a question about netlink?

From: æå(çä çå)
Date: Thu Dec 16 2010 - 22:29:09 EST

in af_netlink.c

do_one_broadcast
{
ÂÂÂÂÂÂÂÂ if (nlk->pid == p->pid || p->group - 1 >= nlk->ngroups ||
ÂÂÂÂÂÂÂÂ ÂÂÂ !test_bit(p->group - 1, nlk->groups))
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ goto out;
}

why here write:" p->group - 1 >= nlk->ngroups" but not " p->group > nlk->ngroups " , or " (p->group & nlk->ngroups) != 0 "

I think the message is only sento nlk whoes groups 'p->group' bit is set.
èº{.nÇ+‰·Ÿ®‰­†+%ŠËlzwm…ébëæìr¸›zX§»®w¥Š{ayºÊÚë,j­¢f£¢·hš‹àz¹®w¥¢¸ ¢·¦j:+v‰¨ŠwèjØm¶Ÿÿ¾«‘êçzZ+ƒùšŽŠÝj"ú!¶iO•æ¬z·švØ^¶m§ÿðà nÆàþY&—