See RFC1950:

ADLER32 (Adler-32 checksum) This contains a checksum value of the uncompressed data (excluding any dictionary data) computed according to Adler-32 algorithm. This algorithm is a 32-bit extension and improvement of the Fletcher algorithm, used in the ITU-T X.224 / ISO 8073 standard. See references [4] and [5] in Chapter 3, below)

Adler-32 is composed of two sums accumulated per byte: s1 is the sum of all bytes, s2 is the sum of all s1 values. Both sums are done modulo 65521. s1 is initialized to 1, s2 to zero. The Adler-32 checksum is stored as s2*65536 + s1 in most- significant-byte first (network) order. - Andreas----- Original Message ----- From: "ducasse" ducasse@iam.unibe.ch To: "The general-purpose Squeak developers list" squeak-dev@lists.squeakfoundation.org Sent: Wednesday, February 18, 2004 9:35 PM Subject: Re: [ENH][VM][TEST] Adler32 crc primitive

hi andreas

just for fun I was reading your changeset and the tests. Because I wanted to know if I could understand something from the tests. In 2 min this is not enough but this gives a really good impression.

By curiosity what means adler?

Stef

On 18 févr. 04, at 21:19, Andreas Raab wrote:

Looks like we need this ... at this point we're spending nearly half of the overall time for ZLibStream's compression/decompression in crc computations. The attached primitive should fix the problem and the tests should make sure it actually works :-) <Adler32Primitive.1.cs>