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• How can I avoid hard-coding YubiKey user identities into the PAM stack?

  - by CodeGnome

  The Yubico PAM Module seems to require changes to the PAM stack for each user that will be authenticated with a YubiKey. Specifically, it seems that each user's client identity must be added to the right PAM configuration file before the user can be authenticated. While it makes sense to add authorized keys to an authentication database such as /etc/yubikey_mappings or ~/.yubico/authorized_yubikeys, it seems like a bad practice to have to edit the PAM stack itself for each individual user. I would definitely like to avoid having to hard-code user identities into the PAM stack this way. So, is it possible to avoid hard-coding the id parameter to the pam_yubico.so module itself? If not, are there any other PAM modules that can leverage YubiKey authentication without hard-coding the stack?

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• How do I debug a difficult-to-reproduce crash with no useful call stack?

  - by David M

  I am encountering an odd crash in our software and I'm having a lot of trouble debugging it, and so I am seeking SO's advice on how to tackle it. The crash is an access violation reading a NULL pointer: First chance exception at $00CF0041. Exception class $C0000005 with message 'access violation at 0x00cf0041: read of address 0x00000000'. It only happens 'sometimes' - I haven't managed to figure out any rhyme or reason, yet, for when - and only in the main thread. When it occurs, the call stack contains one incorrect entry: For the main thread, which this is, it should show a large stack full of other items. At this point, all other threads are inactive (mostly sitting in WaitForSingleObject or a similar function.) I have only seen this crash occur in the main thread. It always has the same call stack of one entry, in the same method at the same address. This method may or may not be related - we do use the VCL in our application. My bet, though, is that something (possibly quite a while ago) is corrupting the stack, and the address where it's crashing is effectively random. Note it has been the same address across several builds, though - it's probably not truly random. Here is what I've tried: Trying to reproduce it reliably at a certain point. I have found nothing that reproduces it every time, and a couple of things that occasionally do, or do not, for no apparent reason. These are not 'narrow' enough actions to narrow it down to a particular section of code. It may be timing related, but at the point the IDE breaks in, other threads are usually doing nothing. I can't rule out a threading problem, but think it's unlikely. Building with extra debugging statements (extra debug info, extra asserts, etc.) After doing so, the crash never occurs. Building with Codeguard enabled. After doing so, the crash never occurs and Codeguard shows no errors. My questions: 1. How do I find what code caused the crash? How do I do the equivalent of walking back up the stack? 2. What general advice do you have for how to trace the cause of this crash? I am using Embarcadero RAD Studio 2010 (the project mostly contains C++ Builder code and small amounts of Delphi.)

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• How to impale and stack targets correctly according to the collider and its coordinate?

  - by David Dimalanta

  I'm making another simple game, a catch game, where a spawning target game object must be captured using a skewer to impale it. Here how: At the start, the falling object (in red) will fall in a vertical direction (in blue) When aimed properly, the target will fall down along the line of the skewer. (in blue) Then, another target is spawned and will fall vertically. (in red) When aimed successfully again in a streak, the second target will fall along the skewer and stacked. Same process over and over when another target is spawned. However, when I test run it on the scene tab in Unity, when impaled several targets, instead of a smooth flow and stacking it ended up overlaying it instead of stacking it up like a pancake. Here's what it look like: As I noticed when reaching the half-way of my progress, I tried to figure out how to deal with collider bodies without sticking each other so that it will actually stack like in the example of the image at no. 3. Here's the script code I added in the target game object: using UnityEngine; using System.Collections; public class ImpaleStateTest : MonoBehaviour { public GameObject target; public GameObject skewer; public bool drag = false; private float stack; private float impaleCount; void Start () { stack = 0; impaleCount = 0; } void Update () { if(drag) { target.transform.position = new Vector3 (DragTest.dir.transform.position.x, DragTest.dir.transform.position.y - 0.35f, 0); target.transform.rotation = DragTest.degrees; target.rigidbody2D.fixedAngle = true; target.rigidbody2D.isKinematic = true; target.rigidbody2D.gravityScale = 0; if(Input.GetMouseButton(0)) { Debug.Log ("Skewer: " + DragTest.dir.transform.position.x); Debug.Log ("Target: " + target.transform.position.x); } } } void OnTriggerEnter2D(Collider2D collider) { impaleCount++; Debug.Log ("Impaled " + impaleCount + " time(s)!"); drag = true; audio.Play (); } } Aside from that, I'm not sure if it's right but, the only way to stick the impaled targets while dragging the skewer left or right is to get the X coordinates from the skewer only. Is there something else to recommend it in order to improve this behavior as realistic as possible? Please help.

