Double-double Date #1533
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Double-double Date #1533
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Adapts Date to use a double-Double representation (the underlying representation is the sum of two double-precision values, giving about 106 bits of precision). Keeping a binary floating-point representation means that existing API that converts Date to/from Double values will not see a difference in behavior for simple cases (it will, however, become more accurate in some other cases). Every date computation that was previously exact is still exact. Many cases that previously might have rounded will now generate exact results. DateInterval gets the same treatment; both its start Date and duration are represented as double-Double quantities with this change. If we move forward with this change, we'll investigate adding new APIs to make it more convenient to specify high-precision Dates; this change merely makes it possible to do so.
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Converted to draft as I want to add some additional comments and tests before this moves forward, but the basic shape of the change is correct, I think. |
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@swift-ci test |
Previously these were disabled because of an API availability issue in 5.8/5.9; we're no longer developing for those targets, so let's re-enable these tests.
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Adapts Date to use a double-Double representation (the underlying representation is the sum of two double-precision values, giving about 106 bits of precision). Keeping a binary floating-point representation means that existing API that converts Date to/from Double values will not see a difference in behavior for simple cases (it will, however, become more accurate in some other cases). Every date computation that was previously exact is still exact. Many cases that previously might have rounded will now generate exact results.
DateInterval gets the same treatment; both its start Date and duration are represented as double-Double quantities with this change.
If we move forward with this change, we'll investigate adding new APIs to make it more convenient to specify high-precision Dates; this change merely makes it possible to do so.