Re: mgetgroups improvements

[Pádraig Brady]

Eric Blake wrote:
> According to Pádraig Brady on 12/4/2009 6:20 PM:
>>> +  /* Remove pair-wise duplicates, as well as any duplicate of the
>> ? +     first element.  Rather than do a full O(n log n) duplicate
>>> +     removal, this only visits the most common duplicates.  */
>> Why does the first element get extra checks.
>> Is it more likely to be duplicated?
> 
> Yes, for two reasons.  One, we pre-insert an arbitrary gid_t to the front..
> Two, some OS's actually list the effective gid twice, once at the front..

Ah OK, a comment along those lines would be useful.

> 
>>> +  {
>>> +    gid_t first = *g;
>>> +    gid_t *next;
>>> +    gid_t *last = g + ng;
>>> +
>>> +    for (next = g + 1; next < last; next++)
>> Should that be <=
> 
> No.  The array is indexed from 0, so last is one past the end of the
> array.  The iteration over next starts at element 1 (if there are at least
> two elements), because we trivially know that element 0 is equal to element 0.

:) May I suggest this comment.
gid_t *last = g + ng; /* sentinel after the last element */

cheers,
Pádraig.