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• Android Loading Screen: How do I use a stack to load elements?

  - by tom_mai78101

  I have some problems with figuring out what value I should put in the function: int value_needed_to_figure_out = X; ProgressBar.incrementProgressBy(value_needed_to_figure_out); I've been researching about loading screens and how to use them. Some examples I've seen have implemented Thread.sleep() in a Handler.post(new Runnable()) function. To me, I got most of that concept of using the Handler to update the ProgressBar, while pretending to do some heavy crunching work. So, I kept looking. I have read this thread here: How do I load chunks of data from an assest manager during a loading screen? It said that I can try using a stack it needs to load, and adding a size counter as I add elements to the stack. What does it mean? This is the part where I'm totally stumped. If anyone would provide some hints, I'll gladly appreciate it. Thanks in advance.

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• 6 important .NET concepts: - Stack, heap, Value types, reference types, boxing and Unboxing.

  6 important .NET concepts: - Stack, heap, Value types, reference types, boxing and Unboxing.

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• Android Loading Screen: How do I go about using a stack to load elements, and the option of incrementing the size counter?

  - by tom_mai78101

  I have some problems with figuring out what value I should put in the function: int value_needed_to_figure_out = X; ProgressBar.incrementProgressBy(value_needed_to_figure_out); I've been researching about loading screens and how to use them. Some examples I've seen have implemented Thread.sleep() in a Handler.post(new Runnable()) function. To me, I got most of that concept of using the Handler to update the ProgressBar, while pretending to do some heavy crunching work. So, I kept looking. I have read this thread here: How do I load chunks of data from an assest manager during a loading screen? It said that I can try using a stack it needs to load, and adding a size counter as I add elements to the stack. What does it mean? This is the part where I'm totally stumped. If anyone would provide some hints, I'll gladly appreciate it. Thanks in advance.

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• Is it possible to create thread-safe collections without locks?

  - by Andrey

  This is pure just for interest question, any sort of questions are welcome. So is it possible to create thread-safe collections without any locks? By locks I mean any thread synchronization mechanisms, including Mutex, Semaphore, and even Interlocked, all of them. Is it possible at user level, without calling system functions? Ok, may be implementation is not effective, i am interested in theoretical possibility. If not what is the minimum means to do it? EDIT: Why immutable collections don't work. This of class Stack with methods Add that returns another Stack. Now here is program: Stack stack = new ...; ThreadedMethod() { loop { //Do the loop stack = stack.Add(element); } } this expression stack = stack.Add(element) is not atomic, and you can overwrite new stack from other thread. Thanks, Andrey

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• A error about "Address 0x0 is not stack'd, malloc'd or (recently) free'd" in c program under linux

  - by MaiTiano

  There is a piece of my program: height = atoi(argv[3]); width = atoi(argv[2]); sprintf(seqName,"%s", argv[1]); // strcpy(seqName, argv[1]); After compiling it, a exe file test is generated, then I use Valgrind to check it. Then I got the following message, however I cannot understand what it tends to tell me. Can anyone provide some kind help, Thanks. 1 contexts (suppressed: 13 from 8) 1 contexts (suppressed: 13 from 8) jl@ubuntu:~/work/dsr_analysis$ valgrind --tool=memcheck --leak-check=yes ./test ==28940== Memcheck, a memory error detector ==28940== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al. ==28940== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info ==28940== Command: ./test ==28940== ==28940== Invalid read of size 1 ==28940== at 0x40260CA: strcpy (mc_replace_strmem.c:311) ==28940== by 0x804A5C6: main (me_search.c:1428) ==28940== Address 0x0 is not stack'd, malloc'd or (recently) free'd ==28940== ==28940== ==28940== Process terminating with default action of signal 11 (SIGSEGV) ==28940== Access not within mapped region at address 0x0 ==28940== at 0x40260CA: strcpy (mc_replace_strmem.c:311) ==28940== by 0x804A5C6: main (me_search.c:1428) ==28940== If you believe this happened as a result of a stack ==28940== overflow in your program's main thread (unlikely but ==28940== possible), you can try to increase the size of the ==28940== main thread stack using the --main-stacksize= flag. ==28940== The main thread stack size used in this run was 8388608. ==28940== ==28940== HEAP SUMMARY: ==28940== in use at exit: 0 bytes in 0 blocks ==28940== total heap usage: 0 allocs, 0 frees, 0 bytes allocated ==28940== ==28940== All heap blocks were freed -- no leaks are possible ==28940== ==28940== For counts of detected and suppressed errors, rerun with: -v ==28940== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 13 from 8)1 contexts (suppressed: 13 from 8) 1 contexts (suppressed: 13 from 8)

