Improve [U]Int128 string conversion performance. #65508
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stephentyrone
requested changes
Jun 12, 2023
stdlib/public/core/Int128.swift.gyb
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| private static func times<T:FixedWidthInteger>( | ||
| x: T, timesRadix radix: UInt64, toPower n: Int) -> T { | ||
| // calculate the powers of the radix and store in a table | ||
| if powers.isEmpty || powers.first! != radix { |
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This has an obvious toctou race condition, as well as a more subtle race condition on targets without total store ordering. I don't think that it's actually possible to use a lazily computed table of powers like this without an explicit lock. Given what the expected distribution of radices looks like, simply covering power-of-two bases with a precomputed table for base 10 would be a much more attractive solution.
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Thanks for the feedback! Will do a precomputed table for base 10 and powers of 2.
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@stephentyrone, latest update should fix this race condition issue.
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String to [U]Int128 conversions are 9 times faster.
[U]Int128 to String conversions are 25 times faster.
@stephentyrone suggested my [U]Int128 changes would be better placed in the standard library.
[U]Int128 probably fits better in the standard library itself (there's already a partial implementation there to support Duration.