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[stdlib] Align behavior of generic NaN conversion to that of concrete types #17746

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Merged
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Jul 5, 2018
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[stdlib] Align behavior of generic NaN conversion to that of concrete types #17746

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7 changes: 4 additions & 3 deletions stdlib/public/core/FloatingPoint.swift.gyb
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Original file line number Diff line number Diff line change
Expand Up @@ -2185,7 +2185,9 @@ extension BinaryFloatingPoint {
sign: source.sign,
exponentBitPattern: Self.nan.exponentBitPattern,
significandBitPattern: payload | Self.nan.significandBitPattern)
return payload_ == payload ? (value, true) : (value, false)
// We define exactness by equality after roundtripping; since NaN is never
// equal to itself, it can never be converted exactly.
return (value, false)
}

let exponent = source.exponent
Expand Down Expand Up @@ -2299,8 +2301,7 @@ extension BinaryFloatingPoint {
/// exactly.
///
/// If the given floating-point value cannot be represented exactly, the
/// result is `nil`. A value that is NaN ("not a number") cannot be
/// represented exactly if its payload cannot be encoded exactly.
/// result is `nil`.
///
/// - Parameter value: A floating-point value to be converted.
@inlinable // FIXME(sil-serialize-all)
Expand Down