I'm looking for an implementation of CRC32 in C or C++ that is explicitly licensed as being no cost 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 the adler32 implementation in zlib, but I'm checking small chunks of data, which adler is not good for.
9 Answers
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 to compile the code, you'll need to add typedefs for BYTE as an unsigned 8-bit integer and DWORD as an unsigned 32-bit integer, along with the header files crc.h & sniptype.h.
The only critical item in the header is this macro (which could just as easily go in CRC_32.c itself:
#define UPDC32(octet, crc) (crc_32_tab[((crc) ^ (octet)) & 0xff] ^ ((crc) >> 8))
I am the author of the source code at the specified link. While the intention of the source code license is not clear (it will be later today), the code is in fact open and free for use in your free or commercial applications with no strings attached.
The mhash library works pretty good for me. It's fast enough, supports multiple types of hashing (crc32, MD5, SHA-1, HAVAL, RIPEMD128, RIPEMD160, TIGER, GOST, etc.). To get CRC32 of a string you would do something like this:
MHASH td = mhash_init(MHASH_CRC32);
if (td == MHASH_FAILED) return -1; // handle failure
mhash(td, s, strlen(s));
unsigned int digest = 0; // crc32 will be stored here
mhash_deinit(td, &digest);
// do endian swap here if desired
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