Reimplement Floating-Point Parsing in pure Swift #85797
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tbkka
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@swift-ci Please test |
tbkka
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Dec 2, 2025
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| #if !((os(macOS) || targetEnvironment(macCatalyst)) && arch(x86_64)) | ||
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| @available(SwiftStdlib 5.3, *) |
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@stephentyrone Any thoughts on whether I can delete this entire function? Since it was public before, it's conceivable that someone was calling it directly, but no stdlib code ever called it.
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@swift-ci Please test |
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@swift-ci Please test |
3 similar comments
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@swift-ci Please test |
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@swift-ci Please test |
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@swift-ci Please test |
glessard
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Dec 4, 2025
| // Caveat: _swift_stdlib_strto{f,d,ld}_clocale() was called directly from inlineable | ||
| // code until Feb 2020 (commit 4d0e2adbef4d changed this), so they need to be | ||
| // exported with the same C-callable ABI for as long as we support code compiled | ||
| // with Swift 5.3. |
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Do we have a test calling the compatibility symbols directly, to avoid inattention-induced rot?
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We have the ABI checks to verify the symbols are still present, but you're right that it would be good to have something stronger.
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@swift-ci Please test macOS |
This reimplements the underlying support for `Float16(_:StringSlice)`, `Float32(_:StringSlice)`, and `Float64(_:StringSlice)` in pure Swift, using the same core algorithm currently used by Apple's libc. Those `StringSlice` initializers are in turn used by `Float16(_:String)`, `Float32(_:String)`, and `Float64(_:String)`. **Supports Embedded**: This fully supports Embedded Swift and insulates us from variations in libc implementations. **Corrects bugs in Float16 parsing**: The previous version of `Float16` parsing called libc `strtof()` to parse to a 32-bit float, then rounded to `Float16`. (This was necessary because float16 parsing functions are not widely supported in C implementations.) This double-rounding systematically corrupted NaN payloads and resulted in 1 ULP errors for certain decimal and hexadecimal inputs. The new version parses `Float16` directly, avoiding these errors. **Modest perforamnce improvement**: The old version had to copy the Swift string to construct a C string. For inputs longer than 15 characters, this typically required a heap allocation, which added up to 20% to the runtime. The new version parses directly from a Swift string, avoiding this copy and heap allocation.
Because these support functions used to be implemented in C, they could be present on macOS x86_64, even though Float16 isn't supported there otherwise. With the new Swift implementation, we can't define these functions on x86_64 macOS, so remove them from the expected list.
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This reimplements the underlying support for
Float16(_:Substring),Float32(_:Substring), andFloat64(_:Substring)in pure Swift, using the same fast algorithms currently used by Apple's libc. ThoseSubstringinitializers are in turn used byFloat16(_:String),Float32(_:String), andFloat64(_:String).Supports Embedded: This fully supports both Embedded and non-Embedded Swift and insulates us from variations in libc implementations.
Corrects bugs in Float16 parsing: The previous version of
Float16parsing called libcstrtof()to parse to a 32-bit float, then rounded toFloat16. (This was necessary because float16 parsing functions are not widely supported in C implementations.) This double-rounding systematically corrupted NaN payloads and resulted in 1 ULP errors for certain decimal and hexadecimal inputs. The new version parsesFloat16directly, avoiding these errors.Modest performance improvement: The old version had to copy the Swift string to construct a C string. This often incurred a heap allocation, which added up to 20% to the runtime. The new version parses directly from a Swift string, avoiding this copy and heap allocation.