[ovs-dev] [classifier-opt 23/28] util: New function popcount().

[Ben Pfaff]

On Tue, Jul 31, 2012 at 10:40:13AM -0700, Ethan Jackson wrote:
> Oh one more thing:
> 
> This seems like the kind of thing that's both easy to get wrong, and
> easy to unit test.  Does it make sense to add one?

Yes, I folded this in, thanks:

diff --git a/tests/library.at b/tests/library.at
index 70660a2..0765c3f 100644
--- a/tests/library.at
+++ b/tests/library.at
@@ -103,12 +103,14 @@ AT_CLEANUP
 m4_foreach(
   [testname],
   [[ctz],
+   [popcount],
    [log_2_floor],
    [bitwise_copy],
    [bitwise_zero],
    [bitwise_one],
    [bitwise_is_all_zeros]],
   [AT_SETUP([testname[()] function])
+   AT_KEYWORDS([testname])
    AT_CHECK([test-util testname], [0], [], [])
    AT_CLEANUP])
 
diff --git a/tests/test-util.c b/tests/test-util.c
index 71a7f21..b98fc79 100644
--- a/tests/test-util.c
+++ b/tests/test-util.c
@@ -26,6 +26,9 @@
 #include "random.h"
 #include "util.h"
 
+#undef NDEBUG
+#include <assert.h>
+
 static void
 check_log_2_floor(uint32_t x, int n)
 {
@@ -85,6 +88,59 @@ test_ctz(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
     check_ctz(0, 32);
 }
 
+static void
+shuffle(unsigned int *p, size_t n)
+{
+    for (; n > 1; n--, p++) {
+        unsigned int *q = &p[rand() % n];
+        unsigned int tmp = *p;
+        *p = *q;
+        *q = tmp;
+    }
+}
+
+static void
+check_popcount(uint32_t x, int n)
+{
+    if (popcount(x) != n) {
+        fprintf(stderr, "popcount(%#"PRIx32") is %d but should be %d\n",
+                x, popcount(x), n);
+        abort();
+    }
+}
+
+static void
+test_popcount(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
+{
+    unsigned int bits[32];
+    int i;
+
+    for (i = 0; i < ARRAY_SIZE(bits); i++) {
+        bits[i] = 1u << i;
+    }
+
+    check_popcount(0, 0);
+
+    for (i = 0; i < 1000; i++) {
+        uint32_t x = 0;
+        int j;
+
+        shuffle(bits, ARRAY_SIZE(bits));
+        for (j = 0; j < 32; j++) {
+            x |= bits[j];
+            check_popcount(x, j + 1);
+        }
+        assert(x == UINT32_MAX);
+
+        shuffle(bits, ARRAY_SIZE(bits));
+        for (j = 31; j >= 0; j--) {
+            x &= ~bits[j];
+            check_popcount(x, j);
+        }
+        assert(x == 0);
+    }
+}
+
 /* Returns the sum of the squares of the first 'n' positive integers. */
 static unsigned int
 sum_of_squares(int n)
@@ -282,6 +338,7 @@ test_follow_symlinks(int argc, char *argv[])
 
 static const struct command commands[] = {
     {"ctz", 0, 0, test_ctz},
+    {"popcount", 0, 0, test_popcount},
     {"log_2_floor", 0, 0, test_log_2_floor},
     {"bitwise_copy", 0, 0, test_bitwise_copy},
     {"bitwise_zero", 0, 0, test_bitwise_zero},