Introduce til::presorted_static_map #7640
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til::static_map can't be constexpr until we move to C++20. It can't be constexpr because std::sort isn't constexpr until then. This poses a problem: if we start using it and treating it like a map, we'll incur a potentially high cost in static initialization in both code size in .text and runtime. This commit introduces presorted_static_map, which is static_map except that it doesn't automatically sort its keys. That's the only difference. At this point, it's just a maplike interface to a constant array of pairs that does a binary search. It should be used for small tables that are used infrequently enough as to not warrant their cost in code size or initialization time. It should also be used for tables that aren't going to be edited much by developers (like the color table in #7578.)
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Gotta say it’s a bit weird to ask people to “presort” things in source code. But here we are. The road of test drive for static_map is a lot bumpier than I anticipated... |
| static constexpr til::presorted_static_map intIntMap{ | ||
| std::pair{ 1, 100 }, | ||
| std::pair{ 3, 300 }, | ||
| std::pair{ 5, 500 }, | ||
| }; |
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So, what happens for the following two scenarios:
// 1. sorted, but backwards
static constexpr til::presorted_static_map intIntMap{
std::pair{ 5, 500 },
std::pair{ 3, 300 },
std::pair{ 1, 100 },
};
// 2. not sorted, but declared as presorted
static constexpr til::presorted_static_map intIntMap{
std::pair{ 3, 300 },
std::pair{ 1, 100 },
std::pair{ 5, 500 },
};
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Read the comment in the header!
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// A failure to sort your keys will result in unusual
// runtime behavior, but no error messages will be
// generated.
ah...and I'm guessing reverse doesn't count :(
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Kinda wish it were possible to throw a compiler error if they weren't sorted...
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Alas! That might require constexpr sort!
Unless i can do constexpr “check if the predicate is false” for every element pair ??
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yeah there might be no good option here. I'm gonna sign it because it is probably worth the risk to hold us over until the real goodness arrives.
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For reference, I checked today and |
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merged commit * Run all images through ImgBot (CC-8169) * Fix potential over/underflow as noted by "TODO:" comment (CC-8081) * Fix garbling when copying multibyte text via OSC 52 (CC-7870) * UIA: throw E_FAIL for out-of-bounds text (CC-8052) * Consider the GlyphWidth when calculate the postion of matched word in URL detecting (CC-8124) * Make the link underline less obtrusive; don't use it for pattern (GH-8148) * Fully regenerate CodepointWidthDetector from Unicode 13.0 (GH-8035) * Prepare for the primary branch name to change to main (GH-7985) * Hash the URI as part of the hyperlink ID (GH-7940) * Introduce til::presorted_static_map (GH-7640) * Prevent leftover cursor fragments when scrolling in PowerShell (CC-8173) * Add support for the DECREQTPARM report (CC-7939) * Refactor VT parameter handling (CC-7799) * Add support for the "blink" graphic rendition attribute (CC-7490) * Combine the parsing & dispatch blocks for OSC actions (CC-8202) * Add support for autodetecting URLs and making hyperlinks (CC-7691) * Copy _currentHyperlinkId when copying the buffer (CC-8074) * Fix the "visual representation" optimization for hyperlinks (CC-7738) * Optimize the binary size of the XOrg color table (CC-7929) * Add support for more OSC color formats (CC-7578) Related work items: MSFT-30259074
til::static_map can't be constexpr until we move to C++20.
It can't be constexpr because std::sort isn't constexpr until then.
This poses a problem: if we start using it and treating it like a map,
we'll incur a potentially high cost in static initialization in both
code size in .text and runtime.
This commit introduces presorted_static_map, which is static_map except
that it doesn't automatically sort its keys. That's the only difference.
At this point, it's just a maplike interface to a constant array of
pairs that does a binary search. It should be used for small tables that
are used infrequently enough as to not warrant their cost in code size
or initialization time. It should also be used for tables that aren't
going to be edited much by developers (like the color table in #7578.)