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  • Hidden features of Perl?

    - by Adam Bellaire
    What are some really useful but esoteric language features in Perl that you've actually been able to employ to do useful work? Guidelines: Try to limit answers to the Perl core and not CPAN Please give an example and a short description Hidden Features also found in other languages' Hidden Features: (These are all from Corion's answer) C# Duff's Device Portability and Standardness Quotes for whitespace delimited lists and strings Aliasable namespaces Java Static Initalizers JavaScript Functions are First Class citizens Block scope and closure Calling methods and accessors indirectly through a variable Ruby Defining methods through code PHP Pervasive online documentation Magic methods Symbolic references Python One line value swapping Ability to replace even core functions with your own functionality Other Hidden Features: Operators: The bool quasi-operator The flip-flop operator Also used for list construction The ++ and unary - operators work on strings The repetition operator The spaceship operator The || operator (and // operator) to select from a set of choices The diamond operator Special cases of the m// operator The tilde-tilde "operator" Quoting constructs: The qw operator Letters can be used as quote delimiters in q{}-like constructs Quoting mechanisms Syntax and Names: There can be a space after a sigil You can give subs numeric names with symbolic references Legal trailing commas Grouped Integer Literals hash slices Populating keys of a hash from an array Modules, Pragmas, and command-line options: use strict and use warnings Taint checking Esoteric use of -n and -p CPAN overload::constant IO::Handle module Safe compartments Attributes Variables: Autovivification The $[ variable tie Dynamic Scoping Variable swapping with a single statement Loops and flow control: Magic goto for on a single variable continue clause Desperation mode Regular expressions: The \G anchor (?{}) and '(??{})` in regexes Other features: The debugger Special code blocks such as BEGIN, CHECK, and END The DATA block New Block Operations Source Filters Signal Hooks map (twice) Wrapping built-in functions The eof function The dbmopen function Turning warnings into errors Other tricks, and meta-answers: cat files, decompressing gzips if needed Perl Tips See Also: Hidden features of C Hidden features of C# Hidden features of C++ Hidden features of Java Hidden features of JavaScript Hidden features of Ruby Hidden features of PHP Hidden features of Python

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  • Hex representation of Euro Symbol €

    - by Rahul
    Hi I was using XVI32 (Hex Editor) to get the hex representation of the Euro symbol and it gives me the value as 80. Another site: http://www.string-functions.com/string-hex.aspx does the same. I am not able to understand why the hex representation is 80 instead of 0x20AC. This 0X80 gives 128 in decimal and if I use Alt+0128 it actually produces the Euro symbol. Could somebody throw some light on what could be the logic behind this conversion from string to hex conversion ? Thanks

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  • Extracting images from a PDF

    - by sagar
    My Query I want to extract only images from a PDF document, using Objective-C in an iPhone Application. My Efforts I have gone through the info on this link, which has details regarding different operators on PDF documents. I also studied this document from Apple about PDF parsing with Quartz. I also went through the entire PDF reference document from the Adobe site. According to that document, for each image there are the following operators: q Q BI EI I have created a table to get the image: myTable = CGPDFOperatorTableCreate(); CGPDFOperatorTableSetCallback(myTable, "q", arrayCallback2); CGPDFOperatorTableSetCallback(myTable, "TJ", arrayCallback); CGPDFOperatorTableSetCallback(myTable, "Tj", stringCallback); I use this method to get the image: void arrayCallback2(CGPDFScannerRef inScanner, void *userInfo) { // THIS DOESN'T WORK // CGPDFStreamRef stream; // represents a sequence of bytes // if (CGPDFDictionaryGetStream (d, "BI", &stream)){ // CGPDFDataFormat t=CGPDFDataFormatJPEG2000; // CFDataRef data = CGPDFStreamCopyData (stream, &t); // } } This method is called for the operator "q", but I don't know how to extract an image from it. What should be the solution for extracting the images from the PDF documents? Thanks in advance for your kind help.