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• C#/.NET library for source code formatting, like the one used by Stack Overflow?

  - by Lasse V. Karlsen

  I am writing a command line tool to convert Markdown text to html output, which seems easy enough. However, I am wondering how to get nice syntax coloring for embedded code blocks, like the one used by Stack Overflow. Does anyone know either: What library StackOverflow is using or if there's a library out there that I can easily reuse? Basically it would need to have some of the same "intelligence" found in the one that Stack Overflow uses, by basically doing a best-attempt at figuring out the language in use to pick the right keywords. Basically, what I want is for my own program to handle a block like the following: if (a == 0) return true; if (a == 1) return false; // fall-back Markdown Sharp, the library I'm using, by default outputs the above as a simple pre/code html block, with no syntax coloring. I'd like the same type of handling as the formatting on Stack Overflow does, the above contains blue "return" keywords for example. Or, hmm, after checking the source of this Stack Overflow page after adding the code example, I notice that it too is formatted like a simple pre/code block. Is it pure javascript-magic at works here, so perhaps there's no such library? If there's no library that will automagically determine a possible language by the keywords used, is there one that would work if I explicitly told it the language? Since this is "my" markdown-commandline-tool, I can easily add syntax if I need to.

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• Catching a nested-in-template exception [C++]

  - by Karol

  Hello, I have a problem with writing a catch clause for an exception that is a class nested in a template. To be more specific, I have a following definition of the template and exception: /** Generic stack implementation. Accepts std::list, std::deque and std::vector as inner container. */ template < typename T, template < typename Element, typename = std::allocator<Element> > class Container = std::deque > class stack { public: class StackEmptyException { }; ... /** Returns value from the top of the stack. Throws StackEmptyException when the stack is empty. */ T top() const; ... } I have a following template method that I want exception to catch: template <typename Stack> void testTopThrowsStackEmptyExceptionOnEmptyStack() { Stack stack; std::cout << "Testing top throws StackEmptyException on empty stack..."; try { stack.top(); } catch (Stack::StackEmptyException) { // as expected. } std::cout << "success." << std::endl; } When I compile it (-Wall, -pedantic) I get the following error: In function ‘void testTopThrowsStackEmptyExceptionOnEmptyStack()’: error: expected type-specifier error: expected unqualified-id before ‘)’ token === Build finished: 2 errors, 0 warnings === Thanks in advance for any help! What is interesting, if the stack implementation was not a template, then the compiler would accept the code as it is.

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• How to perform a Depth First Search iteratively using async/parallel processing?

  - by Prabhu

  Here is a method that does a DFS search and returns a list of all items given a top level item id. How could I modify this to take advantage of parallel processing? Currently, the call to get the sub items is made one by one for each item in the stack. It would be nice if I could get the sub items for multiple items in the stack at the same time, and populate my return list faster. How could I do this (either using async/await or TPL, or anything else) in a thread safe manner? private async Task<IList<Item>> GetItemsAsync(string topItemId) { var items = new List<Item>(); var topItem = await GetItemAsync(topItemId); Stack<Item> stack = new Stack<Item>(); stack.Push(topItem); while (stack.Count > 0) { var item = stack.Pop(); items.Add(item); var subItems = await GetSubItemsAsync(item.SubId); foreach (var subItem in subItems) { stack.Push(subItem); } } return items; } EDIT: I was thinking of something along these lines, but it's not coming together: var tasks = stack.Select(async item => { items.Add(item); var subItems = await GetSubItemsAsync(item.SubId); foreach (var subItem in subItems) { stack.Push(subItem); } }).ToList(); if (tasks.Any()) await Task.WhenAll(tasks); UPDATE: If I wanted to chunk the tasks, would something like this work? foreach (var batch in items.BatchesOf(100)) { var tasks = batch.Select(async item => { await DoSomething(item); }).ToList(); if (tasks.Any()) { await Task.WhenAll(tasks); } } The language I'm using is C#.

