crc32 gives incorrect checksum when seed is 0

[DonBrinn]

Consider the following:

const {crc32} = require('crc');
> crc32([1], 0);
2298007401
> crc32([1], undefined);
2768625435

A seed value of 0 should be treated the same as no seed value (i.e seed value undefined).

2768625435 is the value that should be returned from the call to crc32([1], 0).

[alexgorbatchev]

Hi @DonBrinn, I believe this is the expected behavior. The default initial value for CRC32 is 0xFFFFFFFF, which is -1. This could be verified over at http://www.sunshine2k.de/coding/javascript/crc/crc_js.html for example. CRC32 of helloworld is 0xF9EB20AD with default CRC32 Initial Value of 0xFFFFFFFF. Changing initial value to 0 produces 0xE59EB724.

I've also verified this with Ruby:

require 'zlib'

puts("no initial value   : #{(Zlib::crc32('helloworld')).to_s(16)}")
puts("with initial value : #{Zlib::crc32('world', Zlib::crc32('hello')).to_s(16)}")
>
no initial value   : f9eb20ad
with initial value : f9eb20ad

The same output is produced by node-crc CRC32 function:

const together = crc32(Buffer.from('helloworld'));
let separately = crc32(Buffer.from('hello'));
separately = crc32(Buffer.from('world'), separately);
expect(separately).to.equal(together);

console.log({
  crc: crc32.model,
  together: together.toString(16),
  separately: separately.toString(16),
});
>
{ crc: 'crc-32', together: 'f9eb20ad', separately: 'f9eb20ad' }