CRC32 or something like that in JUCE?

Feature Requests
1

Just wondering if there’s a CRC32 function or similar in JUCE already. Couldn’t find anything, and the forum search also didn’t give me anything I could use.

The idea is to take a MemoryBlock and create some check-number that I can compare with another number to be sure that the file is not corrupted.

EG: piano_sound.sound - at the end of the file I add the CRC32 number, and load everything BUT that number into the MemoryBlock. Now I create the CRC32 from the memory block and check if both matches.

Cheers, WilliamK

2

Another option would add a parity bit to the stream, but that will make the file much larger. But at the same time, it will be easier and faster to load, I think…

3

There is one in ZipFile you could check out.

Rail

4

MD5, SHA-256, or Whirlpool?

https://docs.juce.com/master/group__juce__cryptography-hashing.html

Matt

5

Thanks guys, I forgot to search for MD5…

6

anyone know what flags to use to access the crc32 functions? seem to be undefined by default

7

Sorry to dig this up but it’s one of the very few topics about CRC on this forum and I think my version might help people searching for this.

So just FYI, this is the CRC32 function I use:

static uint32_t calculateCRC32(const juce::Array<uint32_t>& data) {
	uint32_t crc = 0xFFFFFFFF; // initial vector
	for (uint32_t d : data) {
		crc = crc ^ d;
		for (int j = 31; j >= 0; j--) {
			uint32_t mask = (uint32_t)(-((int32_t)(crc & 1)));
			crc = (crc >> 1) ^ (0xEDB88320 & mask); // polynomial is 0x04C11DB7
		}
	}
	return crc; // not ~crc as we used the JAMCRC variant with XorOut cancelled
}

It’s the typical CRC-32 but the JAMCRC variant, i.e. Poly = 0x04C11DB7, Init = 0xFFFFFFFF, RefIn = true, RefOut = true, XorOut = 0

So it’s the same as this in PHP, for example: $crc = crc32($data) ^ 0xFFFFFFFF;

See https://crccalc.com/ for more info

To get the “normal” CRC (not the JAMCRC variant), simply change the last line to return ~crc;.