util: New macros ROUND_UP_POW2, ROUND_DOWN_POW2.

Signed-off-by: Ben Pfaff <blp@nicira.com>

diff --git a/lib/util.h b/lib/util.h
index ae8bfd7..2159594 100644 (file)
--- a/lib/util.h
+++ b/lib/util.h
@@ -108,6 +108,25 @@ is_pow2(uintmax_t x)
     return IS_POW2(x);
 }
 
+/* Returns X rounded up to a power of 2.  X must be a constant expression. */
+#define ROUND_UP_POW2(X) RUP2__(X)
+#define RUP2__(X) (RUP2_1(X) + 1)
+#define RUP2_1(X) (RUP2_2(X) | (RUP2_2(X) >> 16))
+#define RUP2_2(X) (RUP2_3(X) | (RUP2_3(X) >> 8))
+#define RUP2_3(X) (RUP2_4(X) | (RUP2_4(X) >> 4))
+#define RUP2_4(X) (RUP2_5(X) | (RUP2_5(X) >> 2))
+#define RUP2_5(X) (RUP2_6(X) | (RUP2_6(X) >> 1))
+#define RUP2_6(X) ((X) - 1)
+
+/* Returns X rounded down to a power of 2.  X must be a constant expression. */
+#define ROUND_DOWN_POW2(X) RDP2__(X)
+#define RDP2__(X) (RDP2_1(X) - (RDP2_1(X) >> 1))
+#define RDP2_1(X) (RDP2_2(X) | (RDP2_2(X) >> 16))
+#define RDP2_2(X) (RDP2_3(X) | (RDP2_3(X) >> 8))
+#define RDP2_3(X) (RDP2_4(X) | (RDP2_4(X) >> 4))
+#define RDP2_4(X) (RDP2_5(X) | (RDP2_5(X) >> 2))
+#define RDP2_5(X) (      (X) | (      (X) >> 1))
+
 #ifndef MIN
 #define MIN(X, Y) ((X) < (Y) ? (X) : (Y))
 #endif

diff --git a/tests/library.at b/tests/library.at
index 541a416..ded0a22 100644 (file)
--- a/tests/library.at
+++ b/tests/library.at
@@ -112,6 +112,8 @@ AT_CLEANUP
 m4_foreach(
   [testname],
   [[ctz],
+   [round_up_pow2],
+   [round_down_pow2],
    [popcount],
    [log_2_floor],
    [bitwise_copy],

diff --git a/tests/test-util.c b/tests/test-util.c
index 5afe2f7..6bf8ed5 100644 (file)
--- a/tests/test-util.c
+++ b/tests/test-util.c
@@ -90,6 +90,69 @@ test_ctz(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
     check_ctz(0, 32);
 }
 
+/* Returns a random number in the range 'min'...'max' inclusive. */
+static uint32_t
+random_in_range(uint32_t min, uint32_t max)
+{
+    return min == max ? min : min + random_range(max - min + 1);
+}
+
+static void
+check_rup2(uint32_t x, int n)
+{
+    uint32_t rup2 = ROUND_UP_POW2(x);
+    if (rup2 != n) {
+        fprintf(stderr, "ROUND_UP_POW2(%#"PRIx32") is %#"PRIx32" "
+                "but should be %#"PRIx32"\n", x, rup2, n);
+        abort();
+    }
+}
+
+static void
+test_round_up_pow2(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
+{
+    int n;
+
+    for (n = 0; n < 32; n++) {
+        /* Min, max value for which ROUND_UP_POW2 should yield (1 << n). */
+        uint32_t min = ((1u << n) >> 1) + 1;
+        uint32_t max = 1u << n;
+
+        check_rup2(min, 1u << n);
+        check_rup2(max, 1u << n);
+        check_rup2(random_in_range(min, max), 1u << n);
+    }
+    check_rup2(0, 0);
+}
+
+static void
+check_rdp2(uint32_t x, int n)
+{
+    uint32_t rdp2 = ROUND_DOWN_POW2(x);
+    if (rdp2 != n) {
+        fprintf(stderr, "ROUND_DOWN_POW2(%#"PRIx32") is %#"PRIx32" "
+                "but should be %#"PRIx32"\n", x, rdp2, n);
+        abort();
+    }
+}
+
+static void
+test_round_down_pow2(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
+{
+    int n;
+
+    for (n = 0; n < 32; n++) {
+        /* Min, max value for which ROUND_DOWN_POW2 should yield (1 << n). */
+        uint32_t min = 1u << n;
+        uint32_t max = ((1u << n) << 1) - 1;
+
+        check_rdp2(min, 1u << n);
+        check_rdp2(max, 1u << n);
+        check_rdp2(random_in_range(min, max), 1u << n);
+    }
+    check_rdp2(0, 0);
+}
+
 static void
 shuffle(unsigned int *p, size_t n)
 {
@@ -346,6 +409,8 @@ test_assert(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
 \f
 static const struct command commands[] = {
     {"ctz", 0, 0, test_ctz},
+    {"round_up_pow2", 0, 0, test_round_up_pow2},
+    {"round_down_pow2", 0, 0, test_round_down_pow2},
     {"popcount", 0, 0, test_popcount},
     {"log_2_floor", 0, 0, test_log_2_floor},
     {"bitwise_copy", 0, 0, test_bitwise_copy},