I believe this is equivalent, and a bit faster:
a32=: 65536#. 65521| _1 0+ [:(+/ , {.) 65521| [:+/\. 1,~ a.i. |.
a32 'Wikipedia'
300286872
a32 'The quick brown fox jumps over the lazy dog'
1541148634
Thanks,
--
Raul
On Sun, Aug 24, 2014 at 4:05 AM, bill lam <[email protected]> wrote:
> Does anyone have a J-ish solution to adler32 checksum
> and avoid overflow to floating points ?
>
> 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.
>
> * https://www.ietf.org/rfc/rfc1950.txt
> * http://en.wikipedia.org/wiki/Adler-32
>
> direct translation to J
>
> adler32=: 3 : 0
> 's1 s2'=. 1 0
> for_a. a.i.y do.
> s1=. 65521 | s1 + a
> s2=. 65521 | s2 + s1
> end.
> s1 + 16 (33 b.) s2
> )
>
> test data:
>
> adler32 'Wikipedia'
> 300286872
>
> adler32 'The quick brown fox jumps over the lazy dog'
> 1541148634
>
> --
> regards,
> ====================================================
> GPG key 1024D/4434BAB3 2008-08-24
> gpg --keyserver subkeys.pgp.net --recv-keys 4434BAB3
> gpg --keyserver subkeys.pgp.net --armor --export 4434BAB3
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
