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Message-Id: <20130218171558.bf161621.idunham@lavabit.com>
Date: Mon, 18 Feb 2013 17:15:58 -0800
From: Isaac Dunham <idunham@...abit.com>
To: musl@...ts.openwall.com
Subject: Re: strverscmp
On Sun, 17 Feb 2013 13:39:44 -0500
Rich Felker <dalias@...ifal.cx> wrote:
>
> Hey, sorry it's taken me so long to get to reading and reviewing this
> well. Here are some comments, mostly stylistic, but one's about a
> corner-case bug. See below. With that said, the algorithm looks right
> to me, and I think we can commit soon.
>
> Rich
All the comments seem like improvements to me.
Attached is a revised version.
> > + while (*l && *r && l[0]==r[0]){
>
> I used to do a lot of while loops like this, but now I feel like it
> makes it hard to follow the end-of-string logic -- a lot more code
> runs after the null terminator is hit, and it's nontrivial to follow
> through it all and make sure the right thing happens, as the
> subsequent code after the loop is now handling two very-distinct
> loop-exit conditions:
>
> 1. Loop exited due to mismatch.
> 2. Loop exited due to hitting end-of-string with no mismatch.
>
> What about instead doing something like this:
>
> while (*l==*r) {
> if (!*l) return 0;
> /* ... */
>
> That way, the "equal strings" case is trivially correct. It also might
> generate better code.
OK.
> Note that I also made a couple stylistic changes here; unless you
> object, I prefer *p to p[0] when p is just being used as a moving
> pointer within a string, always accessed with offset 0. It's just more
> concise/less cluttered and avoids suggesting it's used as a string in
> itself. Also added a space before the open brace, for consistency with
> style elsewhere.
<snip>
> > + if ((isdigit(l[0]) && isdigit(r[0]) ) && haszero) {
> > + int lenl=0, lenr=0, firstl=l[0], firstr=r[0];
>
> These variables have the wrong types. int is not sufficient to store a
> character count in a string. You need size_t.
>
> > + while (isdigit(l++[0]) ) {
> > + lenl++;
> > + }
> > + while (isdigit(r++[0]) ) {
> > + lenr++;
> > + }
> > + if (lenl==lenr) {
> > + return (firstl - firstr);
> > + } else {
> > + return (lenl - lenr);
> > + }
>
> I see what's going on here, but I find saving the first mismatching
> characters (btw, you could have just saved the difference) then
> continuing to advance the l/r pointers a bit confusing at first. Why
> not instead do:
>
> while (isdigit(l[lenl])) lenl++;
That would be clearer and more efficient.
--
Isaac Dunham <idunham@...abit.com>
View attachment "strverscmp.diff" of type "text/x-diff" (928 bytes)
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