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libalias: Fix splay comparsion bug

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Comparing elements in a tree requires transitiviy.  If a < b and b < c
then a must be smaller than c.  This way the tree elements are always
pairwise comparable.

Tristate comparsion functions returning values lower, equal, or
greater than zero, are usually implemented by a simple subtraction of
the operands.  If the size of the operands are equal to the size of
the result, integer modular arithmetics kick in and violates the
transitivity.

Example:
Working on byte with 0, 120, and 240. Now computing the differences:
  120 -   0 = 120
  240 - 120 = 120
  240 -   0 = -16

MFC after:	3 days
This commit is contained in:
Lutz Donnerhacke 2021-07-02 23:41:25 +02:00
parent dc35484536
commit 25392fac94
1 changed files with 7 additions and 6 deletions
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13
sys/netinet/libalias/alias_db.h
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@ -351,10 +351,10 @@ static inline int
cmp_out(struct alias_link *a, struct alias_link *b) {
int i = a->src_port - b->src_port;
if (i != 0) return (i);
i = a->src_addr.s_addr - b->src_addr.s_addr;
if (i != 0) return (i);
i = a->dst_addr.s_addr - b->dst_addr.s_addr;
if (i != 0) return (i);
if (a->src_addr.s_addr > b->src_addr.s_addr) return (1);
if (a->src_addr.s_addr < b->src_addr.s_addr) return (-1);
if (a->dst_addr.s_addr > b->dst_addr.s_addr) return (1);
if (a->dst_addr.s_addr < b->dst_addr.s_addr) return (-1);
i = a->dst_port - b->dst_port;
if (i != 0) return (i);
i = a->link_type - b->link_type;
@ -368,8 +368,9 @@ cmp_in(struct group_in *a, struct group_in *b) {
if (i != 0) return (i);
i = a->link_type - b->link_type;
if (i != 0) return (i);
i = a->alias_addr.s_addr - b->alias_addr.s_addr;
return (i);
if (a->alias_addr.s_addr > b->alias_addr.s_addr) return (1);
if (a->alias_addr.s_addr < b->alias_addr.s_addr) return (-1);
return (0);
}
SPLAY_PROTOTYPE(splay_in, group_in, in, cmp_in);