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  • cygwin slow file open

    - by Erdem
    My application uses fopen to open a lot of files. While in linux opening and reading thousand of files doesn't even take a second; in cygwin it takes more than 5 seconds. I think it is because path conversion functions in cygwin dlls. 'open' function is a bit faster. If I use -mno-cygwin it becomes very fast but I can't use it. Is there an easy way to make cygwin dlls just open files; without any linux-windows conversion?

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  • .NET equivalent to Perl regular expressions

    - by r_honey
    I need to convert a Perl script to VB.NET. I have managed almost the entire conversion, but some Perl (seemingly simple) regex are causing an headache. Can someone suggest me .NET equivalent of the following perl regex: 1) $letter =~ s/Users //,; $letter =~ s/Mailboxes //,; if($letter =~ m/$first_char/i){ 2) unless($storegroup =~ /Recovery/ || $storegroup =~ /Users U V W X Y Z/ || $storegroup =~ /Users S T/ || $storegroup =~ /Users Q R/){ The regex look simple to me. I tried to wade through perl.org but understanding a langugae regex takes sometime and I need to complete the conversion quickly.

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  • Regex problem in Java in code sample

    - by JaneNY
    I have job with regex in my expressions: example !(FA1_A.i & FA1_M.i) I have operators ! ( ) & | operands have names [a-zA-Z_]*.[a-zA-Z_] I wrote in Java to split on tokens, but it doesn't split on operators and operands If should be !, (, FA1_A.i, &, FA1_m.i, ) . Can anybody tell me what is wrong ? String stringOpеrator = "([!|&()])"; String stringOperand = "(([a-zA-Z_]*)\\.([a-zA-Z_]*))"; String reg=stringOpеrator+"|"+stringOperand; Pattern pattern = Pattern.compile(reg); Matcher m = pattern.matcher(expression); // System.out.println("func: " + function + " item: " + item); while (m.find()) { int a=m.start(); int b=m.end(); String test=expression.substring(m.start(), m.end()); String g=test; tokens.add(new Token(expression.substring(m.start() , m.end()))); //m = pattern.matcher(expression); }

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  • Where are the real risks in network security?

    - by Barry Brown
    Anytime a username/password authentication is used, the common wisdom is to protect the transport of that data using encryption (SSL, HTTPS, etc). But that leaves the end points potentially vulnerable. Realistically, which is at greater risk of intrusion? Transport layer: Compromised via wireless packet sniffing, malicious wiretapping, etc. Transport devices: Risks include ISPs and Internet backbone operators sniffing data. End-user device: Vulnerable to spyware, key loggers, shoulder surfing, and so forth. Remote server: Many uncontrollable vulnerabilities including malicious operators, break-ins resulting in stolen data, physically heisting servers, backups kept in insecure places, and much more. My gut reaction is that although the transport layer is relatively easy to protect via SSL, the risks in the other areas are much, much greater, especially at the end points. For example, at home my computer connects directly to my router; from there it goes straight to my ISPs routers and onto the Internet. I would estimate the risks at the transport level (both software and hardware) at low to non-existant. But what security does the server I'm connected to have? Have they been hacked into? Is the operator collecting usernames and passwords, knowing that most people use the same information at other websites? Likewise, has my computer been compromised by malware? Those seem like much greater risks. What do you think?

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  • Can I compare a template variable to an integer in App Engine templates?

    - by matt b
    Using Django templates in Google App Engine (on Python), is it possible to compare a template variable to an integer in an {% if %} block? views.py: class MyHandler(webapp.RequestHandler): def get(self): foo_list = db.GqlQuery(...) ... template_values['foos'] = foo_list template_values['foo_count'] = len(foo_list) handler.response.out.write(template.render(...)) My template: {% if foo_count == 1 %} There is one foo. {% endif %} This blows up with 'if' statement improperly formatted. What I was attempting to do in my template was build a simple if/elif/else tree to be grammatically correct to be able to state #foo_count == 0: There are no foos. #foo_count == 1: There is one foo. #else: There are {{ foos|length }} foos. Browsing the Django template documents (this link provided in the GAE documentation appears to be for versions of Django far newer than what is supported on GAE), it appears as if I can only actually use boolean operators (if in fact boolean operators are supported in this older version of Django) with strings or other template variables. Is it not possible to compare variables to integers or non-strings with Django templates? I'm sure there is an easy way to workaround this - built up the message string on the Python side rather than within the template - but this seems like such a simple operation you ought to be able to handle in a template. It sounds like I should be switching to a more advanced templating engine, but as I am new to Django (templates or any part of it), I'd just like some confirmation first.

