I’m leery of aperkins solution (since deleted), but I know why it worked. The line (which has since been corrected in his answer) zipOut.setLevel(ZipOutputStream.STORED); // accidentally right was using the static value ZipOutputStream.STORED, which coincidentally equals 0. So what that line is doing is setting the level used by the default DEFLATED method to zero … Read more
You could use Ruby’s Zlib module. require ‘zlib’ crc32 = Zlib::crc32(‘input field value’)
Revisited, August 2014 Prompted by Arnaud Bouchez in a recent comment, and in view of other answers and comments, I acknowledge that the original answer needs to be altered or for the least qualified. I left the original as-is, at the end, for reference. First, and maybe most important, a fair answer to the question … Read more
Here are both software and hardware versions of CRC-32C. The software version is optimized to process eight bytes at a time. The hardware version is optimized to run three crc32q instructions effectively in parallel on a single core, since the throughput of that instruction is one cycle, but the latency is three cycles. crc32c.c: /* … Read more
Python 2 (unlike py3) is doing a signed 32-bit CRC. Those sites are doing an unsigned 32-bit CRC. The values are the same otherwise, as you can see from this: >>> 0x100000000 – 0xb1d4025b == 0x4e2bfda5 True One quick way to convert from 32-bit signed to 32-bit unsigned is:* >>> -1311505829 % (1<<32) 2983461467 Or, … Read more
Update I added a helper function to create the CRCTable instead of having this enormous literal in the code. It could also be used to create the table once and save it in an object or variable and have the crc32 function use that (or as W3C’s example, check for the existence and create if … Read more
CRC32 works very well as a hash algorithm. The whole point of a CRC is to hash a stream of bytes with as few collisions as possible. That said, there are a few points to consider: CRC’s are not secure. For secure hashing you need a much more computationally expensive algorithm. Different CRC flavors exist … Read more
It’s not a research topic. It’s really well understood: http://en.wikipedia.org/wiki/Cyclic_redundancy_check The math is pretty simple. An 8-bit CRC boils all messages down to one of 256 values. If your message is more than a few bytes long, the possibility of multiple messages having the same hash value goes up higher and higher. A 16-bit CRC, … Read more
This guy seems to have your answer. https://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net And in case the blog ever goes away or breaks the url, here’s the github link: https://github.com/damieng/DamienGKit/blob/master/CSharp/DamienG.Library/Security/Cryptography/Crc32.cs Usage of the Crc32 class from the blog post: Crc32 crc32 = new Crc32(); String hash = String.Empty; using (FileStream fs = File.Open(“c:\\myfile.txt”, FileMode.Open)) foreach (byte b in crc32.ComputeHash(fs)) hash … Read more
The SNIPPETS C Source Code Archive has a CRC32 implementation that is freely usable: /* Copyright (C) 1986 Gary S. Brown. You may use this program, or code or tables extracted from it, as desired without restriction.*/ (Unfortunately, c.snippets.org seems to have died. Fortunately, the Wayback Machine has it archived.) In order to be able … Read more