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• Unable to access stackexchange sites from this system

  - by Sandeepan Nath

  Earlier, I was not able to access most of the stackexchange sites like stackoverflow, programmers.SE etc. on my home Windows XP system. I was able to access only a few like http://meta.stackexchange.com and not even http://www.meta.stackexchange.com (note the www). I tried many other sites like http://www.stackoverflow.com, http://area51.stackexchange.com/ but was getting page not found errors on all browsers. Even pinging from terminal was saying destination host unreachable. I did not check recently but may be all SE sites are unreachable now. I was clueless about what could be the issue. I thought some firewall issue? So, I stopped AVG antivirus's firewall, then completely uninstalled it and even turned of windows firewall. But still not reachable even after fresh installation of Windows 7. Then I noticed a "Too many requests" notice on google. This page - http://www.google.co.in/sorry/?continue=http://www.google.co.in/# I don't know why this appeared but I guess somehow too many requests might have been sent to these sites and they blocked me. But in that case, SE would be smart enough to show a captcha like google. So, how to confirm the problem and fix it. Similar questions like these don't look solved yet - Unable to access certain websites Unable to Access Certain Websites I have lately started actively participating in lots of SE sites. There are new new questions popping up in my mind every time and I am not able to ask them. Please help! Thanks

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• Buyers question: Have intel AES-NI already been integrated in IPSEC stacks?

  - by deploymonkey

  Dear serverfault, I need to decide between deploying Opteron 6100 and Xeon Westmere EP, so I regard this a platform question. If not, it may be moved to stackoverflow and I hereby declare that I am very sorry. Do any (F)OSS or proprietory IPSEC stacks already use the AES-NI functions of the Westmere-EP? Thanks a bundle! ps. If anyone would like to create the tag AES-NI, You're welcome. I couldn't due to lack of rep.

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• cannot evaluate expression because a native frame is on top of the call stack and system.accessviolationexception

  - by Joseph

  I have this code using c#. public partial class MainForm : Form { private CvCapture VideoCapture; private IplImage frame; private IplImage imgMain; public MainForm() { InitializeComponent(); } private void btnVideo_Click(object sender, EventArgs e) { double vidWidth, vidHeight; try { VideoCapture = highgui.CvCreateCameraCapture(0); } catch (Exception except) { MessageBox.Show(except.Message); } if (btnVideo.Text.CompareTo("Start Video") == 0) { if (VideoCapture.ptr == IntPtr.Zero) { MessageBox.Show("badtrip ah!!!"); return; } btnVideo.Text = "Stop Video"; highgui.CvSetCaptureProperty(ref VideoCapture, highgui.CV_CAP_PROP_FRAME_WIDTH, 640); highgui.CvSetCaptureProperty(ref VideoCapture, highgui.CV_CAP_PROP_FRAME_HEIGHT, 480); highgui.CvQueryFrame(ref VideoCapture); vidWidth = highgui.cvGetCaptureProperty(VideoCapture, highgui.CV_CAP_PROP_FRAME_WIDTH); vidHeight = highgui.cvGetCaptureProperty(VideoCapture, highgui.CV_CAP_PROP_FRAME_HEIGHT); picBoxMain.Width = (int)vidWidth; picBoxMain.Height = (int)vidHeight; timerGrab.Enabled = true; timerGrab.Interval = 42; timerGrab.Start(); } else { btnVideo.Text = "Start Video"; timerGrab.Enabled = false; if (VideoCapture.ptr == IntPtr.Zero) { highgui.CvReleaseCapture(ref VideoCapture); VideoCapture.ptr = IntPtr.Zero; } } } private void timerGrab_Tick(object sender, EventArgs e) { try { frame = highgui.CvQueryFrame(ref VideoCapture); if (frame.ptr == IntPtr.Zero) { timerGrab.Stop(); MessageBox.Show("??"); return; } imgMain = cxcore.CvCreateImage(cxcore.CvGetSize(ref frame), 8, 3); picBoxMain.Image = highgui.ToBitmap(imgMain, false); cxcore.CvReleaseImage(ref imgMain); //cxcore.CvReleaseImage(ref frame); } catch (Exception excpt) { MessageBox.Show(excpt.Message); } } } The problem is after i break all and step through the debugger the program stops at a certain code. the code where it stops is here: frame = highgui.CvQueryFrame(ref VideoCapture); the error is that it says that cannot evaluate expression because a native frame is on top of the call stack. and then when i try to shift+F11 it. there is another error saying that system.accessviolationexception. the stack trace says that: at System.Runtime.InteropServices.Marshal.CopyToManaged(IntPtr source, Object destination, Int32 startIndex, Int32 length) at CxCore.IplImage.get_ImageDataDb()