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  • Weird generics compile error.

    - by Jouke van der Maas
    I have two classes, a base class and a child class. In the base class i define a generic virtual method: protected virtual Bar Foo<T() where T : Bar {} Then in my child class i try to do this: protected override BarChild Foo() // BarChild inherits Bar { return base.Bar<T as BarChild() } Visual studio gives this weird error: The type 'T' cannot be used as type parameter 'T' in the generic type or method 'Foo()'. There is no boxing conversion or type parameter conversion from 'T' to 'Bar'. Repeating the where clause on the child's override also gives an error: Constraints for override and explicit interface implementation methods are inherited from the base method, so they cannot be specified directly So what am i doing wrong here?

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  • How to format a function pointer?

    - by Longpoke
    Is there any way to print a pointer to a function in ANSI C? Of course this means you have to cast the function pointer to void pointer, but it appears that's not possible?? #include <stdio.h> int main() { int (*funcptr)() = main; printf("%p\n", (void* )funcptr); printf("%p\n", (void* )main); return 0; } $ gcc -ansi -pedantic -Wall test.c -o test test.c: In function 'main': test.c:6: warning: ISO C forbids conversion of function pointer to object pointer type test.c:7: warning: ISO C forbids conversion of function pointer to object pointer type $ ./test 0x400518 0x400518 It's "working", but non-standard...

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  • Precompile Lambda Expression Tree conversions as constants?

    - by Nathan
    It is fairly common to take an Expression tree, and convert it to some other form, such as a string representation (for example this question and this question, and I suspect Linq2Sql does something similar). In many cases, perhaps even most cases, the Expression tree conversion will always be the same, i.e. if I have a function public string GenerateSomeSql(Expression<Func<TResult, TProperty>> expression) then any call with the same argument will always return the same result for example: GenerateSomeSql(x => x.Age) //suppose this will always return "select Age from Person" GenerateSomeSql(x => x.Ssn) //suppose this will always return "select Ssn from Person" So, in essence, the function call with a particular argument is really just a constant, except time is wasted at runtime re-computing it continuously. Assuming, for the sake of argument, that the conversion was sufficiently complex to cause a noticeable performance hit, is there any way to pre-compile the function call into an actual constant?

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  • improving conversions to binary and back in C#

