[Boost-bugs] [Boost C++ Libraries] #12171: boost::multiprecision should provide a hash function

Subject: [Boost-bugs] [Boost C++ Libraries] #12171: boost::multiprecision should provide a hash function
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2016-05-02 09:46:39

#12171: boost::multiprecision should provide a hash function
-------------------------------------------------+-------------------------
 Reporter:  Tassilo Glander <tassilo.glander@…>  |      Owner:  johnmaddock
     Type:  Feature Requests                     |     Status:  new
Milestone:  To Be Determined                     |  Component:
  Version:  Boost 1.60.0                         |  multiprecision
 Keywords:                                       |   Severity:
                                                 |  Optimization
-------------------------------------------------+-------------------------
 For boost::multiprecision types to be used in std::unordered_map etc.,
 they need to provide a hash function. A straightforward way on cpp_int
 would be to use the internal limbs like:

 size_t getHashCode() const
 {
     std::size_t result = _number.sign();
     std::size_t size = _number.backend().size();
     auto p = _number.backend().limbs();

     for (std::size_t i = 0; i < size; ++i) {
         boost::hash_combine(result, *p);
         ++p;
     }
     return result;
 }
 and the accompanying hash functor.

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Ticket URL: <https://svn.boost.org/trac/boost/ticket/12171>
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