Boost Unordered Translation (zh_Hans)/Doc / Modules / Root / Pages / Hash Quality (adoc)

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8 :45

	English By setting the `link:../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]` trait, we inform Boost.Unordered that `my_string_hash_function` is of sufficient quality to be used directly without any post-mixing safety net. This comes at the risk of degraded performance in the cases where the hash function is not as well-behaved as we've declared. 387/10000 · 387
9 :52

	English Container Statistics 20/10000 · 20
10 :54

	English If we globally define the macro `BOOST_UNORDERED_ENABLE_STATS`, open-addressing and concurrent containers will calculate some internal statistics directly correlated to the quality of the hash function: 202/10000 · 202
11 :75

	English The `stats` object provides the following information: 54/10000 · 54
12 :108

	English Statistics for three internal operations are maintained: insertions (without considering the previous lookup to determine that the key is not present yet), successful lookups, and unsuccessful lookups (including those issued internally when inserting elements). _Probe length_ is the number of xref:structures.adoc#structures_open_addressing_containers[bucket groups] accessed per operation. If the hash function behaves properly: 431/10000 · 431
13 :115

	English Average probe lengths should be close to 1.0. 45/10000 · 45
14 :116

	English The average number of comparisons per successful lookup should be close to 1.0 (that is, 88/10000 · 88
15 :117

	English just the element found is checked). 35/10000 · 35
16 :118

	English The average number of comparisons per unsuccessful lookup should be close to 0.0. 81/10000 · 81
17 :120

	English An link:../../../benchmark/string_stats.cpp[example^] is provided that displays container statistics for `boost::hash<std::string>`, an implementation of the https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function#FNV-1a_hash[FNV-1a hash^] and two ill-behaved custom hash functions that have been incorrectly marked as avalanching: 350/10000 · 350
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