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  • Adding to a bit array

    - by Martin
    In my program, I am using BitArrays to represent 160 bit numbers. I want to be able to add, subtract, increment and decrement these numbers, what is the algorithm for doing this? At the moment I'm not interested in multiplication and division, but I might be in the future so bonus points for that. I'm implementing in C#, but pseudocode is fine if you're not familiar with the language

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  • C/C++ efficient bit array

    - by aaa
    hi. Can you recommend efficient/clean way to manipulate arbitrary length bit array? right now I am using regular int/char bitmask, but those are not very clean when array length is greater than datatype length. std vector<bool> is not available for me. thanks

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  • Trying to install postgresql:i386 on 12.04 amd64

    - by tim jackson
    Due to some legacy 32 bit libraries being used in postgresql functions I need to get a 32 bit install of Postgresql on a 64 bit native system. But it seems like there is a problem with the multiarch not seeing all.debs as satisfying dependencies. uname -a: 3.8.0-29-generic #42-precise-Ubuntu SMP x86_64 dpkg --print-architecture: amd64 dpkg --print-foreign-architecture: i386 apt-get install postgresql-9.1: returns postgresql : Depends: postgresql-9.1 but it is nto going to be installed postgresql-9.1:i386 : Depends: postgresql-common:i386 but it is not installable Depends: ssl-cert:i386 but it is not installable Depends: locales:i386 but it is not installable etc .. But I have installed ssl-cert_1.0.28ubuntu0.1_all.deb and locales_..._all.deb andpostgresql-common is an all.deb Does anyone have experience installing 32 bit packages on 64 bit systems that depend on packages that are all.debs. Or has anyone installed 32 bit postgres on 64 bit? Any help appreciated.

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  • Learning C bit manipulation

    - by VaioIsBorn
    I didn't know any better name for a title of the question. For ex: on one of my previous questions one answered ((a)-(b))&0x80000000) 31 - this is kind of a too advanced for me and i can't really get what it means. I am not looking just for an answer of that, but i need someone to tell me some books/sites/whatever where i can learn this cool "advanced" tricks in C - and learn how and where to use them respectively too.

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  • bit ordering and endianess

    - by Neeraj
    I am reading a file byte-by-byte. Say for example i have this byte: 0x41 (0100 0001) represented in hex. Now, I want the first three bits of this byte, i.e (010). I can use bitwise logic to extract the first three bits, but my question is will the first three bits be independent of endianess of the machine.(i.e they can't be 001)? Thanks,

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  • ActiveX component can't create Object Error? Check 64 bit Status

