PERL Beginners - Re: Help understanding VEC

Author

Re: Help understanding VEC

Tom Phoenix

2006-03-26, 9:57 pm

On 3/26/06, Jim <jkipp5@comcast.net> wrote:

> I am trying to understand how vec() is works in the code below

Have you seen the documentation in the perlfunc manpage?

perldoc -f vec

If you still have questions, after seeing the docs, please ask again.
Hope this helps!

--Tom Phoenix
Stonehenge Perl Training

Jim

2006-03-27, 7:57 am

>
>
> Have you seen the documentation in the perlfunc manpage?
>
> perldoc -f vec
>
> If you still have questions, after seeing the docs, please ask again.
> Hope this helps!
>

Yes, I have read it already. Thanks

John W. Krahn

2006-03-27, 6:57 pm

Jay Savage wrote:
>
> Treats the string in EXPR as a bit vector made up of elements of width
> BITS, and returns the value of the element specified by OFFSET as an
> unsigned integer.
>
> You might also want to keep in mind that the BITS must be a power of 1

It must be a power of 2.

> from one to 32, and that vec() is lvaluable, but you don't need to
> know that to look at the code here.
>
> vec( $address, 7, 1 )
>
> sayas "break up the string $address into chunks of one bit, and return
> the seventh chunk". Then it looks at the 6th chunk and the 5th chunk.

It is zero based so that is "the eighth chunk" followed by the 7th chunk and
the 6th chunk.

> The sneaky part was stringing all those tertiary "hook" operators
> together; that's probably the confusing part. John, or whoever wrote
> the code,

Guilty.

[snip]

> Why this works has to do with the way different classes of networks
> are assigned, and the way struct in_addr is defined in socket.h. For
> more information on the various standard ways hostnames and inet
> address are assigned and described, pick up a book on tcp/ip.

Or read: ftp://ftp.rfc-editor.org/in-notes/rfc1166.txt and
ftp://ftp.rfc-editor.org/in-notes/rfc1918.txt

Although classes have been mostly superseded by Classless Inter-Domain Routing
ftp://ftp.rfc-editor.org/in-notes/rfc1517.txt
ftp://ftp.rfc-editor.org/in-notes/rfc1518.txt
ftp://ftp.rfc-editor.org/in-notes/rfc1519.txt
ftp://ftp.rfc-editor.org/in-notes/rfc1520.txt

John
--
use Perl;
program
fulfillment

Chad Perrin

2006-03-27, 6:57 pm

On Mon, Mar 27, 2006 at 04:17:41PM -0800, John W. Krahn wrote:
> Jay Savage wrote:
>
> It must be a power of 2.

.. . . and thus a power of 10.

Ahem.

--
Chad Perrin [ CCD CopyWrite | http://ccd.apotheon.org ]
This sig for rent: a Signify v1.14 production from http://www.debian.org/

Jim

2006-03-27, 9:57 pm

> Jay Savage wrote:
>
> power of 1
>
[color=darkred]
>
> and return
> 5th chunk.
>
[color=darkred]
>
> whoever wrote

Thanks John and Jay. It was the way the operators fell falls through. I
worked it out again and now understand it.

[color=darkred]
> socket.h. .....

I knew exactly what the goal of the code was and how class and classless
networks and subnetting works. This question was more about understanding
vec()

Thanks again

Jay Savage

2006-03-28, 3:57 am

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