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• Obtaining references to function objects on the execution stack from the frame object?

  - by Marcin

  Given the output of inspect.stack(), is it possible to get the function objects from anywhere from the stack frame and call these? If so, how? (I already know how to get the names of the functions.) Here is what I'm getting at: Let's say I'm a function and I'm trying to determine if my caller is a generator or a regular function? I need to call inspect.isgeneratorfunction() on the function object. And how do you figure out who called you? inspect.stack(), right? So if I can somehow put those together, I'll have the answer to my question. Perhaps there is an easier way to do this?

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• How are exceptions allocated on the stack caught beyond their scope?

  - by John Doe

  In the following code, the stack-based variable 'ex' is thrown and caught in a function beyond the scope in which ex was declared. This seems a bit strange to me, since (AFAIK) stack-based variables cannot be used outside the scope in which they were declared (the stack is unwound). void f() { SomeKindOfException ex(...); throw ex; } void g() { try { f(); } catch (SomeKindOfException& ex) { //Handling code... } } I've added a print statement to SomeKindOfException's destructor and it shows that ex is destructed once it goes out of scope in f() but then it's caught in g() and destructed again once it goes out of scope there as well. Any help?

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• how do I filter RoutingErrors and their long stack trace out of my log? rails

  - by codeman73

  I am seeing several strange requests like this, with urls like /sitemap/, /google_sitemap.xml.gz, /sitemap.xml.gz, /google_sitemap.xml, /cgi-bin/awstat/awstats.pl, etc. The default rails behavior dumps these long stack traces into my log, like the following: ActionController::RoutingError (No route matches "/rails/info/properties" with {:method=>:get}): /dh/passenger/lib/phusion_passenger/rack/request_handler.rb:92:in `process_request' /dh/passenger/lib/phusion_passenger/abstract_request_handler.rb:207:in `main_loop' /dh/passenger/lib/phusion_passenger/railz/application_spawner.rb:400:in `start_request_handler' /dh/passenger/lib/phusion_passenger/railz/application_spawner.rb:351:in `handle_spawn_application' /dh/passenger/lib/phusion_passenger/utils.rb:184:in `safe_fork' etc. Is there any way to stop these long stack traces? I wouldn't mind the first line, the ActionController::RoutingError with the message and the url, but I'd like to get rid of the long stack of passenger stuff.

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• Why does s ++ t not lead to a stack overflow for large s?

  - by martingw

  I'm wondering why Prelude> head $ reverse $ [1..10000000] ++ [99] 99 does not lead to a stack overflow error. The ++ in the prelude seems straight forward and non-tail-recursive: (++) :: [a] -> [a] -> [a] (++) [] ys = ys (++) (x:xs) ys = x : xs ++ ys So just with this, it should run into a stack overflow, right? So I figure it probably has something to do with the ghc magic that follows the definition of ++: {-# RULES "++" [~1] forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys #-} Is that what helps avoiding the stack overflow? Could someone provide some hint for what's going on in this piece of code?

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• What is on the 68000 stack when classic MacOS enters a program?