    - by Rick Strahl
    If you're running on IIS 7 and a 64 bit operating system you might run into the following error using ASP classic or ASP.NET with COM interop. In classic ASP applications the error will show up as: ActiveX component can't create object   (Error 429) (actually without error handling the error just shows up as 500 error page) In my case the code that's been giving me problems has been a FoxPro COM object I'd been using to serve banner ads to some of my pages. The code basically looks up banners from a database table and displays them at random. The ASP classic code that uses it looks like this: <% Set banner = Server.CreateObject("wwBanner.aspBanner") banner.BannerFile = "wwsitebanners" Response.Write(banner.GetBanner(-1)) %> Originally this code had no specific error checking as above so the ASP pages just failed with 500 error pages from the Web server. To find out what the problem is this code is more useful at least for debugging: <% ON ERROR RESUME NEXT Set banner = Server.CreateObject("wwBanner.aspBanner") Response.Write(err.Number & " - " & err.Description) banner.BannerFile = "wwsitebanners" Response.Write(banner.GetBanner(-1)) %> which results in: 429 - ActiveX component can't create object which at least gives you a slight clue. In ASP.NET invoking the same COM object with code like this: <% dynamic banner = wwUtils.CreateComInstance("wwBanner.aspBanner") as dynamic; banner.cBANNERFILE = "wwsitebanners"; Response.Write(banner.getBanner(-1)); %> results in: Retrieving the COM class factory for component with CLSID {B5DCBB81-D5F5-11D2-B85E-00600889F23B} failed due to the following error: 80040154 Class not registered (Exception from HRESULT: 0x80040154 (REGDB_E_CLASSNOTREG)). The class is in fact registered though and the COM server loads fine from a command prompt or other COM client. This error can be caused by a COM server that doesn't load. It looks like a COM registration error. There are a number of traditional reasons why this error can crop up of course. The server isn't registered (run regserver32 to register a DLL server or /regserver on an EXE server) Access permissions aren't set on the COM server (Web account has to be able to read the DLL ie. Network service) The COM server fails to load during initialization ie. failing during startup One thing I always do to check for COM errors fire up the server in a COM client outside of IIS and ensure that it works there first - it's almost always easier to debug a server outside of the Web environment. In my case I tried the server in Visual FoxPro on the server with: loBanners = CREATEOBJECT("wwBanner.aspBanner") loBanners.cBannerFile = "wwsitebanners" ? loBanners.GetBanner(-1) and it worked just fine. If you don't have a full dev environment on the server you can also use VBScript do the same thing and run the .vbs file from the command prompt: Set banner = Server.CreateObject("wwBanner.aspBanner") banner.BannerFile = "wwsitebanners" MsgBox(banner.getBanner(-1)) Since this both works it tells me the server is registered and working properly. This leaves startup failures or permissions as the problem. I double checked permissions for the Application Pool and the permissions of the folder where the DLL lives and both are properly set to allow access by the Application Pool impersonated user. Just to be sure I assigned an Admin user to the Application Pool but still no go. So now what? 64 bit Servers Ahoy A couple of weeks back I had set up a few of my Application pools to 64 bit mode. My server is Server 2008 64 bit and by default Application Pools run 64 bit. Originally when I installed the server I set up most of my Application Pools to 32 bit mainly for backwards compatibility. But as more of my code migrates to 64 bit OS's I figured it'd be a good idea to see how well code runs under 64 bit code. The transition has been mostly painless. Until today when I noticed the problem with the code above when scrolling to my IIS logs and noticing a lot of 500 errors on many of my ASP classic pages. The code in question in most of these pages deals with this single simple COM object. It took a while to figure out that the problem is caused by the Application Pool running in 64 bit mode. The issue is that 32 bit COM objects (ie. my old Visual FoxPro COM component) cannot be loaded in a 64 bit Application Pool. The ASP pages using this COM component broke on the day I switched my main Application Pool into 64 bit mode but I didn't find the problem until I searched my logs for errors by pure chance. To fix this is easy enough once you know what the problem is by switching the Application Pool to Enable 32-bit Applications: Once this is done the COM objects started working correctly again. 64 bit ASP and ASP.NET with DCOM Servers This is kind of off topic, but incidentally it's possible to load 32 bit DCOM (out of process) servers from ASP.NET and ASP classic even if those applications run in 64 bit application pools. In fact, in West Wind Web Connection I use this capability to run a 64 bit ASP.NET handler that talks to a 32 bit FoxPro COM server which allows West Wind Web Connection to run in native 64 bit mode without custom configuration (which is actually quite useful). It's probably not a common usage scenario but it's good to know that you can actually access 32 bit COM objects this way from ASP.NET. For West Wind Web Connection this works out well as the DCOM interface only makes one non-chatty call to the backend server that handles all the rest of the request processing. Application Pool Isolation is your Friend For me the recent incident of failure in the classic ASP pages has just been another reminder to be very careful with moving applications to 64 bit operation. There are many little traps when switching to 64 bit that are very difficult to track and test for. I described one issue I had a couple of months ago where one of the default ASP.NET filters was loading the wrong version (32bit instead of 64bit) which was extremely difficult to track down and was caused by a very sneaky configuration switch error (basically 3 different entries for the same ISAPI filter all with different bitness settings). It took me almost a full day to track this down). Recently I've been taken to isolate individual applications into separate Application Pools rather than my past practice of combining many apps into shared AppPools. This is a good practice assuming you have enough memory to make this work. Application Pool isolate provides more modularity and allows me to selectively move applications to 64 bit. The error above came about precisely because I moved one of my most populous app pools to 64 bit and forgot about the minimal COM object use in some of my old pages. It's easy to forget. To 64bit or Not Is it worth it to move to 64 bit? Currently I'd say -not really. In my - admittedly limited - testing I don't see any significant performance increases. In fact 64 bit apps just seem to consume considerably more memory (30-50% more in my pools on average) and performance is minimally improved (less than 5% at the very best) in the load testing I've performed on a couple of sites in both modes. The only real incentive for 64 bit would be applications that require huge data spaces that exceed the 32 bit 4 gigabyte memory limit. However I have a hard time imagining an application that needs 4 gigs of memory in a single Application Pool :-). Curious to hear other opinions on benefits of 64 bit operation. © Rick Strahl, West Wind Technologies, 2005-2011Posted in COM   ASP.NET  FoxPro  

