forked from boostorg/container_hash
Refactor links to no longer open up a new tab
This commit is contained in:
Christian Mazakas
@ -13,7 +13,7 @@
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* Support `std::string_view`, `std::error_code`, `std::error_condition`, `std::optional`, `std::variant`, `std::monostate` where available.
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* Update include paths from other Boost libraries.
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* Manually write out tuple overloads, rather than using the preprocessor to generate them. Should improve usability, due to better error messages, and easier debugging.
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* Fix tutorial example (https://svn.boost.org/trac/boost/ticket/11017[#11017^]).
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* Fix tutorial example (https://svn.boost.org/trac/boost/ticket/11017[#11017]).
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* Quick fix for hashing `vector<bool>` when using lib{cpp}. Will try to introduce a more general fix in the next release.
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== Boost 1.66.0
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@ -23,25 +23,25 @@
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* Support for `char16_t`, `char32_t`, `u16string`, `u32string`
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== Boost 1.64.0
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* Fix for recent versions of Visual {cpp} which have removed `std::unary_function` and `std::binary_function` (https://svn.boost.org/trac/boost/ticket/12353[#12353^]).
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* Fix for recent versions of Visual {cpp} which have removed `std::unary_function` and `std::binary_function` (https://svn.boost.org/trac/boost/ticket/12353[#12353]).
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== Boost 1.63.0
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* Fixed some warnings.
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* Only define hash for `std::wstring` when we know we have a `wchar_t`. Otherwise there's a compile error as there's no overload for hashing the characters in wide strings (https://svn.boost.org/trac/boost/ticket/8552[#8552^]).
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* Only define hash for `std::wstring` when we know we have a `wchar_t`. Otherwise there's a compile error as there's no overload for hashing the characters in wide strings (https://svn.boost.org/trac/boost/ticket/8552[#8552]).
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== Boost 1.58.0
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* Fixed strict aliasing violation (https://github.com/boostorg/container_hash/issues/3[GitHub #3^]).
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* Fixed strict aliasing violation (https://github.com/boostorg/container_hash/issues/3[GitHub #3]).
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== Boost 1.56.0
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* Removed some Visual {cpp} 6 workarounds.
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* Ongoing work on improving `hash_combine`. This changes the combine function which was previously defined in the reference documentation.
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== Boost 1.55.0
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* Simplify a SFINAE check so that it will hopefully work on Sun 5.9 (https://svn.boost.org/trac10/ticket/8822[#8822^]).
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* Suppress Visual {cpp} infinite loop warning (https://svn.boost.org/trac10/ticket/8568[#8568^]).
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* Simplify a SFINAE check so that it will hopefully work on Sun 5.9 (https://svn.boost.org/trac10/ticket/8822[#8822]).
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* Suppress Visual {cpp} infinite loop warning (https://svn.boost.org/trac10/ticket/8568[#8568]).
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== Boost 1.54.0
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* https://svn.boost.org/trac/boost/ticket/7957[Ticket 7957^]: Fixed a typo.
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* https://svn.boost.org/trac/boost/ticket/7957[Ticket 7957]: Fixed a typo.
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== Boost 1.53.0
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* Add support for `boost::int128_type` and `boost::uint128_type` where available - currently only `{int128}` and `unsigned {int128}` on some versions of gcc.
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@ -58,8 +58,8 @@
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* Updated to use the new config macros.
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== Boost 1.50.0
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* https://svn.boost.org/trac/boost/ticket/6771[Ticket 6771^]: Avoid gcc's `-Wfloat-equal` warning.
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* https://svn.boost.org/trac/boost/ticket/6806[Ticket 6806^]: Support `std::array` and `std::tuple` when available.
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* https://svn.boost.org/trac/boost/ticket/6771[Ticket 6771]: Avoid gcc's `-Wfloat-equal` warning.
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* https://svn.boost.org/trac/boost/ticket/6806[Ticket 6806]: Support `std::array` and `std::tuple` when available.
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* Add deprecation warning to the long deprecated `boost/container_hash/detail/container_fwd.hpp`.
