[ovs-dev] [murmurhash 2/4] hash: Correct implementation of mhash_finish().

Ethan Jackson ethan at nicira.com
Tue Jan 15 21:21:37 UTC 2013


How did you notice this problem? Did the hash unit tests catch it?  If
not, could we extend them in some way so that they would?

Acked-by: Ethan Jackson <ethan at nicira.com>


On Fri, Dec 14, 2012 at 4:33 PM, Ben Pfaff <blp at nicira.com> wrote:
> With rotates instead of shifts, the upper and lower 16 bits of the returned
> hash are always the same.
>
> Signed-off-by: Ben Pfaff <blp at nicira.com>
> ---
>  lib/hash.h |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/lib/hash.h b/lib/hash.h
> index 701e686..96866c4 100644
> --- a/lib/hash.h
> +++ b/lib/hash.h
> @@ -152,11 +152,11 @@ static inline uint32_t mhash_add(uint32_t hash, uint32_t data)
>  static inline uint32_t mhash_finish(uint32_t hash, size_t n)
>  {
>      hash ^= n * 4;
> -    hash ^= hash_rot(hash, 16);
> +    hash ^= hash >> 16;
>      hash *= 0x85ebca6b;
> -    hash ^= hash_rot(hash, 13);
> +    hash ^= hash >> 13;
>      hash *= 0xc2b2ae35;
> -    hash ^= hash_rot(hash, 16);
> +    hash ^= hash >> 16;
>      return hash;
>  }
>
> --
> 1.7.2.5
>
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