    - by Saad Imran.
    I'm trying to write a general purpose socket server for a game I'm working on. I know I could very well use already built servers like SmartFox and Photon, but I wan't to go through the pain of creating one myself for learning purposes. I've come up with a BSON inspired protocol to convert the the basic data types, their arrays, and a special GSObject to binary and arrange them in a way so that it can be put back together into object form on the client end. At the core, the conversion methods utilize the .Net BitConverter class to convert the basic data types to binary. Anyways, the problem is performance, if I loop 50,000 times and convert my GSObject to binary each time it takes about 5500ms (the resulting byte[] is just 192 bytes per conversion). I think think this would be way too slow for an MMO that sends 5-10 position updates per second with a 1000 concurrent users. Yes, I know it's unlikely that a game will have a 1000 users on at the same time, but like I said earlier this is supposed to be a learning process for me, I want to go out of my way and build something that scales well and can handle at least a few thousand users. So yea, if anyone's aware of other conversion techniques or sees where I'm loosing performance I would appreciate the help. GSBitConverter.cs This is the main conversion class, it adds extension methods to main datatypes to convert to the binary format. It uses the BitConverter class to convert the base types. I've shown only the code to convert integer and integer arrays, but the rest of the method are pretty much replicas of those two, they just overload the type. public static class GSBitConverter { public static byte[] ToGSBinary(this short value) { return BitConverter.GetBytes(value); } public static byte[] ToGSBinary(this IEnumerable<short> value) { List<byte> bytes = new List<byte>(); short length = (short)value.Count(); bytes.AddRange(length.ToGSBinary()); for (int i = 0; i < length; i++) bytes.AddRange(value.ElementAt(i).ToGSBinary()); return bytes.ToArray(); } public static byte[] ToGSBinary(this bool value); public static byte[] ToGSBinary(this IEnumerable<bool> value); public static byte[] ToGSBinary(this IEnumerable<byte> value); public static byte[] ToGSBinary(this int value); public static byte[] ToGSBinary(this IEnumerable<int> value); public static byte[] ToGSBinary(this long value); public static byte[] ToGSBinary(this IEnumerable<long> value); public static byte[] ToGSBinary(this float value); public static byte[] ToGSBinary(this IEnumerable<float> value); public static byte[] ToGSBinary(this double value); public static byte[] ToGSBinary(this IEnumerable<double> value); public static byte[] ToGSBinary(this string value); public static byte[] ToGSBinary(this IEnumerable<string> value); public static string GetHexDump(this IEnumerable<byte> value); } Program.cs Here's the the object that I'm converting to binary in a loop. class Program { static void Main(string[] args) { GSObject obj = new GSObject(); obj.AttachShort("smallInt", 15); obj.AttachInt("medInt", 120700); obj.AttachLong("bigInt", 10900800700); obj.AttachDouble("doubleVal", Math.PI); obj.AttachStringArray("muppetNames", new string[] { "Kermit", "Fozzy", "Piggy", "Animal", "Gonzo" }); GSObject apple = new GSObject(); apple.AttachString("name", "Apple"); apple.AttachString("color", "red"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)1.5); GSObject lemon = new GSObject(); apple.AttachString("name", "Lemon"); apple.AttachString("color", "yellow"); apple.AttachBool("inStock", false); apple.AttachFloat("price", (float)0.8); GSObject apricoat = new GSObject(); apple.AttachString("name", "Apricoat"); apple.AttachString("color", "orange"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)1.9); GSObject kiwi = new GSObject(); apple.AttachString("name", "Kiwi"); apple.AttachString("color", "green"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)2.3); GSArray fruits = new GSArray(); fruits.AddGSObject(apple); fruits.AddGSObject(lemon); fruits.AddGSObject(apricoat); fruits.AddGSObject(kiwi); obj.AttachGSArray("fruits", fruits); Stopwatch w1 = Stopwatch.StartNew(); for (int i = 0; i < 50000; i++) { byte[] b = obj.ToGSBinary(); } w1.Stop(); Console.WriteLine(BitConverter.IsLittleEndian ? "Little Endian" : "Big Endian"); Console.WriteLine(w1.ElapsedMilliseconds + "ms"); } Here's the code for some of my other classes that are used in the code above. Most of it is repetitive. GSObject GSArray GSWrappedObject

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  • What's the false operator in C# good for?

    - by Jakub Šturc
    There are two weird operators in C#: the true operator the false operator If I understand this right these operators can be used in types which I want to use instead of a boolean expression and where I don't want to provide an implicit conversion to bool. Let's say I have a following class: public class MyType { public readonly int Value; public MyType(int value) { Value = value; } public static bool operator true (MyType mt) { return mt.Value > 0; } public static bool operator false (MyType mt) { return mt.Value < 0; } } So I can write the following code: MyType mTrue = new MyType(100); MyType mFalse = new MyType(-100); MyType mDontKnow = new MyType(0); if (mTrue) { // Do something. } while (mFalse) { // Do something else. } do { // Another code comes here. } while (mDontKnow) However for all the examples above only the true operator is executed. So what's the false operator in C# good for? Note: More examples can be found here, here and here.

