Re: [PATCH v8 1/4] util/uuid: add a hash function

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Sep 08, 2023 at 05:47:40PM +0200, Albert Esteve wrote:
> 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>
> ---
>  include/qemu/uuid.h    |  2 ++
>  tests/unit/test-uuid.c | 27 +++++++++++++++++++++++++++
>  util/uuid.c            | 15 +++++++++++++++
>  3 files changed, 44 insertions(+)
> 
> diff --git a/include/qemu/uuid.h b/include/qemu/uuid.h
> index dc40ee1fc9..e24a1099e4 100644
> --- a/include/qemu/uuid.h
> +++ b/include/qemu/uuid.h
> @@ -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
> diff --git a/tests/unit/test-uuid.c b/tests/unit/test-uuid.c
> index c111de5fc1..aedc125ae9 100644
> --- a/tests/unit/test-uuid.c
> +++ b/tests/unit/test-uuid.c
> @@ -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();
>  }
> diff --git a/util/uuid.c b/util/uuid.c
> index b1108dde78..b366961bc6 100644
> --- a/util/uuid.c
> +++ b/util/uuid.c
> @@ -116,3 +116,18 @@ 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;
> +}
> +

whitespace error:

.git/rebase-apply/patch:85: new blank line at EOF.
+
warning: 1 line adds whitespace errors.




> -- 
> 2.41.0