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  • Position of least significant bit that is set

    - by peterchen
    I am looking for an efficient way to determine the position of the least significant bit that is set in an integer, e.g. for 0x0FF0 it would be 4. A trivial implementation is this: unsigned GetLowestBitPos(unsigned value) { assert(value != 0); // handled separately unsigned pos = 0; while (!(value & 1)) { value >>= 1; ++pos; } return pos; } Any ideas how to squeeze some cycles out of it? (Note: this question is for people that enjoy such things, not for people to tell me xyzoptimization is evil.) [edit] Thanks everyone for the ideas! I've learnt a few other things, too. Cool!

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  • C/C++ - Convert 24-bit signed integer to float

    - by e-t172
    I'm programming in C++. I need to convert a 24-bit signed integer (stored in a 3-byte array) to float (normalizing to [-1.0,1.0]). The platform is MSVC++ on x86 (which means the input is little-endian). I tried this: float convert(const unsigned char* src) { int i = src[2]; i = (i << 8) | src[1]; i = (i << 8) | src[0]; const float Q = 2.0 / ((1 << 24) - 1.0); return (i + 0.5) * Q; } I'm not entirely sure, but it seems the results I'm getting from this code are incorrect. So, is my code wrong and if so, why?

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  • Bitwise operators versus .NET abstractions for bit manipulation in C# prespective

    - by Leron
    I'm trying to get basic skills in working with bits using C#.NET. I posted an example yesterday with a simple problem that needs bit manipulation which led me to the fact that there are two main approaches - using bitwise operators or using .NET abstractions such as BitArray (Please let me know if there are more build-in tools for working with bits other than BitArray in .NET and how to find more info for them if there are?). I understand that bitwise operators work faster but using BitArray is something much more easier for me, but one thing I really try to avoid is learning bad practices. Even though my personal preferences are for the .NET abstraction(s) I want to know which i actually better to learn and use in a real program. Thinking about it I'm tempted to think that .NET abstractions are not that bad at, after all there must be reason to be there and maybe being a beginner it's more natural to learn the abstraction and later on improve my skills with low level operations, but this is just random thoughts.

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  • Bit Flipping in Hex

    - by freyrs
    I have an 8 digit hexadecimal number of which I need certain digits to be either 0 or f. Given the specific place of the digits is there a quick way to generate the hex number with those places "flipped" to f. For example: flip_digits(1) = 0x000000f flip_digits(1,2,4) = 0x0000f0ff flip_digits(1,7,8) = 0xff00000f I'm doing this on an embedded device so I can't call any math libraries, I suspect it can be done with just bit shifts but I can't quite figure out the method. Any sort of solution (Python, C, Pseudocode) will work. Thanks in advance.

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  • Can I connect to a 64 bit mysql server from a 32 bit machine with 32 bit mysql client lib?

    - by chenqingzhi
    Can I connect to a 64 bit mysql server from a 32 bit machine with 32 bit mysql client lib? I mean the server is 64 bit version and running on an 64 bit machine and the client app is running on an 32 bit machine with the 32 bit mysql client lib. Is that OK? Or it will cause some problems? I don't have two machine so I can't do the test, can some tell me the answer? Thank you!

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  • Running 32 bit assembly code on a 64 bit Linux & 64 bit Processor : Explain the anomaly.

