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refactored to modernize and improve flow

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joaquintides
2023-05-18 20:18:58 +02:00
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doc/unordered/rationale.adoc
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= Implementation Rationale
== Closed-addressing containers
== Closed-addressing Containers
`boost::unordered_[multi]set` and `boost::unordered_[multi]map`
adhere to the standard requirements for unordered associative
@@ -74,7 +74,7 @@ Since release 1.80.0, prime numbers are chosen for the number of buckets in
tandem with sophisticated modulo arithmetic. This removes the need for "mixing"
the result of the user's hash function as was used for release 1.79.0.
== Open-addresing containers
== Open-addresing Containers
The C++ standard specification of unordered associative containers impose
severe limitations on permissible implementations, the most important being
@@ -86,7 +86,7 @@ The design of `boost::unordered_flat_set`/`unordered_node_set` and `boost::unord
guided by Peter Dimov's https://pdimov.github.io/articles/unordered_dev_plan.html[Development Plan for Boost.Unordered^].
We discuss here the most relevant principles.
=== Hash function
=== Hash Function
Given its rich functionality and cross-platform interoperability,
`boost::hash` remains the default hash function of open-addressing containers.
@@ -105,7 +105,7 @@ whereas in 32 bits _C_ = 0xE817FB2Du has been obtained from https://arxiv.org/ab
When using a hash function directly suitable for open addressing, post-mixing can be opted out by via a dedicated <<hash_traits_hash_is_avalanching,`hash_is_avalanching`>>trait.
`boost::hash` specializations for string types are marked as avalanching.
=== Platform interoperability
=== Platform Interoperability
The observable behavior of `boost::unordered_flat_set`/`unordered_node_set` and `boost::unordered_flat_map`/`unordered_node_map` is deterministically
identical across different compilers as long as their ``std::size_t``s are the same size and the user-provided
@@ -118,7 +118,7 @@ and https://en.wikipedia.org/wiki/ARM_architecture_family#Advanced_SIMD_(NEON)[N
this does not affect interoperatility. For instance, the behavior is the same
for Visual Studio on an x64-mode Intel CPU with SSE2 and for GCC on an IBM s390x without any supported SIMD technology.
== Concurrent Hashmap
== Concurrent Containers
The same data structure used by Boost.Unordered open-addressing containers has been chosen
also as the foundation of `boost::concurrent_flat_map`:
@@ -132,7 +132,7 @@ lookup that are lock-free up to the last step of actual element comparison.
of all elements between `boost::concurrent_flat_map` and `boost::unordered_flat_map`.
(This feature has not been implemented yet.)
=== Hash function and platform interoperability
=== Hash Function and Platform Interoperability
`boost::concurrent_flat_map` makes the same decisions and provides the same guarantees
as Boost.Unordered open-addressing containers with regards to