  - by John Källén

  I'm trying to understand an old classic Mac application's entry point. I've disassembled the first CODE resource (not CODE#0, which is the jump table). The code refers to some variables off the stack: a word at 0004(A7), an array of long words of starting at 000C(A7) whose length is the value at 0004(A7), and a final long word beyond that array that seems to be a pointer to a character string. The array of long words looks like strings at first glance, so it looks superficially like we're dealing with an (int argc, char ** argv) situation, except the "argv" array is inline in the stack frame. What should a program be expecting on its stack / registers when it first gets called by the Mac OS?

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• Would someone mind giving suggestions for this new assembly language?

  - by Noctis Skytower

  Greetings! Last semester in college, my teacher in the Computer Languages class taught us the esoteric language named Whitespace. In the interest of learning the language better with a very busy schedule (midterms), I wrote an interpreter and assembler in Python. An assembly language was designed to facilitate writing programs easily, and a sample program was written with the given assembly mnemonics. Now that it is summer, a new project has begun with the objective being to rewrite the interpreter and assembler for Whitespace 0.3, with further developments coming afterwards. Since there is so much extra time than before to work on its design, you are presented here with an outline that provides a revised set of mnemonics for the assembly language. This post is marked as a wiki for their discussion. Have you ever had any experience with assembly languages in the past? Were there some instructions that you thought should have been renamed to something different? Did you find yourself thinking outside the box and with a different paradigm than in which the mnemonics were named? If you can answer yes to any of those questions, you are most welcome here. Subjective answers are appreciated! hold N Push the number onto the stack copy Duplicate the top item on the stack copy N Copy the nth item on the stack (given by the argument) onto the top of the stack swap Swap the top two items on the stack drop Discard the top item on the stack drop N Slide n items off the stack, keeping the top item add Addition sub Subtraction mul Multiplication div Integer Division mod Modulo save Store load Retrieve L: Mark a location in the program call L Call a subroutine goto L Jump unconditionally to a label if=0 L Jump to a label if the top of the stack is zero if<0 L Jump to a label if the top of the stack is negative return End a subroutine and transfer control back to the caller exit End the program print chr Output the character at the top of the stack print int Output the number at the top of the stack input chr Read a character and place it in the location given by the top of the stack input int Read a number and place it in the location given by the top of the stack Question: How would you redesign, rewrite, or rename the previous mnemonics and for what reasons?

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• My first Windows Phone 7 application is live &ndash; from zero to submitted in 5 hours

  - by Eric Nelson

  Tuesday evening I found myself minus family. I decided to use the time to “have a crack at this Silverlight Phone 7 stuff”. From zero (no experience, no tools installed, no membership on the AppHub) to submitted for approval took me from 8pm to 1am – with the last hour messing around with png files in Paint to complete the submission process! Two days later on Thursday it was approved and is now in the marketplace for you to install - or not :-) The application is very simple but it works and looks “finished” – and importantly I learnt a lot about what is involved and the power of our tooling to make this pretty easy to get going. Go on, give it a go by popping over to the App Hub. You do need to pay $99 to join the App Hub to publish but you can start by downloading the free tools and just work with the included emulator. Related Links https://create.msdn.com/ App Hub http://msdn.microsoft.com/library/ff402535.aspx MSDN Documentation for Phone 7 Development

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• Faille zero-day découverte dans Internet Explorer, permettant de prendre à distance le contrôle d'un PC, Microsoft recommande EMET

  Faille zero-day découverte dans Internet Explorer permettant de prendre à distance le contrôle d'un ordinateur, Microsoft recommande EMET Une faille de sécurité critique dans Internet Explorer 6, 7, 8 et 9 vient d'être découverte par des experts en sécurité. Dans un billet de blog sur ZATAZ.com, Eric Romang, un conseiller en sécurité luxembourgeois, déclare avoir découvert la vulnérabilité lorsque son PC a été infecté par le cheval de troie Poison Ivy, qui est utilisé pour voler des données ou prendre le contrôle à distance d'un ordinateur. La faille pourrait être exploitée par des pirates distants qui peuvent obtenir les mêmes privilèges que l'utilisateur local, pour installer de...