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  • Adobe Livecycle performance

    - by Fabio
    I have installed Adobe Livecycle in order to convert MSWORD files to PDF from a web-app. Specifically, I use the DocConverter tool. Previously I have used OpenOffice UNO SDK, but I have found some problems with particular documents. Now, the conversion is ok, but the conversion time is huge. These are the times to convert documents of different sizes via Openoffice and via Livecycle. Could you suggest anything? SIZE (bytes) Openoffice (sec) Adobe LiveCycle (sec) 24064 1 8 50688 0 3 100864 0 3 253952 0 5 509440 1 5 1017856 5 18 2098688 8 10 4042240 19 45 6281216 0 9 8212480 32 125

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  • Most Lite-Weight XML Parser with XPath and Wide-char Support

    - by Mystagogue
    I want a lite-weight C++ XML parser/DOM that: Can take UTF-8 as input, and parse into UTF-16. Maybe it does this directly (ideal!), or perhaps it provides a hook for the conversion (such as taking a custom stream object that does the conversion before parsing). Offers some XPath support. I've been looking at RapidXML, the Kranf xmlParser, and pugiXML. The first two of those might permit requirement #1 by way of a hook. The third, pugiXML, supports the #2 requirement. But none of those three fulfill both requirements. What is the smallest (free) library that can handle both requirements?

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  • TypeConverter.ConvertFrom String to String

    - by Ken
    I'm using a PropertyGrid to display a property. For one property, I'm displaying strings in a drop-down combobox. The displayed text of the property and the value of the property are both strings, but their text is different. The displayed text is friendly, the value text corresponds to a registry key name. I've created a TypeConverter to convert between the display text and the value text, but the ConvertFrom() method appears to work correctly until I change the combo-box selection. It then sends the 'value' text instead of the display text to use during the conversion. Has anyone else used string-to-string conversion successfully?

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  • How can I programatically convert SQL data-types to .Net data-types?

    - by Simon
    Can anyone show me a way of converting SQL Server data-types (varchar for example) to .Net data-types (String for example). I'm assuming that automatic conversion is not possible? I have an 'EntityProperty' object and would like it to have an appropriate 'Type' property (string, decimal, int32 etc), at the moment this property is just a string - 'int32' for example. A little background: I'm using SQL DMO in an internal code generation app to query a database and generate a stored procedure based DAL from the database. Being an internal app I can take quite a few shortcuts and make quite a few assumptions. To get the app working at the moment this data-type conversion is handled by a Select Case statement which just converts the types to strings and generates a set of properties based on these strings but I would prefer a little more flexibility in being able to handle the types (use of TypeOf etc). Anyone worked on something similar? I know EF, nHibernate, Subsonic etc could do all this for me but in this case, for various reasons, I am having to roll my own. :)

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  • Problem evaluating NULL in an IIF statement (Access)

    - by Mohgeroth
    Item in the recordset rstImportData("Flat Size") is = Null With that, given the following statement: IIF(IsNull(rstImportData("Flat Size")), Null, cstr(rstImportData("Flat Size"))) Result: Throws error 94: Invalid use of Null If I change the statement by removing the type conversion upon a false comparison: IIF(IsNull(rstImportData("Flat Size")), Null, 0) Result: Null It returns Null as it should have the first time. It appears that I cannot do a type conversion in an IIF if the value passed in should ever be null even if it passes an IIF test, it still attempts to evaluate it at both the true and false answer. The only reason I'm using IIF like this is because I have a 25 line comparison to compare data from an Import against a matching record in a database to see if I need to append the prior to history. Any thoughts? The way data is imported there will be null dates and where the spreadsheet import is in a string format I must convert either side to the other to compare the values properly but if either side is null this exception occurs :(

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  • Can I compare a template variable to an integer in Django/App Engine templates?

