disposing(true); } void Disposing(bool disposing) { if (!disposed) disposed = disposing; objb = null; GC.SuppressFinalize(this); } #endregion } class Program { static void Main(string[] args) { long size1 = GC.GetTotalMemory(false); emp empobj = null; for (int i = 0; i < 200;i++ ) { // using (empobj = new emp()) //------- (1) { empobj = new emp(); //------- (2) empobj.objb.Name = "ssssssssssssssssss"; empobj.objb.address.Streat = "asdfasdfasdfasdf"; } long size2 = GC.GetTotalMemory(false); Console.WriteLine( "loop count " +i + " Diff = " +(size2-size1)); } } } }

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• Collecting high-volume video viewing data

  - by DanK

  I want to add tracking to our Flash-based media player so that we can provide analytics that show what sections of videos are being watched (at the moment, we just register a view when a video starts playing) For example, if a viewer watches the first 30 seconds of a video and then clicks away to something else, we want the data to reflect that. Likewise, if someone watches the first 10 seconds, then scrubs the timeline to the last minute of the video and watches that, we want to register viewing on the parts watched and not the middle section. My first thought was to collect up the viewing data in the player and send it all to the server at the end of a viewing session. Unfortunately, Flash does not seem to have an event that you can hook into when a viewer clicks away from the page the movie is on (probably a good thing - it would be open to abuse) So, it looks like we're going to have to make regular requests to the server as the video is playing. This is obviously going to lead to a high volume of requests when there are large numbers of simultaneous viewers. The simple approach of dumping all these 'heartbeat' events from clients to a database feels like it will quickly become unmanageable so I'm wondering whether I should be taking an approach where viewing sessions are cached in memory and flushed to database when they become inactive (based on a timeout). That way, the data could be stored as time spans rather than individual heartbeats. So, to the question - what is the best way to approach dealing with this kind of high-volume viewing data? Are there any good existing architectures/patterns? Thanks, Dan.

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• How to convert String format dates to Date format dates?

  - by Jani Bela

  I have a string with dates it looks like: "20120316 20120317 20120318" ... I store this dates in this format, but I would like to make a Date array from these numbers with the format 03/16 03/17 03/18 ... So far: String[] DailyDatasOnce2 = DatesOnce.split(" "); DailyDatasOnce = new String[DailyDatasOnce2.length]; for (int i=0;i< (DailyDatasOnce2.length) ;i++){ DailyDatasOnce[i]=DailyDatasOnce2[i]; } datumok = new Date[DailyDatasOnce.length]; for (int i=0;i< (DailyDatasOnce.length) ;i++){ SimpleDateFormat curFormater = new SimpleDateFormat("yyyyMMdd"); java.util.Date dateObj = null; java.util.Date dateObj2 = null; try { dateObj = curFormater.parse(DailyDatasOnce[i]); } catch (ParseException e) { // TODO Auto-generated catch block e.printStackTrace(); } SimpleDateFormat postFormater = new SimpleDateFormat("MM/dd"); String newDateStr = postFormater.format(dateObj); try { dateObj2 = curFormater.parse(newDateStr); } catch (ParseException e) { // TODO Auto-generated catch block e.printStackTrace(); } datumok[i] = dateObj2; } So first I make a string array with the string dates (DailyDatasOnce), maybe that first for loop is useless but i can skip it. Now I make a Date array and I want to put the dates into it. I format the dates to format I want, then I try to convert them to Date format. Until the String newDateStr it is working, I manage to change the type of the date. But I get syntax error: Type mismatch: Cannot convert from java.util.date to java.sql.data. I suspect the problem but if it is not possible, how can i do this?

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• Mouse move panning

  - by Rudy

  Hi all, I'm trying to scroll a series of thumbnails horizontally based on the mouseX position. I can get it to scroll but it's very choppy and for some reason it's not reading my start and end numbers so it will stop scrolling. Can anyone point me in the right direction? Thanks. var thumbBounds:Object = new Object(); thumbBounds = thumbContainer.getBounds(this); thumbContainer.addEventListener(MouseEvent.MOUSE_OVER, setScrolling); private function setScrolling(me:MouseEvent):void { thumbContainer.removeEventListener(MouseEvent.MOUSE_OVER, setScrolling); stage.addEventListener(Event.ENTER_FRAME, scrollThumbs); } private function scrollThumbs(e:Event):void { if(mouseX <= thumbBounds.x || mouseX thumbBounds.width || mouseX < thumbBounds.y || mouseX thumbBounds.height) { thumbContainer.addEventListener(MouseEvent.MOUSE_OVER, setScrolling); stage.removeEventListener(Event.ENTER_FRAME, scrollThumbs); } if(thumbContainer.x = 0) { thumbContainer.x = 0; } if(thumbContainer.x <= -842) { thumbContainer.x = -842; } var xdist:Number = new Number(); xdist = mouseX - 382; thumbContainer.x += Math.round(-xdist / 10); }

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• Google Maps Terms of Service - saving some data to a database

  - by R.M.

