[compiler-rt] r212704 - [msan] Switch chained origins hash to murmur2.

[David Blaikie]

On Thu, Jul 10, 2014 at 4:02 AM, Evgeniy Stepanov
<eugeni.stepanov at gmail.com> wrote:
> Author: eugenis
> Date: Thu Jul 10 06:02:33 2014
> New Revision: 212704
>
> URL: http://llvm.org/viewvc/llvm-project?rev=212704&view=rev
> Log:
> [msan] Switch chained origins hash to murmur2.

Should we document that it's murmur2 in a comment and/or put it in
some reusable function?

>
> Modified:
>     compiler-rt/trunk/lib/msan/msan_chained_origin_depot.cc
>
> Modified: compiler-rt/trunk/lib/msan/msan_chained_origin_depot.cc
> URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/msan/msan_chained_origin_depot.cc?rev=212704&r1=212703&r2=212704&view=diff
> ==============================================================================
> --- compiler-rt/trunk/lib/msan/msan_chained_origin_depot.cc (original)
> +++ compiler-rt/trunk/lib/msan/msan_chained_origin_depot.cc Thu Jul 10 06:02:33 2014
> @@ -19,7 +19,30 @@ namespace __msan {
>  struct ChainedOriginDepotDesc {
>    u32 here_id;
>    u32 prev_id;
> -  u32 hash() const { return (here_id * 0x1f1f1f1f) ^ prev_id; }
> +  u32 hash() const {
> +    const u32 m = 0x5bd1e995;
> +    const u32 seed = 0x9747b28c;
> +    const u32 r = 24;
> +    u32 h = seed;
> +    u32 k = here_id;
> +    k *= m;
> +    k ^= k >> r;
> +    k *= m;
> +    h *= m;
> +    h ^= k;
> +
> +    k = prev_id;
> +    k *= m;
> +    k ^= k >> r;
> +    k *= m;
> +    h *= m;
> +    h ^= k;
> +
> +    h ^= h >> 13;
> +    h *= m;
> +    h ^= h >> 15;
> +    return h;
> +  }
>    bool is_valid() { return true; }
>  };
>
>
>
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