Attempting to understand different CRC implementations
This tutorial (also here, here, and here for those who will complain about link rot), in particular "10. A Slightly Mangled Table-Driven Implementation", explains well the optimization to avoid feeding an extra 32 zero bits at the end. The bottom line is that you feed the bits into the end...
CRC32 not calculating the right checksum?
You don't say what system you are doing this on, but you may need to open with "rb" instead of "r" to assure that there are no end-of-line translations on the read data. It is good practice to put that in anyway for portability and to document that you are...
How is PNG CRC calculated exactly?
You can find a complete implementation of the CRC calculation (and PNG encoding in general) in this public domain code: http://upokecenter.dreamhosters.com/articles/2011/04/png-image-encoder-in-c/ static uint[] crcTable; // Stores a running CRC (initialized with the CRC of "IDAT" string). When // you write this to the PNG, write as a big-endian value static...
CRC32 function with PL/pgSQL
You can create the function yourself, this is a working example for PostgreSQL 9.4 CREATE OR REPLACE FUNCTION crc32(text_string text) RETURNS bigint AS $$ DECLARE tmp bigint; i int; j int; byte_length int; binary_string bytea; BEGIN IF text_string = '' THEN RETURN 0; END IF; i = 0; tmp =...
CRC32 in C# fails
The problem here is that you are using the wrong datatype. I'm not familiar with the CRC32 algorithm so I googled to find http://sanity-free.org/12/crc32_implementation_in_csharp.html as a reference implementation. the first thing I noticed is that they are using uint instead of long. This makes sense as I'd assume the 32...
How can I calculate a CRC-32 on an NSData object in Objective C?
If _crc32 is undefined, then you most likely forgot to add libz.dylib to the linked frameworks and libraries. It should definitely be available. You add it by clicking on the project in the Project navigator, selecting the target and the tab General and then clicking on the plus sign at...
Arduino CRC32 Code Explanation searched
I wrote the code you're linking to, so I will attempt to answer your questions. Using ~0L. This is necessary because the algorithm works on 32-bit numbers, and the Arduino's code uses 16-bit numbers by default. The "L" suffix tells the compiler that the value is "long", so it does...
CRC32 of binary string/binary data in python
Ajay's answer is incorrect as it treats the binary data as a literal string - each 1 or 0 gets encoded into a separate byte. Assuming your data is binary from UTF-8 encoding or just bytes concatenated into a long string, you should instead do something like this: import binascii...
How to calculate CRC of a 64Bit DLL in Delphi?
There is absolutely no reason for CRC of a 32-bit DLL to behave differently to CRC of a 64-bit DLL. CRC simply works on a file as is. SIDE NOTE: The 32 in CRC32 has nothing to do with whether the app/dll or whatever is 32-bit. (You can run a...
How to implement zlib's crc32_combine() function in PHP?
I got the code working: <?php define('GF2_DIM', 32); function gf2_matrix_times($mat, $vec) { $i = 0; $sum = 0; while ($vec) { if ($vec & 1) { $sum ^= $mat[$i]; } $vec >>= 1; $i++; } return $sum; } function gf2_matrix_square(&$square, &$mat) { for ($n = 0; $n < GF2_DIM; $n++)...
How random is PHP pseudo random, of 4 bytes
No, this is not surprising, and there is nothing wrong with the random number generator. This is the birthday problem. With just 23 people in a room, the probability that two of them have the same birthday is 50%. This is perhaps counter-intuitive until you realize that there are 253...
Find hash/crc32 algorithm with known hash value and original value
python,algorithm,hash,crc,crc32
You can use CRC RevEng to search for CRCs. This one turns out to be easy, as it is a standard CRC: % ./reveng -w 32 -s 2630303a30323a39423a39333a34413a38342631323926315d2852c5 width=32 poly=0x04c11db7 init=0xffffffff refin=false refout=false xorout=0x00000000 check=0x0376e6e7 name="CRC-32/MPEG-2" % ./reveng -w 32 -s 2646463a46463a46463a46463a46463a46462631323826319546841e width=32 poly=0x04c11db7 init=0xffffffff refin=false refout=false xorout=0x00000000 check=0x0376e6e7 name="CRC-32/MPEG-2"...
CRC of concatenated input with known CRCs [duplicate]
Yes. You can see how in the implementation of crc32_combine() in zlib. It takes crc1, crc2, and len2, where len2 is the number of bytes in the block on which crc2 was calculated. It takes O(log(len2)) time. The combination can be repeated for following blocks. The approach is to continue...
Why using Generator polynomial like this x^8 +x^2 +x+1 for CRC-8?
crc,crc32,crc16,error-detection,crc64
The polynomial chosen determines the error detection capability of the CRC. This capability is measured in Hamming Distance, which is the minimum number of bit errors that can be introduced in the message while leaving the CRC unchanged. This would be a false positive, where the CRC says the message...
Fast CRC algorithm? [closed]
CRC implementations use tables for speed. They are not required. Here is a short CRC32 using either the Castagnoli polynomial (same one as used by the Intel crc32 instruction), or the Ethernet polynomial (same one as used in zip, gzip, etc.). #include <stddef.h> #include <stdint.h> /* CRC-32C (iSCSI) polynomial in...
C zlib crc32 and Python zlib crc32 doesn't match
There were problems in your original C and Python code snippets. As for your second C snippet, I haven't tried to compile it, but it's not portable since byte order within an int is platform-dependant. So it will give different results depending on the endianness of the CPU. One problem,...
crc32 calculating (i'm in despair)
At last, I've got the reciept. It took much time, but I reinvented it )) Share it with anyone, who need it: 1. Take first 4 bytes from message (if it less than 4 byte - add zeros). May be you will need to reflect bits in EVERY byte (I...
CRC32 with signed bytes in java
You need "L" at the end of all of your hex constants. Then I get 46d81382 as the result, which is close to, but a permutation of what you said is expected.
Crc32 C implementation - doesn't work
//typedef struct { // unsigned short xor; //} xor_context;//--> Not sure what part this plays in the code! void crc32_init(crc32_context *context) { context->crc = 0xFFFFFFFF; } void crc32_update(crc32_context *context, unsigned char byte) { uint32_t crc, mask; crc = context->crc; crc = crc ^ byte; for (int j = 7; j...
Java returning different CRC32 results on same string
update() is for incrementally calculating the checksum over a sequence of bytes. Your code calculates the crc32 over the concatentation of all the ciphertexts provided to update() on the same CRC32 object. Try c.reset() c.update(ciphertext); System.out.println("Now ciphertext = " + ciphertext + ", and CRC = " + c.getValue()); ...
Calculating CRC initial value instead of appending the CRC to payload
I've now programmed a solution for the above mentioned problem which was easier than I initially thought it would be. I found several articles about how one can forge a CRC. That means how to patch data that way that the calculated CRC value will have a predefined value. Using...
CRC32 not calculated right
Solution drawn from chat dicussion The CRC-32 algorithm being implemented is CRC-32 Ethernet (generator polynomial 0x04C11DB7). This CRC-32 requires: Being initialized with 0xFFFFFFFF. And being finalized by XORing with 0xFFFFFFFF. Therefore, you should remove the crc ^~ 0xFFFFFFFF statements within your function, pass 0xFFFFFFFF on your call to the function,...