  I've read the terms of service, and, from what I understand, I'm not allowed to store any information I retrieve from the Google Maps API. Are there any exceptions to this? More to the point, I'm planning on building an application that shows the user several points of interest (like restaurants, libraries etc) at a certain distance around a location he chooses (it can be in one city or more, depending on the distance he chooses). There are two problems: The first problem is that (at least for my country) the geocoder doesn't locate exact addresses, at best it only locates street names (but completely ignores street numbers) in larger cities. It is even worse for smaller rural areas. So the only way to accurately show the places on the map is by storing their coordinates in the database. Another problem seems to be with calculating distances. To show the points located below a certain distance from the user, it would mean I would have to use GDirections to get all distances between the user's location and the other points, to see which ones to show. That would be really slow for the user (since I also have to set a small delay between requests), and it would also send a pretty large amount of requests to google. Would I be allowed to store those distances in a database? The users would not be able to access a list of all the stored information, they would only see the names of the places, and a map with some markers on it. Thank you.

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• How to convert struct to char array in C

  - by falcojr

  I'm trying to convert a struct to a char array to send over the network. However, I get some weird output from the char array when I do. #include <stdio.h> struct x { int x; } __attribute__((packed)); int main() { struct x a; a.x=127; char *b = (char *)&a; int i; for (i=0; i<4; i++) printf("%02x ", b[i]); printf("\n"); for (i=0; i<4; i++) printf("%d ", b[i]); printf("\n"); return 0; } Here is the output for various values of a.x (on an X86 using gcc): 127: 7f 00 00 00 127 0 0 0 128: ffffff80 00 00 00 -128 0 0 0 255: ffffffff 00 00 00 -1 0 0 0 256: 00 01 00 00 0 1 0 0 I understand the values for 127 and 256, but why do the numbers change when going to 128? Why wouldn't it just be: 80 00 00 00 128 0 0 0 Am I forgetting to do something in the conversion process or am I forgetting something about integer representation? *Note: This is just a small test program. In a real program I have more in the struct, better variable names, and I convert to little-endian. *Edit: formatting

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• Deterministic and non uniform long string generation from seed

  - by Limonup

  I had this weird idea for an encryption that I wanted to try out, it may be bad, and it may have done before, but I'm just doing it for fun. The short version of the question is: Is it possible to generate a long, deterministic and non-uniformly distributed string/sequence of numbers from a small seed? Long(er) version: I was thinking to encrypt a text by changing encoding. The new encoding would be generated via Huffman algorithm. To work well, the Huffman algorithm would need a fairly long text with non uniform distribution. Then characters can have different bit-lengths which would be the primary strength of this encryption. The problem is that its impractical to enter in/remember a long text each time you want to decrypt the text. So I was wondering if it was possible to generate a text from password seed? It doesn't matter what the text is, as long as it has non uniform distribution of characters and that the exact same sequence can be recreated each time you give it the same seed. Preferably, are there any functions/extensions in Python that can do this? EDIT: To expand on the "strength" of varying bit length: if I have a string "test", ASCII values 116, 101, 115, 116, which gives bit values of 1110100 1100101 1110011 1110100 Then, say my Huffman algorithm generates encoding like t = 101 e = 1100111 s = 10001 The final string is 101 1100111 10001 101, if we encode this back to ASCII, we get 1011100 1111000 1101000, which is 3 entirely different characters. Obviously its impossible to perform any kind of frequency analysis or something like that on this.

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• How to pass a value from the Jquery validation

  - by user2963960

  How can i pass a value from the jquery validation. I have an input box named clubCardNumber it should validate the length of the inputted value. If the length is equal to 10 the value passes to the hidden field named else validated it if its null or empty if all validations are true then its a clubCard. Here is how i implemented it on Javascript function validateClubCardNumber() { var varClubCardNumber = $('#clubCardNumber').val(); $('#phoneNumber').val(""); var returnVal = true; if ((null == varClubCardNumber || '' == trim(varClubCardNumber)){ return false; } if( varClubCardNumber.length < 10 ){ return false; }else if( varClubCardNumber.length == 10 ) { //The Phone Number field should contains numbers only var pattern = /^[0-9 -]*$/ ; var flag = pattern.test(trim(varClubCardNumber)); if(flag == false){ return false; }else{ $('#phoneNumber').val(varClubCardNumber); returnVal = true; } } } return returnVal; } HTML <div > <label for="clubCardNumber" >Card or Phone Number:</label> <input id="clubCardNumber" name="clubCardNumber" type="text" placeholder="Card or Phone Number" value="" maxlength="20"/> </div> <input type="hidden" id="phoneNumber" name="phoneNumber" value=""/>

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• changing default my.cnf path in mysql

  - by user377941

  I am having two mysql instances on same machine. The installations are on /usr/loca/mysql1 and /usr/local/mysql2. I m having separate my.cnf files located in /etc/mysql1 and /etc/mysql2. I installed the first instance of my sql using source distribution and with the --prefix=/usr/local/mysql1 option. The second one i got from copying and pastinf the same directory to /usr/local/mysql2. When i start the mysql daemon on /usr.local/mysql/libexec it reads the my.cnf file in /etc/mysql1. And if i start the mysql daemon in /usr/local/mysql2 it reads the same my.cnf file. I have separate port numbers and .sock files defined in the .cnf file in those 2 locations. I can read the my.cnf file in the second location by using --defaults-file=/etc/mysql2/my.cnf option on mysqld startup. I dnt need to enter this each and every time i start the daemon. If i am going to have more instances how can i point the correct my.cnf file to read to each and every mysql daemon. What is the retionale behind mysqld links with the my.cnf file. how can i predefine the location of my.cnf file for each instance.

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