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== Boost 1.46.0
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@ -69,8 +69,8 @@
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* Add option to prevent implicit conversions when calling `hash_value` by defining `BOOST_HASH_NO_IMPLICIT_CASTS`. When using `boost::hash` for a type that does not have `hash_value` declared but does have an implicit conversion to a type that does, it would use that implicit conversion to hash it. Which can sometimes go very wrong, e.g. using a conversion to `bool` and only hashing to 2 possible values. Since fixing this is a breaking change and was only approached quite late in the release cycle with little discussion it's opt-in for now. This, or something like it, will become the default in a future version.
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== Boost 1.43.0
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* https://svn.boost.org/trac/boost/ticket/3866[Ticket 3866^]: Don't foward declare containers when using gcc's parallel library, allow user to stop forward declaration by defining the `BOOST_DETAIL_NO_CONTAINER_FWD` macro.
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* https://svn.boost.org/trac/boost/ticket/4038[Ticket 4038^]: Avoid hashing `0.5` and `0` to the same number.
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* https://svn.boost.org/trac/boost/ticket/3866[Ticket 3866]: Don't foward declare containers when using gcc's parallel library, allow user to stop forward declaration by defining the `BOOST_DETAIL_NO_CONTAINER_FWD` macro.
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* https://svn.boost.org/trac/boost/ticket/4038[Ticket 4038]: Avoid hashing `0.5` and `0` to the same number.
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* Stop using deprecated `BOOST_HAS_*` macros.
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== Boost 1.42.0
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@ -84,15 +84,15 @@
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== Boost 1.39.0
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* Move the `hash_fwd.hpp` implementation into the hash subdirectory, leaving a forwarding header in the old location. You should still use the old location, the new location is mainly for implementation and possible modularization.
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* https://svn.boost.org/trac/boost/ticket/2412[Ticket 2412^]: Removed deprecated headers.
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* https://svn.boost.org/trac/boost/ticket/2957[Ticket 2957^]: Fix configuration for vxworks.
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* https://svn.boost.org/trac/boost/ticket/2412[Ticket 2412]: Removed deprecated headers.
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* https://svn.boost.org/trac/boost/ticket/2957[Ticket 2957]: Fix configuration for vxworks.
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== Boost 1.38.0
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* Changed the warnings in the deprecated headers from 1.34.0 to errors. These will be removed in a future version of Boost.
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* Moved detail headers out of `boost/container_hash/detail`, since they are part of `functional/hash`, not `container_hash`. `boost/container_hash/detail/container_fwd.hpp` has been moved to `boost/detail/container_fwd.hpp` as it's used outside of this library, the others have been moved to `boost/functional/hash/detail`.
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== Boost 1.37.0
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* http://svn.boost.org/trac/boost/ticket/2264[Ticket 2264^]: In Visual {cpp}, always use C99 float functions for long double and float as the {cpp} overloads aren't always availables.
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* http://svn.boost.org/trac/boost/ticket/2264[Ticket 2264]: In Visual {cpp}, always use C99 float functions for long double and float as the {cpp} overloads aren't always availables.
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== Boost 1.36.0
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* Stop using OpenBSD's dodgy `std::numeric_limits`.
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@ -102,20 +102,20 @@
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== Boost 1.35.0
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* Support for `long long`, `std::complex`.
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* Improved algorithm for hashing floating point numbers:
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** Improved portablity, as described by Daniel Krügler in http://lists.boost.org/boost-users/2005/08/13418.php[a post to the boost users list^].
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** Improved portablity, as described by Daniel Krügler in http://lists.boost.org/boost-users/2005/08/13418.php[a post to the boost users list].
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** Fits more information into each combine loop, which can reduce the the number of times combine is called and hopefully give a better quality hash function.
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** Improved the algorithm for hashing floating point numbers.
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** On Cygwin use a binary hash function for floating point numbers, as Cygwin doesn't have decent floating point functions for `long double`.
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** Never uses `fpclass` which doesn't support `long double`.
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** http://svn.boost.org/trac/boost/ticket/1064[Ticket 1064^]: Removed unnecessary use of errno.
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** http://svn.boost.org/trac/boost/ticket/1064[Ticket 1064]: Removed unnecessary use of errno.
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* Explicitly overload for more built in types.
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* Minor improvements to the documentation.
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* A few bug and warning fixes:
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** http://svn.boost.org/trac/boost/ticket/1509[Ticket 1509^]: Suppress another Visual {cpp} warning.
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** http://svn.boost.org/trac/boost/ticket/1509[Ticket 1509]: Suppress another Visual {cpp} warning.
