GNU bug report logs - #16578
Wish: Support for non-native endianness in od

Previous Next

Full log

View this message in rfc822 format

From: nisse <at> lysator.liu.se (Niels Möller)
To: Pádraig Brady <P <at> draigBrady.com>
Cc: 16578-done <at> debbugs.gnu.org
Subject: bug#16578: Wish: Support for non-native endianness in od
Date: Sun, 09 Feb 2014 09:42:23 +0100

Pádraig Brady <P <at> draigBrady.com> writes:

> Attached in the patch I intend to push in your name.

Nice.

> I also added docs to usage() and the texinfo file, and added a test.

I don't quite understand how the test works, but as far as I see, it
doesn't test floats? So that's inconsistent with the commit message.

> BTW I checked if there was any speed difference with the new code.
> I wasn't expecting this to be a bottleneck, and true enough
> there is only a marginal change. The new code is consistently
> a little _faster_ though on my i3-2310M which is a bit surprising.

Odd. But performance of x86 is usually pretty hard to predict by just
looking at the source or assembly code. I was hoping that in the
non-swapped case, the false conditional

   if (input_swap && sizeof(T) > 1)

should be very friendly to the branch predictor, and hence almost free.

Jim Meyering <jim <at> meyering.net> writes:

> One nit: please change the type of "j" here (identical in attached)
> to be unsigned, to match that of the upper bound.

Makes sense. In my own projects, I tend to use unsigned int for loop
counts whereever I don't need to iterate over any negative values. But
my impression is that most others prefer to use signed int for
everything which doesn't rely on mod 2^n arithmetic, so that's why I
made j signed here.

> That would be our first use of "rev". Is it ubiquitous enough to depend on?

It appears *not* to be available on my closest solaris box. While on my
gnu/linux system, it's provided by util-linux. For the test, I guess rev
could be implemented something like

while read line
  printf "%s" line | tr -d '\n' | sed 's/./.\n/' | tac | tr -d '\n'
  echo
done 

Maybe rev should be provided by coreutils, similarly to tac? I'd prefer
not to think about the unicode issues for rev, though...

Regards,
/Niels

-- 
Niels Möller. PGP-encrypted email is preferred. Keyid C0B98E26.
Internet email is subject to wholesale government surveillance.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.