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Use Schubfach algorithm for float repr - #2128
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🟡 Changes recommended
The upstream MIT notice is missing from the ports and binary packages, and the non-NET formatting implementations lack independent boundary-value coverage.
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What changed in this PR
Replaces float representation formatting with a Schubfach implementation to produce shortest round-tripping strings across supported runtimes, addressing the excess digits reported in #1626.
Changes:
- Adds the converter and a source generator for its power-of-ten lookup table.
- Routes float representations through Schubfach and reports
"short"representation style on all targets. - Updates formatting, array and pickle expectations, and enables additional float tests on .NET Core.
| File | Description |
|---|---|
| tests/suite/test_formatting.py | Removes legacy float representation expected failures. |
| tests/suite/stdlib/test_float.py | Enables two float tests on .NET Core. |
| tests/suite/modules/type_related/test_array.py | Uses shortest float representations in array expectations. |
| tests/suite/modules/io_related/test_cPickle.py | Updates selection of legacy pickle expectations. |
| src/roslyn/IronPython.SourceGenerator/SchubfachGenerator.cs | Generates power-of-ten significands. |
| src/roslyn/IronPython.SourceGenerator/IronPython.SourceGenerator.csproj | Defines the source-generator project. |
| src/roslyn/IronPython.Analyzer/IronPython.Analyzer.csproj | Marks the analyzer as a Roslyn component. |
| src/core/IronPython/Runtime/Schubfach.cs | Implements conversion and Python-style formatting. |
| src/core/IronPython/Runtime/Operations/FloatOps.cs | Delegates float representation to Schubfach. |
| src/core/IronPython/Modules/sys.cs | Reports short float representation style universally. |
| src/core/IronPython/IronPython.csproj | References the source generator as an analyzer. |
| IronPython.slnx | Adds the source-generator project to the solution. |
Review effort: Balanced
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| // Copyright (c) 2025 Victor Zverovich | ||
| // Distributed under the MIT license. | ||
| // Ported from schubfach.cc of https://github.com/vitaut/schubfach. |
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Licensing is a general issue which probably warrants its own PR...
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Testing Copilot… 😃 |
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Use the Schubfach algorithm for float repr, ported from https://github.com/vitaut/schubfach. This now gives the shortest round-tripping string, matching CPython. I opted to use this across the board (including for .NET since it's faster and .NET 10 has a bug with its "R" formatting).
Resolves #1626