linux-kernel - Re: [PATCH] lib/vsprintf: add %pT[C012] format specifier

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Date:	Wed, 01 Jan 2014 17:33:09 -0800
From:	Joe Perches <joe@...ches.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	akpm@...ux-foundation.org, geert@...ux-m68k.org, jkosina@...e.cz,
	viro@...iv.linux.org.uk, davem@...emloft.net,
	keescook@...omium.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/vsprintf: add %pT[C012] format specifier

On Wed, 2014-01-01 at 19:02 +0900, Tetsuo Handa wrote:
> Joe Perches wrote:
> > > This choice (i.e. reserve only '\xFF') is more resource economy than my
> > > previous choice (i.e. reserve '\x7F' to '\xFF') at the cost of wasting only
> > > one byte compared to my previous choice.
> > 
> > I supposed that's better.
> > 
> > Is there a particularly utility/reason to use 0xff
> > vs ascii SUB/PU1/PU2?
> > 
> Nothing. Is 0x1A preferable to 0xFF?

ASCII SUB seems to me to fit better for the purpose.
The "Private Use" PU1/PU2 also seemed appropriate,
but I suppose any non-printable character might be OK.

(from wikipedia)

The substitute character (SUB) was intended to request a translation of
the next character from a printable character to another value, usually
by setting bit 5 to zero. This is handy because some media (such as
sheets of paper produced by typewriters) can transmit only printable
characters. However, on MS-DOS systems with files opened in text mode,
"end of text" or "end of file" is marked by this Ctrl-Z character,
instead of the Ctrl-C or Ctrl-D, which are common on other operating
systems.

PU1/PU2:

Reserved for a function without standardized meaning for private use as
required, subject to the prior agreement of the sender and the recipient
of the data.

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