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util/uuid: add a hash function 

Add hash function to uuid module using the
djb2 hash algorithm.

Add a couple simple unit tests for the hash
function, checking collisions for similar UUIDs.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
Message-Id: <20231002065706.94707-2-aesteve@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Albert Esteve 2023-10-02 08:57:03 +02:00 committed by Michael S. Tsirkin
parent 70f88436aa
commit a6ceee591a
3 changed files with 43 additions and 0 deletions
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2
include/qemu/uuid.h
View File

@ -96,4 +96,6 @@ int qemu_uuid_parse(const char *str, QemuUUID *uuid);
QemuUUID qemu_uuid_bswap(QemuUUID uuid);
uint32_t qemu_uuid_hash(const void *uuid);
#endif

27
tests/unit/test-uuid.c
View File

@ -171,6 +171,32 @@ static void test_uuid_unparse_strdup(void)
}
}
static void test_uuid_hash(void)
{
QemuUUID uuid;
int i;
for (i = 0; i < 100; i++) {
qemu_uuid_generate(&uuid);
/* Obtain the UUID hash */
uint32_t hash_a = qemu_uuid_hash(&uuid);
int data_idx = g_random_int_range(0, 15);
/* Change a single random byte of the UUID */
if (uuid.data[data_idx] < 0xFF) {
uuid.data[data_idx]++;
} else {
uuid.data[data_idx]--;
}
/* Obtain the UUID hash again */
uint32_t hash_b = qemu_uuid_hash(&uuid);
/*
* Both hashes shall be different (avoid collision)
* for any change in the UUID fields
*/
g_assert_cmpint(hash_a, !=, hash_b);
}
}
int main(int argc, char **argv)
{
g_test_init(&argc, &argv, NULL);
@ -179,6 +205,7 @@ int main(int argc, char **argv)
g_test_add_func("/uuid/parse", test_uuid_parse);
g_test_add_func("/uuid/unparse", test_uuid_unparse);
g_test_add_func("/uuid/unparse_strdup", test_uuid_unparse_strdup);
g_test_add_func("/uuid/hash", test_uuid_hash);
return g_test_run();
}

14
util/uuid.c
View File

@ -116,3 +116,17 @@ QemuUUID qemu_uuid_bswap(QemuUUID uuid)
bswap16s(&uuid.fields.time_high_and_version);
return uuid;
}
/* djb2 hash algorithm */
uint32_t qemu_uuid_hash(const void *uuid)
{
QemuUUID *qid = (QemuUUID *) uuid;
uint32_t h = 5381;
int i;
for (i = 0; i < ARRAY_SIZE(qid->data); i++) {
h = (h << 5) + h + qid->data[i];
}
return h;
}