linux-kernel - Re: [PATCH 1/2] string: simplify stricmp()

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Date:	Fri, 22 Jan 2010 17:47:36 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	André Goddard Rosa <andre.goddard@...il.com>,
	linux-kernel@...r.kernel.org, Joe Perches <joe@...ches.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 1/2] string: simplify stricmp()

On Fri, 22 Jan 2010, Andrew Morton wrote:
> 
> hm, that function seems a little broken.
> 
> If it reaches the end of s1 or s2 it will return (c1 - c2).  If however
> it detects a difference due to other than end-of-string, it returns
> (tolower(c1) - tolower(c2)).
> 
> IOW, perhaps it should be performing tolower() in the
> I-reached-end-of-string case.

No, it doesn't matter. It's like strcmp - it returns "positive, negative 
or zero" depending on whether the string compared bigger than, smaller 
than or equal.

So "(int)c1 - (int)c2" is just a way to do that. And if the string ends 
and c1 or c2 is NUL, there's no point in doing the "tolower()", because it 
doesn't matter what the other character is: the sign is all that matters 
(or, if they are equally long, and both c1 and c2 are zero, then 0).

> I wonder what strnicmp() is _supposed_ to return..

Same as strncmp.

We could make it always return -1/0/+1 (many libraries do that - then the 
return value is guaranteed to also fit in a 'char', not just an 'int'), 
but it really shouldn't matter for any correct caller.

		Linus
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