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Questions tagged [crc]

Cyclic redundancy check. An error checking mechanism used for verifying data integrity in serial protocols.

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When is CRC more appropriate to use than MD5/SHA1?

When is it appropriate to use CRC for error detection versus more modern hashing functions such as MD5 or SHA1? Is the former easier to implement on embedded hardware?
Gili
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15 answers

What is the fastest hash algorithm to check if two files are equal?

What is the fastest way to create a hash function which will be used to check if two files are equal? Security is not very important. Edit: I am sending a file over a network connection, and will be sure that the file on both sides are equal
eflles
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What checksum algorithm should I use?

I'm building a system which needs to be able to find if blobs of bytes have been updated. Rather than storing the whole blob (they can be up to 5MBs), I'm thinking I should compute a checksum of it, store this and compute the same checksum a little…
Julien Genestoux
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7 answers

Function to Calculate a CRC16 Checksum

I'm working on a library to provide simple reliable communication over an RS232 or RS485 connection. Part of this code involves using a CRC16 checksum on the data to detect corruption from line noise. I've created a function to calculate a CRC16…
Jonathan Lamothe
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2 answers

Probability of collision when using a 32-bit hash

I have a 10-character string key field in a database. I've used CRC32 to hash this field, but I'm worrying about duplicates. Could somebody show me the probability of collision in this situation? P.S.: My string field is unique in the database. If…
nguyenngoc101
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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…
Robert Deml
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5 answers

How to use boost::crc?

I want to use boost::crc so that it works exactly like PHP's crc32() function. I tried reading the horrible documentation and many headaches later I haven't made any progress. Apparently I have to do something like: int GetCrc32(const string&…
Andreas Bonini
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10 answers

compute crc of file in python

I want to calculate the CRC of file and get output like: E45A12AC. Here's my code: #!/usr/bin/env python import os, sys import zlib def crc(fileName): fd = open(fileName,"rb") content = fd.readlines() fd.close() for eachLine in…
user203547
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How to calculate 32 bit CRC in Ruby on rails?

i want to calculate 32 bit CRC value for 'input field value" in Ruby on rails. need the sample code , please help me anyone.
Jeyavel
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Can CRC32(C) ever return to 0?

I'm wondering if CRC32 sum and CRC32C in particular ever return to 0? The simple answer would be "yes" given a large enough data set. However, I was wondering if there is any provisioning in CRC32C standard that would explicitly prevent this from…
dtoux
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Trying to reverse engineer a packet checksum/CRC/hash

I have an old, no longer manufactured electronic device with a serial port. I am trying to reverse engineer the data packet CRC/checksum/hash used in this device. Anyone with keen eyes, sharp math skills out there who might be able to crack this…
MSunstrum
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definitive CRC for C

Since CRC is so widely used, I'm surprised by having a hard time finding CRC implementations in C. Is there a "definitive" CRC calculation snippet/algorithm for C, that "everyone" uses? Or: is there a good CRC implementation somebody can vouch for,…
oyvind
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How to generate a CRC-16 from C#

I am trying to generate a CRC-16 using C#. The hardware I am using for RS232 requires the input string to be HEX. The screenshot below shows the correct conversion, For a test, I need 8000 to be 0xC061, however the C# method that generates CRC-16…
dynamicuser
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CRC Calculation Of A Mostly Static Data Stream

Background: I have a section of memory, 1024 bytes. The last 1020 bytes will always be the same. The first 4 bytes will change (serial number of a product). I need to calculate the CRC-16 CCITT (0xFFFF starting, 0x1021 mask) for the entire…
mblem22
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How could I guess a checksum algorithm?

Let's assume that I have some packets with a 16-bit checksum at the end. I would like to guess which checksum algorithm is used. For a start, from dump data I can see that one byte change in the packet's payload totally changes the checksum, so I…
dpavlin
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