    - by claws
    Hello, I'm in an interesting problem.I forgot I'm using 64bit machine & OS and wrote a 32 bit assembly code. I don't know how to write 64 bit code. This is the x86 32-bit assembly code for Gnu Assembler (AT&T syntax) on Linux. //hello.S #include <asm/unistd.h> #include <syscall.h> #define STDOUT 1 .data hellostr: .ascii "hello wolrd\n"; helloend: .text .globl _start _start: movl $(SYS_write) , %eax //ssize_t write(int fd, const void *buf, size_t count); movl $(STDOUT) , %ebx movl $hellostr , %ecx movl $(helloend-hellostr) , %edx int $0x80 movl $(SYS_exit), %eax //void _exit(int status); xorl %ebx, %ebx int $0x80 ret Now, This code should run fine on a 32bit processor & 32 bit OS right? As we know 64 bit processors are backward compatible with 32 bit processors. So, that also wouldn't be a problem. The problem arises because of differences in system calls & call mechanism in 64-bit OS & 32-bit OS. I don't know why but they changed the system call numbers between 32-bit linux & 64-bit linux. asm/unistd_32.h defines: #define __NR_write 4 #define __NR_exit 1 asm/unistd_64.h defines: #define __NR_write 1 #define __NR_exit 60 Anyway using Macros instead of direct numbers is paid off. Its ensuring correct system call numbers. when I assemble & link & run the program. $cpp hello.S hello.s //pre-processor $as hello.s -o hello.o //assemble $ld hello.o // linker : converting relocatable to executable Its not printing helloworld. In gdb its showing: Program exited with code 01. I don't know how to debug in gdb. using tutorial I tried to debug it and execute instruction by instruction checking registers at each step. its always showing me "program exited with 01". It would be great if some on could show me how to debug this. (gdb) break _start Note: breakpoint -10 also set at pc 0x4000b0. Breakpoint 8 at 0x4000b0 (gdb) start Function "main" not defined. Make breakpoint pending on future shared library load? (y or [n]) y Temporary breakpoint 9 (main) pending. Starting program: /home/claws/helloworld Program exited with code 01. (gdb) info breakpoints Num Type Disp Enb Address What 8 breakpoint keep y 0x00000000004000b0 <_start> 9 breakpoint del y <PENDING> main I tried running strace. This is its output: execve("./helloworld", ["./helloworld"], [/* 39 vars */]) = 0 write(0, NULL, 12 <unfinished ... exit status 1> Explain the parameters of write(0, NULL, 12) system call in the output of strace? What exactly is happening? I want to know the reason why exactly its exiting with exitstatus=1? Can some one please show me how to debug this program using gdb? Why did they change the system call numbers? Kindly change this program appropriately so that it can run correctly on this machine. EDIT: After reading Paul R's answer. I checked my files claws@claws-desktop:~$ file ./hello.o ./hello.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped claws@claws-desktop:~$ file ./hello ./hello: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, not stripped All of my questions still hold true. What exactly is happening in this case? Can someone please answer my questions and provide an x86-64 version of this code?

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  • Bit reversal of an integer, ignoring integer size and endianness

    - by ??O?????
    Given an integer typedef: typedef unsigned int TYPE; or typedef unsigned long TYPE; I have the following code to reverse the bits of an integer: TYPE max_bit= (TYPE)-1; void reverse_int_setup() { TYPE bits= (TYPE)max_bit; while (bits <<= 1) max_bit= bits; } TYPE reverse_int(TYPE arg) { TYPE bit_setter= 1, bit_tester= max_bit, result= 0; for (result= 0; bit_tester; bit_tester>>= 1, bit_setter<<= 1) if (arg & bit_tester) result|= bit_setter; return result; } One just needs first to run reverse_int_setup(), which stores an integer with the highest bit turned on, then any call to reverse_int(arg) returns arg with its bits reversed (to be used as a key to a binary tree, taken from an increasing counter, but that's more or less irrelevant). Is there a platform-agnostic way to have in compile-time the correct value for max_int after the call to reverse_int_setup(); Otherwise, is there an algorithm you consider better/leaner than the one I have for reverse_int()? Thanks.

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  • Speed up bitstring/bit operations in Python?

    - by Xavier Ho
    I wrote a prime number generator using Sieve of Eratosthenes and Python 3.1. The code runs correctly and gracefully at 0.32 seconds on ideone.com to generate prime numbers up to 1,000,000. # from bitstring import BitString def prime_numbers(limit=1000000): '''Prime number generator. Yields the series 2, 3, 5, 7, 11, 13, 17, 19, 23, 29 ... using Sieve of Eratosthenes. ''' yield 2 sub_limit = int(limit**0.5) flags = [False, False] + [True] * (limit - 2) # flags = BitString(limit) # Step through all the odd numbers for i in range(3, limit, 2): if flags[i] is False: # if flags[i] is True: continue yield i # Exclude further multiples of the current prime number if i <= sub_limit: for j in range(i*3, limit, i<<1): flags[j] = False # flags[j] = True The problem is, I run out of memory when I try to generate numbers up to 1,000,000,000. flags = [False, False] + [True] * (limit - 2) MemoryError As you can imagine, allocating 1 billion boolean values (1 byte 4 or 8 bytes (see comment) each in Python) is really not feasible, so I looked into bitstring. I figured, using 1 bit for each flag would be much more memory-efficient. However, the program's performance dropped drastically - 24 seconds runtime, for prime number up to 1,000,000. This is probably due to the internal implementation of bitstring. You can comment/uncomment the three lines to see what I changed to use BitString, as the code snippet above. My question is, is there a way to speed up my program, with or without bitstring?

