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Update documentation

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Peter Dimov
2023-04-05 17:34:08 +03:00
parent ad89c02360
commit e62a268566
2 changed files with 30 additions and 3 deletions
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16
doc/hash/notes.adoc
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@@ -55,6 +55,22 @@ to be templates constrained on e.g. `std::is_integral` or its moral
equivalent. This causes types convertible to an integral to no longer equivalent. This causes types convertible to an integral to no longer
match, avoiding the problem. match, avoiding the problem.
== Hash Value Stability
In general, the library does not promise that the hash values will stay
the same from release to release (otherwise improvements would be
impossible). However, historically values have been quite stable. Before
release 1.81, the previous changes have been in 1.56 (a better
`hash_combine`) and 1.78 (macOS-specific change to `hash_combine`.)
Code should generally not depend on specific hash values, but for those
willing to take the risk of occasional breaks due to hash value changes,
the library now has a test that checks hash values for a number of types
against reference values (`test/hash_reference_values.cpp`),
whose https://github.com/boostorg/container_hash/commits/develop/test/hash_reference_values.cpp[version history]
can be used as a rough guide to when hash values have changed, and for what
types.
== hash_combine == hash_combine
The initial implementation of the library was based on Issue 6.18 of the The initial implementation of the library was based on Issue 6.18 of the

17
doc/hash/recent.adoc
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@@ -14,8 +14,10 @@ https://www.boost.org/LICENSE_1_0.txt
* Added `is_tuple_like` and an overload of `hash_value` for * Added `is_tuple_like` and an overload of `hash_value` for
tuple-like types. tuple-like types.
* Changed string hashing to use * Changed string hashing to use
https://github.com/pdimov/mulxp_hash[`mulxp1_hash`]. This https://github.com/pdimov/mulxp_hash[`mulxp1_hash`],
improves both quality and speed. improving both quality and speed. This changes the hash values
for string-like types (ranges of `char`, `signed char`,
`unsigned char`, `std::byte`, `char8_t`).
== Boost 1.81.0 == Boost 1.81.0
@@ -33,9 +35,18 @@ Major update.
* Described structs and classes (those annotated with * Described structs and classes (those annotated with
`BOOST_DESCRIBE_STRUCT` or `BOOST_DESCRIBE_CLASS`) are now `BOOST_DESCRIBE_STRUCT` or `BOOST_DESCRIBE_CLASS`) are now
supported out of the box. supported out of the box.
* `hash_combine` has been improved. * `hash_combine` has been improved. This changes the hash values
of composite (container and tuple) types and of scalar types
bigger than `size_t`.
* The performance (and quality, as a result of the above change) * The performance (and quality, as a result of the above change)
of string hashing has been improved. `boost::hash` for strings of string hashing has been improved. `boost::hash` for strings
now passes SMHasher in 64 bit mode. now passes SMHasher in 64 bit mode.
* The documentation has been substantially revised to reflect * The documentation has been substantially revised to reflect
the changes. the changes.
== Boost 1.78.0
* Fixed `hash_combine` so that its behavior no longer depends
on whether `size_t` is the exact same type as `boost::uint64_t`
(which wasn't the case on macOS). This changes the hash values
of composite (container and tuple) types on macOS.