crc32

How do I calculate CRC32 of a string

How do I calculate the CRC32 (Cyclic Redundancy Checksum) of a string in .NET? ...

CRC32 C or C++ implementation

I'm looking for an implementation of CRC32 in C or C++ that is explicitly licensed as being free or public domain. The implementation here seems nice, but the only thing it says about the license is "source code", which isn't good enough. I'd prefer non LGPL so I don't have to fool around with a DLL (my app is closed source). I saw th...

Why is this CRC32 implementation in C# so slow?

I'm using the following function to compute the CRC32 of a file in a VS2008, .NET 3.5 project: public UInt32 ComputeHash(System.IO.Stream stream) { unchecked { const int BUFFER_SIZE = 1024; UInt32 crc32Result = 0xFFFFFFFF; byte[] buffer = new byte[BUFFER_SIZE]; int count = stream.Read(buffer, 0, ...

What is a running CRC?

I have searched and am not able to find information on what it is and how it is computed. ...

Creating zip using Zip Utility

Hi, I am using the Zip utility package of Java and wanted to know how to create a zip file with no compression at all. Setting the level to 0 doesn't help. Is this right? Also, when I used the 'STORED' method, it throws following exception: java.util.zip.ZipException: STORED entry missing size, compressed size, or crc-32 I can set ...

Hash function combining - is there a significant decrease in collision risk?

Hi all. Does anyone know if there's a real benefit regarding decreasing collision probability by combining hash functions? I especially need to know this regarding 32 bit hashing, namely combining Adler32 and CRC32. Basically, will adler32(crc32(data)) yield a smaller collision probability than crc32(data)? The last comment here gives so...

CRC32 to make short URL for web

I am trying to understand crc32 to generate the unique url for web page. If we use the crc32, what is the maximum number of urls can be used so that we can avoid duplicates? What could be the approximative string length to keep the checksum to be 2^32? When I tried UUID for an url and convert the uuid bytes to base 64, I could reduce ...

Efficient ways of telling whether or not a string/file has changed - crc32? md5? something else?

I'm looking for an efficient way to tell whether or not a string (or a file) has changed since the last time we looked at it. So, we run this function against 1,000,000 files/strings (each file/string is less than 1000 bytes), and store the output for each file/string. I'll then wait a few days and run this again. I need to find out ...

Reversing CRC32

I'm looking for a way to reverse a CRC32 checksum. There are solutions around, but they are either badly written, extremely technical and/or in Assembly. Assembly is (currently) beyond my ken, so I'm hoping someone can piece together an implementation in a higher level language. Ruby is ideal, but I can parse PHP, Python, C, Java, etc. ...

the fastest way to create checksum for large files in python

hi, i need to transfer large files across network and need to create checksum for them on hourly basis. so the speed for generating checksum is critical for me. somehow i can't make zlib.crc32 and zlib.adler32 working with files larger than 4GB on Windows XP Pro 64bit machine. i suspect i've hit the 32bit limitation here? using hashlib...

.net 3.5:how to implement calculate crc32 for data using dot net 3.5 api?

how to implement calculate crc32 for data using dot net 3.5 api.I have done the same in java with following code. public static String getMAC (byte [] value) { java.util.zip.CRC32 crc32 = new java.util.zip.CRC32 (); crc32.update(value); long newCRC = crc32.getValue(); String crcString = Long.toHexString(newCRC); ...

is there any better algorithm of crc32 to check corruption of data?

i am receiving packets from a terminal device and then upon receiving packets on host side, i use crc32 algo to generate mac for packet data so that i can check is there any corruption of data during transfer of packet from terminal to host.Is crc32 reliable for this purpose or is there some better algorithm? ...

Dot net 3.5: does dot net 3.5 provides some api to calculate crc32 for input data?

Does dot net 3.5 provides some api to calculate crc32 for input data?I have got some links which provides source code to do so.But i want to use Dot Net Api's code. ...

C# fast crc32 calculation :

I've profiled my application with Ants and found out that > 10% is in CRC32 calculations. (The CRC32-calculation is done in plain C#) I did some googling and learned about the following intrinsics in Visual Studio 2008 : _mm_crc32_u8 _mm_crc32_u16 _mm_crc32_u32 _mm_crc32_u64 ( http://msdn.microsoft.com/en-us/library/bb514036.aspx )...

hw to get source code native c language library of java 1.4?

Hi i want to see implementation of java.util.zip.CRC32. But within this class its using native c library functions for core implementation.How can I get the native source code. I can see the java.util.zip.CRC32 source code, but this doesn't have the actual implementation. ...

Data Length vs CRC Length

I've seen 8-bit, 16-bit, and 32-bit CRCs. At what point do I need to jump to a wider CRC? My gut reaction is that it is based on the data length: 1-100 bytes: 8-bit CRC 101 - 1000 bytes: 16-bit CRC 1001 - ??? bytes: 32-bit CRC EDIT: Looking at the Wikipedia page about CRC and Lott's answer, here' what we have: <64 bytes: 8-bit CRC...

PHP crc32() only numbers

I have a MD5 hash: 10f86782177490f2ac970b8dc4c51014 http://www.fileformat.info/tool/hash.htm?text=10f86782177490f2ac970b8dc4c51014 Result: c74e16d9 but PHP: crc32('10f86782177490f2ac970b8dc4c51014'); Result: -951183655 I don't understand! ...

CRC for PNG file format

Hi All, I need to read a PNG file and interpret all the information stored in it and print it in human readable format. While working on PNG, i understood that it uses CRC-32 for generating checksum for each chunk. But I could not understand the following information mentioned on the PNG file specification site: The polynomial used by P...

How is a CRC32 checksum calculated?

Maybe I'm just not seeing it, but CRC32 seems either needlessly complicated, or insufficiently explained anywhere I could find on the web. I understand the gist of it is that it is the remainder from a non-carry based arithmitic division of the message value, divided by the polynomial, but the actual implementation of it escapes me. I'...

crc32 decrypt short string

I am retrieving lists of crc32 hashes that contain names of files, not there contents. I need to be able to decrypt the strings which are hashed names like "vacationplans_2010.txt" which are less then 25 characters long. is this possible? ...