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** Some workarounds for the Sun compilers.
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== Boost 1.34.1
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* https://svn.boost.org/trac10/ticket/952[Ticket 952^]: Suppress incorrect 64-bit warning on Visual {cpp}.
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* https://svn.boost.org/trac10/ticket/952[Ticket 952]: Suppress incorrect 64-bit warning on Visual {cpp}.
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== Boost 1.34.0
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* Use declarations for standard classes, so that the library doesn't need to include all of their headers
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@ -45,7 +45,7 @@ class point
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Calls to `hash_combine` incrementally build the hash from the different members of `point`, it can be repeatedly called for any number of elements. It calls `hash_value` on the supplied element, and combines it with the seed.
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Full code for this example is at link:../../examples/point.cpp[/libs/container_hash/examples/point.cpp^].
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Full code for this example is at link:../../examples/point.cpp[/libs/container_hash/examples/point.cpp].
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[NOTE]
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====
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@ -77,4 +77,4 @@ std::vector<std::string> some_strings;
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std::size_t hash = boost::hash_range(some_strings.begin(), some_strings.end());
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----
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Note that when writing template classes, you might not want to include the main hash header as it's quite an expensive include that brings in a lot of other headers, so instead you can include the `<boost/container_hash/hash_fwd.hpp>` header which forward declares `boost::hash`, `boost::hash_range` and `boost::hash_combine`. You'll need to include the main header before instantiating `boost::hash`. When using a container that uses `boost::hash` it should do that for you, so your type will work fine with the boost hash containers. There's an example of this in link:../../examples/template.hpp[template.hpp^] and link:../../examples/template.cpp[template.cpp^].
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Note that when writing template classes, you might not want to include the main hash header as it's quite an expensive include that brings in a lot of other headers, so instead you can include the `<boost/container_hash/hash_fwd.hpp>` header which forward declares `boost::hash`, `boost::hash_range` and `boost::hash_combine`. You'll need to include the main header before instantiating `boost::hash`. When using a container that uses `boost::hash` it should do that for you, so your type will work fine with the boost hash containers. There's an example of this in link:../../examples/template.hpp[template.hpp] and link:../../examples/template.cpp[template.cpp].
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@ -63,6 +63,6 @@ assert(books.find(knife) != books.end());
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assert(books.find(dandelion) == books.end());
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----
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The full example can be found in: link:../../examples/books.hpp[/libs/container_hash/examples/books.hpp^] and link:../../examples/books.cpp[/libs/container_hash/examples/books.cpp^].
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The full example can be found in: link:../../examples/books.hpp[/libs/container_hash/examples/books.hpp] and link:../../examples/books.cpp[/libs/container_hash/examples/books.cpp].
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TIP: When writing a hash function, first look at how the equality function works. Objects that are equal must generate the same hash value. When objects are not equal they should generate different hash values. In this object equality was based just on the id so the hash function only hashes the id. If it was based on the object's name and author then the hash function should take them into account (how to do this is discussed in the next section).
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@ -3,16 +3,16 @@
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:idprefix: intro_
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`boost::hash` is an implementation of the https://en.wikipedia.org/wiki/Hash_function[hash function^] object specified by the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf[Draft Technical Report on C++ Library Extensions^] (TR1). It is the default hash function for link:../../../unordered/index.html[Boost.Unordered^], link:../../../intrusive/index.html[Boost.Intrusive^]'s unordered associative containers, and link:../../../multi_index/index.html[Boost.MultiIndex^]'s hash indicies and link:../../../bimap/index.html[Boost.Bimap^]'s `unordered_set_of`.
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`boost::hash` is an implementation of the https://en.wikipedia.org/wiki/Hash_function[hash function] object specified by the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf[Draft Technical Report on C++ Library Extensions] (TR1). It is the default hash function for link:../../../unordered/index.html[Boost.Unordered], link:../../../intrusive/index.html[Boost.Intrusive]'s unordered associative containers, and link:../../../multi_index/index.html[Boost.MultiIndex]'s hash indicies and link:../../../bimap/index.html[Boost.Bimap]'s `unordered_set_of`.
