lldp: simplify compare_func, using ?: to chain comparisons

The ?: operator is very useful for chaining comparison functions
(strcmp, memcmp, CMP), since its behavior is to return the result
of the comparison function call if non-zero, or continue evaluating
the chain of comparison functions.

This simplifies the code in that using a temporary `r` variable
to store the function results is no longer necessary and the checks
for non-zero to return are no longer needed either, resulting in a
typical three-fold reduction to the number of lines in the code.

Introduce a new memcmp_nn() to compare two memory buffers in
lexicographic order, taking length in consideration.

Tested: $ ninja -C build/ test

All test cases pass. In particular, test_multiple_neighbors_sorted()
in test-lldp would catch regressions introduced by this commit.

diff --git a/src/basic/util.h b/src/basic/util.h
index 85a7a15843c8dc9009e661cd27030c0d22d8a847..f009d37d4c6f1a9a03f8c14557a3478a98eccb3c 100644 (file)
--- a/src/basic/util.h
+++ b/src/basic/util.h
@@ -147,6 +147,12 @@ static inline int memcmp_safe(const void *s1, const void *s2, size_t n) {
         return memcmp(s1, s2, n);
 }
 
+/* Compare s1 (length n1) with s2 (length n2) in lexicographic order. */
+static inline int memcmp_nn(const void *s1, size_t n1, const void *s2, size_t n2) {
+        return memcmp_safe(s1, s2, MIN(n1, n2))
+            ?: CMP(n1, n2);
+}
+
 int on_ac_power(void);
 
 #define memzero(x,l)                                            \

diff --git a/src/libsystemd-network/lldp-neighbor.c b/src/libsystemd-network/lldp-neighbor.c
index 952197e714930992c292e2fa7a732b87bd116aac..199d8aee0ac4300e379e4370224777a559b41efa 100644 (file)
--- a/src/libsystemd-network/lldp-neighbor.c
+++ b/src/libsystemd-network/lldp-neighbor.c
@@ -9,6 +9,7 @@
 #include "lldp-neighbor.h"
 #include "missing.h"
 #include "unaligned.h"
+#include "util.h"
 
 static void lldp_neighbor_id_hash_func(const LLDPNeighborID *id, struct siphash *state) {
         siphash24_compress(id->chassis_id, id->chassis_id_size, state);
@@ -18,21 +19,8 @@ static void lldp_neighbor_id_hash_func(const LLDPNeighborID *id, struct siphash
 }
 
 int lldp_neighbor_id_compare_func(const LLDPNeighborID *x, const LLDPNeighborID *y) {
-        int r;
-
-        r = memcmp(x->chassis_id, y->chassis_id, MIN(x->chassis_id_size, y->chassis_id_size));
-        if (r != 0)
-                return r;
-
-        r = CMP(x->chassis_id_size, y->chassis_id_size);
-        if (r != 0)
-                return r;
-
-        r = memcmp(x->port_id, y->port_id, MIN(x->port_id_size, y->port_id_size));
-        if (r != 0)
-                return r;
-
-        return CMP(x->port_id_size, y->port_id_size);
+        return memcmp_nn(x->chassis_id, x->chassis_id_size, y->chassis_id, y->chassis_id_size)
+            ?: memcmp_nn(x->port_id, x->port_id_size, y->port_id, y->port_id_size);
 }
 
 DEFINE_HASH_OPS_WITH_VALUE_DESTRUCTOR(lldp_neighbor_hash_ops, LLDPNeighborID, lldp_neighbor_id_hash_func, lldp_neighbor_id_compare_func,