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

[Ethan Jackson]

Awesome, thanks!

Ethan

On Tue, Aug 7, 2012 at 2:06 PM, Ben Pfaff <blp at nicira.com> wrote:
> 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},