Don't use input.count in PrefixThrough and PrefixUpTo for speedup. #354
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Calling Substring.count will calculate the length of the string the first time it is called which for large strings can be slow.
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The CI Ubuntu test failure is the same error I get for both the benchmark and tests with Swift 6. |
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I have made a simple HTML tokenizer and noticed using Instruments that
PrefixThroughwas spending a lot of time inSubstring.count, which in turn was callingdistance(from:to:). I assume this is because the character count of a substring isn't known until calculated due to how Unicode works. This patch replaces the substring count check with a match end index check instead.I was unable to make sense of the results from the benchmark app, but in my HTML project (link provided) there was a substantial speedup. In that repo there is a benchmark app in the branch
swift-parsing, and you can switch between swift-parsing versions inPackage.swift.https://github.com/BjornRuud/HTMLLexer.git