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Correctly round Double(PseudoDecimal) #83

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Correctly round Double(PseudoDecimal) #83

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3 changes: 2 additions & 1 deletion Sources/RawStructuredFieldValues/PseudoDecimal.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -226,6 +226,7 @@ extension String {
// Swift Numerics would let us do this for all the floating point types.
extension Double {
public init(_ pseudoDecimal: PseudoDecimal) {
self = Double(pseudoDecimal.mantissa) * pow(10, Double(pseudoDecimal.exponent))
// Divide by an exact power of ten: multiplying by an inexact negative power of ten rounds twice.
self = Double(pseudoDecimal.mantissa) / pow(10, -Double(pseudoDecimal.exponent))
}
}
8 changes: 8 additions & 0 deletions Tests/StructuredFieldValuesTests/StructuredFieldDecoderTests.swift
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Expand Up @@ -182,6 +182,14 @@ final class StructuredFieldDecoderTests: XCTestCase {
XCTAssertEqual(ItemField(Double(5.0)), try StructuredFieldValueDecoder().decode(from: Array(headerField.utf8)))
}

func testDecodingDecimalAsDoubleIsCorrectlyRounded() throws {
XCTAssertEqual(ItemField(Double(0.3)), try StructuredFieldValueDecoder().decode(from: Array("0.3".utf8)))
XCTAssertEqual(
ItemField(Double(-19.993)),
try StructuredFieldValueDecoder().decode(from: Array("-19.993".utf8))
)
}

func testAskingForTheWrongType() throws {
let headerField = "gzip"
let intField = "5"
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