Re: strverscmp

[Isaac Dunham <idunham@lavabit.com>]

[-- Attachment #1: Type: text/plain, Size: 2347 bytes --]

On Sun, 17 Feb 2013 13:39:44 -0500
Rich Felker <dalias@aerifal.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@lavabit.com>

[-- Attachment #2: strverscmp.diff --]
[-- Type: text/x-diff, Size: 927 bytes --]

diff --git a/src/string/strverscmp.c b/src/string/strverscmp.c
index 7054967..33a42ee 100644
--- a/src/string/strverscmp.c
+++ b/src/string/strverscmp.c
@@ -1,7 +1,40 @@
+#define _GNU_SOURCE
+#include <ctype.h>
 #include <string.h>
+#include <sys/types.h>
 
 int strverscmp(const char *l, const char *r)
 {
-	/* FIXME */
-	return strcmp(l, r);
+	int haszero=1;
+	while (*l==*r) {
+		if (!*l) return 0;
+
+		if (*l=='0') {
+			if (haszero==1) {
+				haszero=0;
+			}
+		} else if (isdigit(*l)) {
+			if (haszero==1) {
+				haszero=2;
+			}
+		} else {
+			haszero=1;
+		}
+		l++; r++;
+	}
+	if (haszero==1 && (*l=='0' || *r=='0')) {
+		haszero=0;
+	}
+	if ((isdigit(*l) && isdigit(*r) ) && haszero) {
+		size_t lenl=0, lenr=0;
+		while (isdigit(l[lenl]) ) lenl++;
+		while (isdigit(r[lenr]) ) lenr++;
+		if (lenl==lenr) {
+			return (*l -  *r);
+		} else {
+			return (lenl - lenr);
+		}
+	} else {
+		return (*l -  *r);
+	}
 }