Re: Fix strverscmp

[Isaac Dunham <idunham@lavabit.com>]

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On Wed, 5 Dec 2012 21:26:40 -0500
Rich Felker <dalias@aerifal.cx> wrote:

> > I'm getting the idea that that may actually work...in which case my
> > last version is unneeded.
> > Except, it breaks here:
> > 00123
> > 001145 <-should be the lesser (the leading zeros)
> 
> Yes, I was unaware of the leading-zero semantics when I wrote that.
> See my revised email with a proposed algorithm.

Which is almost exactly the same as the method below:

> > OTOH, it could be done by recording the zero while walking up the chain:
> > /*NOT tested*/
> > while (*l && *r && l[0]==r[0]){
> > 	if (l[0]='0'){
> > 		nozero=1;
> 
> It can't set the flag unconditionally, only if the previous byte was
> not a digit. Otherwise, non-leading zeros would break handling of
> numeric differences.
Fortunately for us, that appears to be incorrect:
idunham@Caracal:~$ ./a.out jan012 jan0111
1
1
idunham@Caracal:~$ ./a.out jan0001 jan001
-1
-1
idunham@Caracal:~$ ./a.out 0001 001
-1
-1
idunham@Caracal:~$ ./a.out 001 0001
1
1
idunham@Caracal:~$ ./a.out 0012 00111
1
1
idunham@Caracal:~$ ./a.out 00012 00111
-1
-1
idunham@Caracal:~$ ./a.out 00120 00111
1
1

That's testing with the attached version.


-- 
Isaac Dunham <idunham@lavabit.com>

[-- Attachment #2: strvers.c --]
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#define _GNU_SOURCE
#define _XOPEN_SOURCE	700
#include <stdio.h>
#include <string.h>
#include <ctype.h>


int str_vers_cmp(const char *l, const char *r){
	int haszero=0;
	while (*l && *r && l[0]==r[0]){
		if (l[0]=='0'){
			haszero=0;
		} else if (!isdigit(l[0])) {
			haszero=1;
		}
		l++; r++;
	}
	if ((isdigit(l[0]) && isdigit(r[0]) ) && haszero) {
	//return the one with the longer substring of numbers
		int lenl=0, lenr=0, firstl=l[0], firstr=r[0];
		while (isdigit(l++[0]) ) {
			lenl++;
		}
		while (isdigit(r++[0]) ) {
			lenr++;
		}
		if (lenl==lenr) {
			return (firstl -  firstr);
		} else {
			return (lenl - lenr);
		}
	} else {
		return (l[0] -  r[0]);
	}
} 

int main(int argc, char **argv){
	printf("%d\n%d\n",str_vers_cmp(argv[1], argv[2]), strverscmp(argv[1], argv[2]));
}