    - by matt b
    Using Django templates in Google App Engine (on Python), is it possible to compare a template variable to an integer in an {% if %} block? views.py: class MyHandler(webapp.RequestHandler): def get(self): foo_list = db.GqlQuery(...) ... template_values['foos'] = foo_list template_values['foo_count'] = len(foo_list) handler.response.out.write(template.render(...)) My template: {% if foo_count == 1 %} There is one foo. {% endif %} This blows up with 'if' statement improperly formatted. What I was attempting to do in my template was build a simple if/elif/else tree to be grammatically correct to be able to state #foo_count == 0: There are no foos. #foo_count == 1: There is one foo. #else: There are {{ foos|length }} foos. Browsing the Django template documents (this link provided in the GAE documentation appears to be for versions of Django far newer than what is supported on GAE), it appears as if I can only actually use boolean operators (if in fact boolean operators are supported in this older version of Django) with strings or other template variables. Is it not possible to compare variables to integers or non-strings with Django templates? I'm sure there is an easy way to workaround this - built up the message string on the Python side rather than within the template - but this seems like such a simple operation you ought to be able to handle in a template. It sounds like I should be switching to a more advanced templating engine, but as I am new to Django (templates or any part of it), I'd just like some confirmation first.

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  • Upgrading Visual Studio web service project says to "convert to web application."

    - by Buggieboy
    I have a Visual Studio 2003 web service project that I have to upgrade to Visual Studio 2008. After I have run the conversion wizard, I get this message: You have completed the first step in converting your Visual Studio .NET 2003 web project. To complete the conversion, please select your project in the Solution Explorer and choose the 'Convert to Web Application' context menu item. I got this message with another project, which was originally a "web site", rather than an ASP.NET "web application". It made sense to in that case (sort of). Why, however, would I not just want to have this project remain a web service project? Additionally, when I follow the instructions and select "Convert to Web Application" from the context menu, I don't get any feedback that anything has changed. Should it have? If so, what?

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  • parsing ip address in php

    - by Ryan
    Hi all, I am trying to create a page that shows the user their zip code when they are on my page. (if any of you are familiar with GeoIP data, thats what I am using. ) I have a conversion that converts the users IP address into an IP number, that conversion is: ipnum = 16777216*w + 65536*x + 256*y + z where w.x.y.z are the ip sections (000.000.000.000) My question is, using $_SERVER['REMOTE_ADDR']; is there a way for me to section the users ip address and assign the section of the ip address to variables? for example: usersip = 192.168.123.5 w = 192; x = 168; y = 123; z = 5; Thanks!

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  • Ruby: wait for system command to end

    - by Ignace
    Hey all, I'm converting an xls 2 csv with a system(command) in ruby. After the conversion i'm processing this csv files. But the conversion is still going when the program wants to process the files. So at that time they are non existant. Can someone tell me if it's possible to let Ruby wait the right amount of time for the system command to finish? Right now i'm using sleep 20 but if it will take longer once, it isn't right of course... Thanks!

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  • implementing cryptographic algorithms, specifically the key expansion part

    - by masseyc
    Hey, recently I picked up a copy of Applied Cryptography by Bruce Schneier and it's been a good read. I now understand how several algorithms outlined in the book work, and I'd like to start implementing a few of them in C. One thing that many of the algorithms have in common is dividing an x-bit key, into several smaller y-bit keys. For example, blowfish's key, X, is 64-bits, but you are required to break it up into two 32-bit halves; Xl and Xr. This is where I'm getting stuck. I'm fairly decent with C, but I'm not the strongest when it comes to bitwise operators and the like. After some help on IRC, I managed to come up with these two macros: #define splitup(a, b, c) {b = a >> 32; c = a & 0xffffffff; } #define combine(a, b, c) {a = (c << 32) | a;} Where a is 64 bits and b and c are 32 bits. However, the compiler warns me about the fact that I'm shifting a 32 bit variable by 32 bits. My questions are these: what's bad about shifting a 32-bit variable 32 bits? I'm guessing it's undefined, but these macros do seem to be working. Also, would you suggest I go about this another way? As I said, I'm fairly familiar with C, but bitwise operators and the like still give me a headache.

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