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As it is compliant with http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf[TR1^], it will work with:
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As it is compliant with http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf[TR1], it will work with:
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* integers
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* floats
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* pointers
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* strings
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It also implements the extension proposed by Peter Dimov in issue 6.18 of the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1837.pdf[Library Extension Technical Report Issues List^] (page 63), this adds support for:
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It also implements the extension proposed by Peter Dimov in issue 6.18 of the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1837.pdf[Library Extension Technical Report Issues List] (page 63), this adds support for:
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* arrays
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* `std::pair`
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@ -79,4 +79,4 @@ namespace foo
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}
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----
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Full code for this example is at link:../../examples/portable.cpp[/libs/container_hash/examples/portable.cpp^].
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Full code for this example is at link:../../examples/portable.cpp[/libs/container_hash/examples/portable.cpp].
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@ -3,7 +3,7 @@
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:idprefix: rationale_
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The rationale can be found in the original designfootnote:[issue 6.18 of the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1837.pdf[Library Extension Technical Report Issues List^] (page 63)].
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The rationale can be found in the original designfootnote:[issue 6.18 of the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1837.pdf[Library Extension Technical Report Issues List] (page 63)].
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== Quality of the hash function
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@ -11,6 +11,6 @@ Many hash functions strive to have little correlation between the input and outp
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But the standard has no such requirement for the hash function, it just requires that the hashes of two different values are unlikely to collide. Containers or algorithms designed to work with the standard hash function will have to be implemented to work well when the hash function's output is correlated to its input. Since they are paying that cost a higher quality hash function would be wasteful.
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For other use cases, if you do need a higher quality hash function, then neither the standard hash function or `boost::hash` are appropriate. There are several options available. One is to use a second hash on the output of this hash function, such as http://web.archive.org/web/20121102023700/http://www.concentric.net/~Ttwang/tech/inthash.htm[Thomas Wang's hash function^]. This this may not work as well as a hash algorithm tailored for the input.
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For other use cases, if you do need a higher quality hash function, then neither the standard hash function or `boost::hash` are appropriate. There are several options available. One is to use a second hash on the output of this hash function, such as http://web.archive.org/web/20121102023700/http://www.concentric.net/~Ttwang/tech/inthash.htm[Thomas Wang's hash function]. This this may not work as well as a hash algorithm tailored for the input.
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For strings there are several fast, high quality hash functions available (for example http://code.google.com/p/smhasher/[MurmurHash3^] and http://code.google.com/p/cityhash/[Google's CityHash^]), although they tend to be more machine specific. These may also be appropriate for hashing a binary representation of your data - providing that all equal values have an equal representation, which is not always the case (e.g. for floating point values).
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For strings there are several fast, high quality hash functions available (for example http://code.google.com/p/smhasher/[MurmurHash3] and http://code.google.com/p/cityhash/[Google's CityHash]), although they tend to be more machine specific. These may also be appropriate for hashing a binary representation of your data - providing that all equal values have an equal representation, which is not always the case (e.g. for floating point values).
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@ -3,7 +3,7 @@
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:idprefix: ref_
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For the full specification, see section 6.3 of the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf[C++ Standard Library Technical Report^] and issue 6.18 of the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1837.pdf[Library Extension Technical Report Issues List^] (page 63).
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For the full specification, see section 6.3 of the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf[C++ Standard Library Technical Report] and issue 6.18 of the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1837.pdf[Library Extension Technical Report Issues List] (page 63).
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== Header <boost/container_hash/hash.hpp>
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@ -121,7 +121,7 @@ namespace boost {
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=== hash
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`boost::hash` — A http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf[TR1^] compliant hash function object.
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`boost::hash` — A http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf[TR1] compliant hash function object.
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==== Synopsis
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@ -3,7 +3,7 @@
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:idprefix: tutorial_
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When using a hash index with link:../../../multi_index/index.html[Boost.MultiIndex^], you don't need to do anything to use `boost::hash` as it uses it by default. To find out how to use a user-defined type, read the <<custom,section on extending boost::hash for a custom data type>>.
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When using a hash index with link:../../../multi_index/index.html[Boost.MultiIndex], you don't need to do anything to use `boost::hash` as it uses it by default. To find out how to use a user-defined type, read the <<custom,section on extending boost::hash for a custom data type>>.
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If your standard library supplies its own implementation of the unordered associative containers and you wish to use `boost::hash`, just use an extra template parameter:
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Block a user