util: New function log_2_floor().

Calculates the position of the most significant bit in a 32 bit
word.

3 files changed, 60 insertions, 0 deletions

diff --git a/tests/automake.mk b/tests/automake.mk
index be09b4a6..33307ccc 100644
--- a/tests/automake.mk
+++ b/tests/automake.mk
@@ -297,6 +297,10 @@ tests_test_strtok_r_SOURCES = tests/test-strtok_r.c
 noinst_PROGRAMS += tests/test-type-props
 tests_test_type_props_SOURCES = tests/test-type-props.c
 
+noinst_PROGRAMS += tests/test-util
+tests_test_util_SOURCES = tests/test-util.c
+tests_test_util_LDADD = lib/libopenvswitch.a
+
 noinst_PROGRAMS += tests/test-uuid
 tests_test_uuid_SOURCES = tests/test-uuid.c
 tests_test_uuid_LDADD = lib/libopenvswitch.a
diff --git a/tests/library.at b/tests/library.at
index ec50e23a..ca5f29ca 100644
--- a/tests/library.at
+++ b/tests/library.at
@@ -100,6 +100,10 @@ nibble   0   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15
 ])
 AT_CLEANUP
 
+AT_SETUP([test log_2_floor])
+AT_CHECK([test-util])
+AT_CLEANUP
+
 AT_SETUP([test unix socket -- short pathname])
 AT_CHECK([test-unix-socket x])
 AT_CLEANUP
diff --git a/tests/test-util.c b/tests/test-util.c
new file mode 100644
index 00000000..e9a827a4
--- /dev/null
+++ b/tests/test-util.c
@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2011 Nicira Networks.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "random.h"
+#include "util.h"
+
+static void
+check(uint32_t x, int n)
+{
+    if (log_2_floor(x) != n) {
+        fprintf(stderr, "log_2_floor(%"PRIu32") is %d but should be %d\n",
+                x, log_2_floor(x), n);
+        abort();
+    }
+}
+
+int
+main(void)
+{
+    int n;
+
+    for (n = 0; n < 32; n++) {
+        /* Check minimum x that has log2(x) == n. */
+        check(1 << n, n);
+
+        /* Check maximum x that has log2(x) == n. */
+        check((1 << n) | ((1 << n) - 1), n);
+
+        /* Check a random value in the middle. */
+        check((random_uint32() & ((1 << n) - 1)) | (1 << n), n);
+    }
+    return 0;
+}