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  • SQL complex Question

    - by santanu
    Hello All, I need to find a function. the scenario is : I have 2 table. 1. news table 2. news_comment table need to find the most commented 20 news. the news_comment table has the relationship with the news table Thank you

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  • regex question: independent position of words

    - by Fuxi
    hi all, is it possible to define a regex pattern which checks eg. for 3 terms independent to their position in the main string? eg. my string is something like "click here to unsubscribe: http://www.url.com" the pattern should also work with "http:// unsubscribe click" thx

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  • Bit shift and pointer oddities in C, looking for explanations

    - by foo
    Hi all, I discovered something odd that I can't explain. If someone here can see what or why this is happening I'd like to know. What I'm doing is taking an unsigned short containing 12 bits aligned high like this: 1111 1111 1111 0000 I then want to shif the bits so that each byte in the short hold 7bits with the MSB as a pad. The result on what's presented above should look like this: 0111 1111 0111 1100 What I have done is this: unsigned short buf = 0xfff; //align high buf <<= 4; buf >>= 1; *((char*)&buf) >>= 1; This gives me something like looks like it's correct but the result of the last shift leaves the bit set like this: 0111 1111 1111 1100 Very odd. If I use an unsigned char as a temporary storage and shift that then it works, like this: unsigned short buf = 0xfff; buf <<= 4; buf >>= 1; tmp = *((char*)&buf); *((char*)&buf) = tmp >> 1; The result of this is: 0111 1111 0111 1100 Any ideas what is going on here?

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  • Returning a Value From the Bit.ly JS API Callback

    - by mtorbin
    Hey all, I am attempting to turn this "one shot" script into something more extensible. The problem is that I cannot figure out how to get the callback function to set a value outside of itself (please note that references to the Bit.ly API and the prototype.js frame work which are required have been left out due to login and apiKey information): CURRENTLY WORKING CODE var setShortUrl = function(data) { var resultOBJ, myURL; for(x in data.results){resultOBJ = data.results[x];} for(key in resultOBJ){if(key == "shortUrl"){myURL = resultOBJ[key];}} alert(myURL); } BitlyClient.shorten('http://www.thinkgeek.com', 'setShortUrl'); PROPOSED CHANGES var setShortUrl = function(data) { var resultOBJ, myURL; for(x in data.results){resultOBJ = data.results[x];} for(key in resultOBJ){if(key == "shortUrl"){myURL = resultOBJ[key];}} alert(myURL); return myURL; } var myTEST = BitlyClient.shorten('http://www.thinkgeek.com', 'setShortUrl'); alert(myTEST); As you can see this doesn't work the way I'm am expecting. If I could get a pointer in the right direction it would be most appreciated. Thanks, MT

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  • Free Fall Question

    - by Makenshi
    ok im gonna try my best to explain my problem i have this program where u can select 5 balls when u select one you can take it with you while you have the mouse button pressed and its within the ball radius. The problem is that i need a way to make the ball go up when the user stop pressing the mouse button like he sent it to float in the air then make it fall down again i have one way to know the time,velocity and thus the acceleration but i dont know how to implement it... right now i have this void Circulo::caida(float velocidad,float tiempo) { if(this->posY >= 580) { this->posY = 580; this->vcaida = 0.0f; } else if(this->posY < 580) { //this->distancia=9.81f * 0.5f*tiempo*tiempo; this->vcaida += velocidad; this->posY += this->vcaida; } } with this like this it just falls and i cant make the effect i tried to explain... thank you i hope someone can help me .< oh yeah im calculating the time like this just in case it helps difX=(x> evento.motion.xrel)? x-evento.motion.xrel : evento.motion.xrel-x; difY=(y> evento.motion.yrel)? y-evento.motion.yrel : evento.motion.yrel-y; and im sending difY as the time variable

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