unpack and endianness
Larry Wall
:
: Is there any way to specify the endiannes of the data you are
: unpacking? I am writing a perl script to decode Moria save files (for
: unspecified purposes :) and unfortunately for me the data is written
: in Intel order (LSB first). I can not use unpack (as far as I know)
: on the data from our Suns (MSB first). If I could get unpack to
: perform the byte shuffling for me it would squish my code by a factor
: of two.
: Does anyone know how to do this?
:
: Could it be as simple as
:
: read(STDIN, $_, 2*2);
: ($exp, $maxexp) = unpack("s-2", $_);
There's no way to do this with unpack on a big-endian machine at the moment.
The best you can do, as far as I can see, is to say
sub swab {
$_[0] =~ s/([\0-\377])([\0-\377])/$2$1/g;
}
read(STDIN, $_, 2*2);
&swab($_);
($exp, $maxexp) = unpack("s2", $_);
: Also, what is the filehandle for <>, I hate having to type
: "moriainterp.perl < moria.dc".
It's ARGV, but you can't do a read() on it and keep the other semantics of <>.
You want something more like open(STDIN,shift).
Larry
Cameron Simpson,foo
| In article <THOTH.90O...@reef.cis.ufl.edu> th...@reef.cis.ufl.edu (Gilligan) writes:
| :Is there any way to specify the endiannes of the data you are unpacking?
|
| The best you can do, as far as I can see, is to say
| sub swab {
| $_[0] =~ s/([\0-\377])([\0-\377])/$2$1/g;
| }
Um, why can't I write
sub swab {
$_[0] =~ s/(.)(.)/$2$1/g;
}
- Cameron Simpson, cam...@spectrum.cs.unsw.oz.au
Larry Wall
: From article <98...@jpl-devvax.JPL.NASA.GOV>, by lw...@jpl-devvax.JPL.NASA.GOV (Larry Wall):
: | sub swab {
: | $_[0] =~ s/([\0-\377])([\0-\377])/$2$1/g;
: | }
: [...]
:
: Um, why can't I write
: sub swab {
: $_[0] =~ s/(.)(.)/$2$1/g;
Because . doesn't match \n. [\0-\377] is the most efficient way to match
everything currently. Maybe \e should match everything.
And \E would of course match nothing. :-)
Larry
Cameron Simpson,foo
| In article <8...@usage.csd.unsw.oz.au> cam...@spectrum.cs.unsw.oz.au (Cameron Simpson) writes:
| : From article <98...@jpl-devvax.JPL.NASA.GOV>, by lw...@jpl-devvax.JPL.NASA.GOV (Larry Wall):
| :
|
| Because . doesn't match \n.
Goes back and Rs the FM more closely. Oh the embarrassment.
| [\0-\377] is the most efficient way to match
| everything currently. Maybe \e should match everything.
Nah. What's wrong with [^]?
| And \E would of course match nothing. :-)
Correspondingly, []. Haven't tried it yet (does so). Ouch. The ] at the
start of the pattern is taken as part of the range. A feature. Well, it
was a nice idea...
- Cameron Simpson
cam...@spectrum.cs.unsw.oz.au
"To every problem there is a simple, obvious, wrong solution."
Dan Bernstein
> From article <98...@jpl-devvax.JPL.NASA.GOV>, by lw...@jpl-devvax.JPL.NASA.GOV (Larry Wall):
> | everything currently. Maybe \e should match everything.
> Nah. What's wrong with [^]?
How do you specify ] in a [^...] expression, then? You mention the same
problem with []...
---Dan
Dale Worley
X-Name: Cameron Simpson,foo
Um, why can't I write
sub swab {
$_[0] =~ s/(.)(.)/$2$1/g;
}
Basically, because it doesn't work. This swaps every pair of bytes,
but doesn't swap the byte pairs, etc. The goal is to turn ABCD into
DCBA.
Dale Worley Compass, Inc. wor...@compass.com
--
The great unsolved problem of feminsm is to decide whether we need to
make men more like women, or women more like men.
Dale Lancaster
>Because . doesn't match \n. [\0-\377] is the most efficient way to match
>everything currently. Maybe \e should match everything.
>And \E would of course match nothing. :-)
>Larry
I would rather see \* match everything and \e be ESC as it is in
other utilities. And maybe \!* matches nothing? :-)
dml
Mark D. Baushke
Dale> In <98...@jpl-devvax.JPL.NASA.GOV> lw...@jpl-devvax.JPL.NASA.GOV
Dale> (Larry Wall) writes:
>Because . doesn't match \n. [\0-\377] is the most efficient way to match
>everything currently. Maybe \e should match everything.
>And \E would of course match nothing. :-)
>Larry
Dale> I would rather see \* match everything and \e be ESC as it is in
Dale> other utilities. And maybe \!* matches nothing? :-)
Dale> dml
Please do not create any non-alphanumeric metacharacters. It would
break the quoting of a pattern that might contain metacharacters using
$pattern =~ s/(\W)/\\$1/g;
--
Mark D. Baushke
m...@ESD.3Com.COM
Cimarron D. Taylor </>
| From: da...@convex.com (Dale Lancaster)
| Newsgroups: comp.lang.perl
| Subject: Re: unpack and endianness
| Date: 9 Oct 90 17:20:43 GMT
|
| I would rather see \* match everything and \e be ESC as it is in
|
But doesn't \* already mean "turn off the special meaning of *".
i.e. match only an asterix?
Cimarron Taylor
Electronics Research Laboratory / POSTGRES project
University of California, Berkeley
cima...@postgres.berkeley.edu
Larry Wall
'Sides, there's millions of scripts out there that already use \* to mean
a literal *.
And \e doesn't mean ESC to me, it means \. What utilities does it mean
ESC in? /etc/termcap uses \E, which is close.
I HAVE considered making \a mean \007 (since K&R2 has it), but there's
gotta be a limit somewhere.
[Strange, that never stopped you before.]
Oh, shaddap!
Larry
Eric Peterson
| And \e doesn't mean ESC to me, it means \. What utilities does it mean
| ESC in? /etc/termcap uses \E, which is close.
Well, GNU Emacs does this, if you can call something its size a
"utility" :-)
Eric
--
Eric Peterson <> epet...@encore.com <> uunet!encore!epeterson
Encore Computer Corp. * Ft. Lauderdale, Florida * (305) 587-2900 x 5208
Why did Constantinople get the works? Gung'f abobql'f ohfvarff ohg gur Ghexf.
Dan Mick
> But doesn't \* already mean "turn off the special meaning of *".
> i.e. match only an asterix?
What's an asterix? Why would you want perl to match a cartoon character?