crc

I have a system with roughly a 100 million documents, and I'd like to keep track of their modifications between mirrors. In order to exchange information about modifications effectively, I want to send information about modified documents by days, not by each separate document. Something like this: [ 2012/03/26, cs26], [ 2012/03/25, cs25], [ 2012/03/24, cs24], ... where each cs is the checksum of timestamps of all documents created on a particular day. Now, the problem I'm running into is that I don't know of an algorithm that could "subtract" data from the checksum when a document is being

I am trying to find the crc that works with the following results. The byte string consists of 2 bytes (ie. 0xCE1E) and the crc is an single byte (ie. 0x03) byte crc CE1E 03 CE20 45 CE22 6F 0000 C0 0001 D4 FFFF 95 Can anyone help? First, 4 hex digits aren't 4 bytes. Since all your examples show 4 hex digits -- 2 bytes -- I'll assume you mean 2 bytes. There are only 65,536 distinct hash values, here's what you do. Execute the hash function for all 65,536 values from 0000 to FFFF. Tabulate the results. That table is the function. It maps input value to output value. While lame, it's always

zlib's crc32_combine() takes crcA, crcB, and lengthB to calculate crcAB. # returns crcAB crc32_combine(crcA, crcB, lenB) Using concepts from Mark Adler's awesome posts here and here I was able to produce crc32_trim_trailing.pl which takes crcAB, crcB, and lengthB to calculate crcA (I use this to peel off padding of a known length and value). # prints crcA perl crc32_trim_trailing.pl $crcAB $crcB $lenB Unfortunately, this uses the principles of the slow method described, where each null byte must be peeled off one at a time. It's slow, but is a good proof of concept. I've been working to make a

i want to calculate the CRC value for a file using 32-bit algorithm in C#.net.... Algorithm is straightforward (rewritten from c++) class Crc32 { public static uint CountCrc(byte[] pBuf) { // Table of CRC-32's of all single byte values uint[] crctab = new uint[] { 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,

In my code i need to calculate CRC-16 16 bit values for the HEX values stored as NSdata, below is the code snippet to calculate CRC-16 in c. void UpdateCRC(unsigned short int *CRC, unsigned char x) { // This function uses the initial CRC value passed in the first // argument, then modifies it using the single character passed // as the second argument, according to a CRC-16 polynomial // Arguments: // CRC -- pointer to starting CRC value // x -- new character to be processed // Returns: // The function does not return any values, but updates the variable // pointed to by CRC static int const

I'm working with a small FAT16 filesystem, and I want to generate CRC values for indidual XML files which store configuration information. In case the data changes or is corrupted, I want to be able to check the CRC to determine that the file is still in it's original state. The question is, how do I put the CRC value into the file, without changing the CRC value of the file itself? I can think of a couple solutions, but I think there must be a fairly standard solution for this issue. You could append the CRC value to the end of the file. Then, when computing the CRC value later for checking,