J32 should give a 32-bit integer so that the last train
should be
[: ({: (23 b.) 16&(33 b.)@{.)
instead of
65536#.
This shoud be good enough. Thanks.
Вс, 24 авг 2014, Jan-Pieter Jacobs написал(а):
> You could incorporate the modulo operation in the summation directly:
>
> As per Raul's solution, with the modulo addition:
>
> a32_2=: 65536#. _1 0+ [:((65521|+)/ , {.) [: (65521|+)/\. 1,~ a.i. |.
> NB. Test on 10M of random data
> Randdata =: a.{~ ?10000000$256
> timespacex 'r1=:a32_2 Randdata'
> 7.26671 2.68438e8
>
> timespacex 'r1=:adler32 Randdata'
> 36.2094 2.01333e8
>
> Jan-Pieter
>
> 2014-08-24 11:14 GMT+02:00 bill lam <[email protected]>:
> > Since s2 is quadratic, it overflows quickly in J32. However
> > ieee floating points have 52 bits mantissa, so it can still
> > give correct result for medium size data albeit overflowed.
> >
> > 9!:11[16
> > (3!:0;]) a32 1e6{.a.
> >
> > Вс, 24 авг 2014, Raul Miller написал(а):
> >> Hmm... actually there might be a floating point overflow problem for
> >> gigabyte length arguments. I do not have the patience, however, to
> >> find what (for example) adler32 1e9#{:a. is.
> >>
> >> Thanks,
> >>
> >> --
> >> Raul
> >>
> >>
> >>
> >> On Sun, Aug 24, 2014 at 4:37 AM, Raul Miller <[email protected]> wrote:
> >> > 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
> >
> > --
> > 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
--
regards,
====================================================
GPG key 1024D/4434BAB3 2008-08-24
gpg --keyserver subkeys.pgp.net --recv-keys 4434BAB3
gpg --keyserver subkeys.pgp.net --armor --export 4434BAB3
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