Re: [Boost-bugs] [Boost C++ Libraries] #11769: 64-bit hash_combine has weakness against zero input

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #11769: 64-bit hash_combine has weakness against zero input
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-10-28 13:27:38

#11769: 64-bit hash_combine has weakness against zero input
--------------------------------------+-------------------------
  Reporter:  andysem                  |      Owner:  danieljames
      Type:  Bugs                     |     Status:  new
 Milestone:  To Be Determined         |  Component:  hash
   Version:  Boost Development Trunk  |   Severity:  Problem
Resolution:                           |   Keywords:
--------------------------------------+-------------------------
Description changed by andysem:

Old description:

> The `hash_combine_impl` function for 64-bit `size_t` (see
> [https://github.com/boostorg/functional/blob/develop/include/boost/functional/hash/hash.hpp#L237

> here]) does not have an additive component. As a result, hashing strings
> of zeros always results in zero has value regardless of the length of the
> string.

New description:

 The `hash_combine_impl` function for 64-bit `size_t` (see
 [https://github.com/boostorg/functional/blob/develop/include/boost/functional/hash/hash.hpp#L237

 here]) does not have an additive component. As a result, hashing strings
 of zeros always results in zero hash value regardless of the length of the
 string.

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Ticket URL: <https://svn.boost.org/trac/boost/ticket/11769#comment:1>
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