this post was submitted on 28 Aug 2023
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The Little Things: The Missing Performance in std::vector (codingnest.com)
submitted 1 year ago by MarekKnapek@programming.dev to c/programming@programming.dev
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[–] kornel@programming.dev 6 points 1 year ago* (last edited 1 year ago) (1 children)

I don't know about C++, but in Rust the push is inline, and still doesn't always optimize checks away due to an annoying edge case: integer overflow. Reserving (old_len + new_len) could give you a smaller buffer than new_len. The optimizer sees it and is pedantic about it.

[–] robinm@programming.dev 1 points 1 year ago (1 children)

In C++ integer overflow is UB so this edge case cannot exist

[–] kornel@programming.dev 3 points 1 year ago (1 children)

Only signed overflow. size_t is unsigned.

[–] robinm@programming.dev 1 points 1 year ago* (last edited 1 year ago)

That's totally right but I thought you were talking about signed numbers since you said “integer overflow”. I forgot that len is usually unsigned in C++.