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• Finding N contiguous zero bits in an integer to the left of the MSB position of another integer

  - by James Morris

  The problem is: given an integer val1 find the position of the highest bit set (Most Significant Bit) then, given a second integer val2 find a contiguous region of unset bits, with the minimum number of zero bits given by width to the left of the position (ie, in the higher bits). Here is the C code for my solution: typedef unsigned int t; unsigned const t_bits = sizeof(t) * CHAR_BIT; _Bool test_fit_within_left_of_msb( unsigned width, t val1, t val2, unsigned* offset_result) { unsigned offbit = 0; unsigned msb = 0; t mask; t b; while(val1 >>= 1) ++msb; while(offbit + width < t_bits - msb) { mask = (((t)1 << width) - 1) << (t_bits - width - offbit); b = val2 & mask; if (!b) { *offset_result = offbit; return true; } if (offbit++) /* this conditional bothers me! */ b <<= offbit - 1; while(b <<= 1) offbit++; } return false; } Aside from faster ways of finding the MSB of the first integer, the commented test for a zero offbit seems a bit extraneous, but necessary to skip the highest bit of type t if it is set. I have also implemented similar algorithms but working to the right of the MSB of the first number, so they don't require this seemingly extra condition. How can I get rid of this extra condition, or even, are there far more optimal solutions? Edit: Some background not strictly required. The offset result is a count of bits from the high bit, not from the low bit as maybe expected. This will be part of a wider algorithm which scans a 2D array for a 2D area of zero bits. Here, for testing, the algorithm has been simplified. val1 represents the first integer which does not have all bits set found in a row of the 2D array. From this the 2D version would scan down which is what val2 represents. Here's some output showing success and failure: t_bits:32 t_high: 10000000000000000000000000000000 ( 2147483648 ) --------- ----------------------------------- *** fit within left of msb test *** ----------------------------------- val1: 00000000000000000000000010000000 ( 128 ) val2: 01000001000100000000100100001001 ( 1091569929 ) msb: 7 offbit:0 + width: 8 = 8 mask: 11111111000000000000000000000000 ( 4278190080 ) b: 01000001000000000000000000000000 ( 1090519040 ) offbit:8 + width: 8 = 16 mask: 00000000111111110000000000000000 ( 16711680 ) b: 00000000000100000000000000000000 ( 1048576 ) offbit:12 + width: 8 = 20 mask: 00000000000011111111000000000000 ( 1044480 ) b: 00000000000000000000000000000000 ( 0 ) offbit:12 iters:10 ***** found room for width:8 at offset: 12 ***** ----------------------------------- *** fit within left of msb test *** ----------------------------------- val1: 00000000000000000000000001000000 ( 64 ) val2: 00010000000000001000010001000001 ( 268469313 ) msb: 6 offbit:0 + width: 13 = 13 mask: 11111111111110000000000000000000 ( 4294443008 ) b: 00010000000000000000000000000000 ( 268435456 ) offbit:4 + width: 13 = 17 mask: 00001111111111111000000000000000 ( 268402688 ) b: 00000000000000001000000000000000 ( 32768 ) ***** mask: 00001111111111111000000000000000 ( 268402688 ) offbit:17 iters:15 ***** no room found for width:13 ***** (iters is the count of iterations of the inner while loop)

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• Why can't I store a float value - it's always zero!

  - by just_another_coder

  I have a view controller that is created by the app delegate - it's the first one shown in the app. In its interface I declare float lengthOfTime; I also set it as a property: @property (nonatomic) float lengthOfTime; And in it's implemetation: @synthesize lengthOfTime; In the class viewDidLoad method, I set the value: self.lengthOfTime = 3.0f; However, after this, the value is always zero. No errors, no compile warnings, nothing. Just zero. The class is instantiated, it is showing in the view, so I'm pretty sure it's not a nil reference. I've searched all over Google and can't figure it out. What's going on?!? :(

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• Is there a need for zero-out DIV's margin and padding?

  - by ssg

  I wonder if on any browser div element comes with a preset margin/padding value other than zero. As far as I know, div and span come with zero padding and margin values by standard to make them suitable canvas for style decoration. Even better, is there a definite standard for default styles for all elements that is cross-browser which we can make assumptions upon? For instance FORM comes with top/bottom margins, OL/UL come with padding-left's. I occasionally see a * { margin: 0; padding: 0; } and this just looks like a dirty hack without knowing the reasons or consequences. Anyone has any better approach to this?

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