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Niels Lohmann
5b08041308
ordered_map keeps its elements in a vector and searches it linearly for every key it adds, so parsing an object with n keys into ordered_json took O(n^2) key comparisons: 33 billion instructions for one object with 30 000 keys, where json needs 245 million. From 64 keys on, the DOM parser now keeps a hash table of the keys of the open object (hashes and positions only; the elements stay in the vector) and finds duplicate keys there. The result is the same, including the position of a key that occurs twice. Smaller objects, std::map based objects and key types without std::hash are untouched. ordered_json parse, macOS instructions: object with 1 000 keys 64.8 M -> 14.6 M, 10 000 keys 5 104 M -> 38.7 M, 30 000 keys 33 358 M -> 89 M. Linux Ir of an object with 2 000 keys: 43.0 M -> 1.9 M (GCC), 37.9 M -> 1.8 M (Clang). Signed-off-by: Niels Lohmann <mail@nlohmann.me>