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core: implement nm_utils_ip4_netmask_to_prefix() via __builtin_ctz()

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Taken from systemd's in4_addr_netmask_to_prefixlen().

Yes, this adds the requirement that "int" is 32 bits. But systemd
already has the same requirement in u32ctz(), hence we anyway cannot
build on other architectures. If that is ever necessary, it's easy
to adjust.
This commit is contained in:
Thomas Haller
2018-12-14 16:45:53 +01:00
parent 8586ebb745
commit e442e3881e
2 changed files with 44 additions and 26 deletions
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29
libnm-core/nm-utils.c
View File

@@ -1389,30 +1389,13 @@ nm_utils_ip4_routes_from_variant (GVariant *value)
guint32 guint32
nm_utils_ip4_netmask_to_prefix (guint32 netmask) nm_utils_ip4_netmask_to_prefix (guint32 netmask)
{ {
guint32 prefix; G_STATIC_ASSERT_EXPR (__SIZEOF_INT__ == 4);
guint8 v; G_STATIC_ASSERT_EXPR (sizeof (int) == 4);
const guint8 *p = (guint8 *) &netmask; G_STATIC_ASSERT_EXPR (sizeof (netmask) == 4);
if (p[3]) { return ( (netmask != 0)
prefix = 24; ? (32 - __builtin_ctz (ntohl (netmask)))
v = p[3]; : 0);
} else if (p[2]) {
prefix = 16;
v = p[2];
} else if (p[1]) {
prefix = 8;
v = p[1];
} else {
prefix = 0;
v = p[0];
}
while (v) {
prefix++;
v <<= 1;
}
return prefix;
} }
/** /**

41
libnm-core/tests/test-general.c
View File

@@ -3468,6 +3468,41 @@ test_connection_changed_cb (NMConnection *connection, gboolean *data)
*data = TRUE; *data = TRUE;
} }
static guint32
_netmask_to_prefix (guint32 netmask)
{
guint32 prefix;
guint8 v;
const guint8 *p = (guint8 *) &netmask;
if (p[3]) {
prefix = 24;
v = p[3];
} else if (p[2]) {
prefix = 16;
v = p[2];
} else if (p[1]) {
prefix = 8;
v = p[1];
} else {
prefix = 0;
v = p[0];
}
while (v) {
prefix++;
v <<= 1;
}
g_assert_cmpint (prefix, <=, 32);
/* we re-implemented the netmask-to-prefix code differently. Check
* that they agree. */
g_assert_cmpint (prefix, ==, nm_utils_ip4_netmask_to_prefix (netmask));
return prefix;
}
static void static void
test_ip4_prefix_to_netmask (void) test_ip4_prefix_to_netmask (void)
{ {
@@ -3475,7 +3510,7 @@ test_ip4_prefix_to_netmask (void)
for (i = 0; i<=32; i++) { for (i = 0; i<=32; i++) {
guint32 netmask = _nm_utils_ip4_prefix_to_netmask (i); guint32 netmask = _nm_utils_ip4_prefix_to_netmask (i);
int plen = nm_utils_ip4_netmask_to_prefix (netmask); int plen = _netmask_to_prefix (netmask);
g_assert_cmpint (i, ==, plen); g_assert_cmpint (i, ==, plen);
{ {
@@ -3505,7 +3540,7 @@ test_ip4_netmask_to_prefix (void)
guint32 netmask = _nm_utils_ip4_prefix_to_netmask (i); guint32 netmask = _nm_utils_ip4_prefix_to_netmask (i);
guint32 netmask_lowest_bit = netmask & ~_nm_utils_ip4_prefix_to_netmask (i-1); guint32 netmask_lowest_bit = netmask & ~_nm_utils_ip4_prefix_to_netmask (i-1);
g_assert_cmpint (i, ==, nm_utils_ip4_netmask_to_prefix (netmask)); g_assert_cmpint (i, ==, _netmask_to_prefix (netmask));
for (j = 0; j < 2*i; j++) { for (j = 0; j < 2*i; j++) {
guint32 r = g_rand_int (rand); guint32 r = g_rand_int (rand);
@@ -3519,7 +3554,7 @@ test_ip4_netmask_to_prefix (void)
/* create an invalid netmask with holes and check that the function /* create an invalid netmask with holes and check that the function
* returns the longest prefix. */ * returns the longest prefix. */
prefix_holey = nm_utils_ip4_netmask_to_prefix (netmask_holey); prefix_holey = _netmask_to_prefix (netmask_holey);
g_assert_cmpint (i, ==, prefix_holey); g_assert_cmpint (i, ==, prefix_holey);
} }