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SR-13015: Decimal calculation incorrect on Linux #2827

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Merged
merged 1 commit into from
Jun 21, 2020
Merged

SR-13015: Decimal calculation incorrect on Linux #2827

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2 changes: 1 addition & 1 deletion Sources/Foundation/Decimal.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -1025,7 +1025,7 @@ fileprivate func integerMultiply<T:VariableLengthNumber>(_ big: inout T,
accumulator = UInt32(carry) + bigij + UInt32(right[j]) * UInt32(left[i])
carry = UInt16(truncatingIfNeeded:accumulator >> 16)
big[i+j] = UInt16(truncatingIfNeeded:accumulator)
} else if carry != 0 || (right[j] == 0 && left[j] == 0) {
} else if carry != 0 || (right[j] > 0 && left[i] > 0) {
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This will overflow if the accumulator above would be non-zero, ie if there's a carry or both right and left elements that are multiplied are non-zero.

return .overflow
}
}
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51 changes: 49 additions & 2 deletions Tests/Foundation/Tests/TestDecimal.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -342,7 +342,7 @@ class TestDecimal: XCTestCase {
XCTAssertEqual(otherBits + Decimal(1), highBit)
}

func test_Misc() {
func test_Misc() throws {
XCTAssertEqual(.minus, Decimal(-5.2).sign)
XCTAssertEqual(.plus, Decimal(5.2).sign)
var d = Decimal(5.2)
Expand Down Expand Up @@ -426,6 +426,23 @@ class TestDecimal: XCTestCase {
XCTAssertEqual(expected, pow(power, j))
}
}

do {
// SR-13015
let a = try XCTUnwrap(Decimal(string: "119.993"))
let b = try XCTUnwrap(Decimal(string: "4.1565"))
let c = try XCTUnwrap(Decimal(string: "18.209"))
let d = try XCTUnwrap(Decimal(string: "258.469"))
let ab = a * b
let aDivD = a / d
let caDivD = c * aDivD
XCTAssertEqual(ab, try XCTUnwrap(Decimal(string: "498.7509045")))
XCTAssertEqual(aDivD, try XCTUnwrap(Decimal(string: "0.46424522863476857959755328492004843907")))
XCTAssertEqual(caDivD, try XCTUnwrap(Decimal(string: "8.453441368210501065891847765109162027")))

let result = (a * b) + (c * (a / d))
XCTAssertEqual(result, try XCTUnwrap(Decimal(string: "507.2043458682105010658918477651091")))
}
}

func test_MultiplicationOverflow() {
Expand Down Expand Up @@ -522,7 +539,7 @@ class TestDecimal: XCTestCase {
XCTAssertEqual(0, result._isNegative, "0 * -1")
}

func test_Normalise() {
func test_Normalise() throws {
var one = Decimal(1)
var ten = Decimal(-10)
XCTAssertEqual(.noError, NSDecimalNormalize(&one, &ten, .plain))
Expand Down Expand Up @@ -558,6 +575,36 @@ class TestDecimal: XCTestCase {
XCTAssertEqual(.lossOfPrecision, NSDecimalNormalize(&large, &small, .plain))
XCTAssertEqual(small.exponent, 127)
XCTAssertEqual(large.exponent, 127)

// Normalise with loss of precision
let a = try XCTUnwrap(Decimal(string: "498.7509045"))
let b = try XCTUnwrap(Decimal(string: "8.453441368210501065891847765109162027"))

var aNormalized = a
var bNormalized = b
let normalizeError = NSDecimalNormalize(&aNormalized, &bNormalized, .plain)
XCTAssertEqual(normalizeError, NSDecimalNumber.CalculationError.lossOfPrecision)

XCTAssertEqual(aNormalized.exponent, -31)
XCTAssertEqual(aNormalized._mantissa.0, 0)
XCTAssertEqual(aNormalized._mantissa.1, 21760)
XCTAssertEqual(aNormalized._mantissa.2, 45355)
XCTAssertEqual(aNormalized._mantissa.3, 11455)
XCTAssertEqual(aNormalized._mantissa.4, 62709)
XCTAssertEqual(aNormalized._mantissa.5, 14050)
XCTAssertEqual(aNormalized._mantissa.6, 62951)
XCTAssertEqual(aNormalized._mantissa.7, 0)
XCTAssertEqual(bNormalized.exponent, -31)
XCTAssertEqual(bNormalized._mantissa.0, 56467)
XCTAssertEqual(bNormalized._mantissa.1, 17616)
XCTAssertEqual(bNormalized._mantissa.2, 59987)
XCTAssertEqual(bNormalized._mantissa.3, 21635)
XCTAssertEqual(bNormalized._mantissa.4, 5988)
XCTAssertEqual(bNormalized._mantissa.5, 63852)
XCTAssertEqual(bNormalized._mantissa.6, 1066)
XCTAssertEqual(bNormalized._mantissa.7, 1628)
XCTAssertEqual(a, aNormalized)
XCTAssertNotEqual(b, bNormalized) // b had a loss Of Precision when normalising
}

func test_NSDecimal() throws {
Expand Down