WebThe std::unordered_map is a chaining hash table which means that for each pair of 16-bit values it needs to store a 64-bit pointer, this creates an especially large overhead in this case. I ended up sorting the values first and then computing the histograms from the sorted arrays, which takes much longer, but uses the minimum amount of memory. WebThis defaults to hash, which returns a hash value with a probability of collision approaching 1.0/std::numeric_limits::max(). The unordered_map object uses the hash values returned by this function to organize its elements internally, speeding up the process of locating individual elements. Aliased as member type unordered_map::hasher.
Boost.MultiIndex Documentation - Tutorial - Index types - 1.82.0
WebNov 20, 2013 · 1 Answer Sorted by: 4 The primary use of the std::hash function is the object used to obtain a hash value from a key in the std::unordered_* group of containers. These will always contain and use a corresponding object, possibly, using the empty base optimization to avoid it taking any memory. WebThe creator claims that it uses less memory than Google's dense_hash_map but has similiar performance. But as you can see from other posts here new hash map implementations pop up quite continously. According to a post I read hopscotch is supposed to be faster than the ska::flat_hash_map. Either way it is a lot faster than the maps in std. different word for heavily
Custom C++20 Memory Allocators for STL Containers
WebApr 30, 2024 · Hash function The default hash function used by the structure depends on the presence of std::string_view. If it is available, std::hash is used, otherwise a simple FNV-1a hash function is used to avoid any dependency. In addition to the above, the standard library provides specializations for all (scoped and unscoped) enumeration types. These may be (but are not required to be) implemented as std::hash::type>. The standard library provides enabled specializations of std::hash for std::nullptr_tand … See more The actual hash functions are implementation-dependent and are not required to fulfill any other quality criteria except those specified above. Notably, some … See more Note: additional specializations for std::pair and the standard container types, as well as utility functions to compose hashes are available in boost::hash. See more The following behavior-changing defect reports were applied retroactively to previously published C++ standards. See more WebApr 25, 2024 · Two common strategies for hash table memory layouts are indirect (typically with a pointer stored in the main array) and direct (with the memory of the keys and values incorporated directly into the main hash array). Direct storage algorithms must use probing for conflict resolution unless they store additional metadata. different word for heads up