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Fix NSDecimalPower(_:_:_:_:) behavior #4799

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Fix NSDecimalPower(_:_:_:_:) behavior #4799

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9eead0c
Fix `NSDecimalPower(_:_:_:_:)` behavior
Oschly Jul 22, 2023
8da81c0
Improve tests, compare to p, not to the absPower
Oschly Jul 30, 2023
5e0a3f5
Merge branch 'apple:main' into main
Oschly Dec 21, 2023
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35 changes: 24 additions & 11 deletions Sources/Foundation/Decimal.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -1801,7 +1801,7 @@ public func NSDecimalPower(_ result: UnsafeMutablePointer<Decimal>, _ number: Un
return .overflow
}
NSDecimalCopy(result,number)
return result.pointee.power(UInt(power), roundingMode:roundingMode)
return result.pointee.power(power, roundingMode:roundingMode)
}

public func NSDecimalMultiplyByPowerOf10(_ result: UnsafeMutablePointer<Decimal>, _ number: UnsafePointer<Decimal>, _ power: Int16, _ roundingMode: NSDecimalNumber.RoundingMode) -> NSDecimalNumber.CalculationError {
Expand Down Expand Up @@ -2242,27 +2242,27 @@ extension Decimal {
_exponent = newExponent
return .noError
}
fileprivate mutating func power(_ p:UInt, roundingMode:RoundingMode) -> CalculationError {
fileprivate mutating func power(_ p:Int, roundingMode:RoundingMode) -> CalculationError {
if isNaN {
return .overflow
}
var power = p
if power == 0 {
if p == 0 {
_exponent = 0
_length = 1
_isNegative = 0
self[0] = 1
_isCompact = 1
return .noError
} else if power == 1 {
} else if p == 1 || isZero {
return .noError
}

var absPower = abs(p)
var temporary = Decimal(1)
var error:CalculationError = .noError

while power > 1 {
if power % 2 == 1 {
while absPower > 1 {
if absPower % 2 == 1 {
let previousError = error
var leftOp = temporary
error = NSDecimalMultiply(&temporary, &leftOp, &self, roundingMode)
Expand All @@ -2275,9 +2275,9 @@ extension Decimal {
setNaN()
return error
}
power -= 1
absPower -= 1
}
if power != 0 {
if absPower != 0 {
let previousError = error
var leftOp = self
var rightOp = self
Expand All @@ -2291,13 +2291,26 @@ extension Decimal {
setNaN()
return error
}
power /= 2
absPower /= 2
}
}
let previousError = error
var rightOp = self
error = NSDecimalMultiply(&self, &temporary, &rightOp, roundingMode)


// if power is negative, use multiplicative inverse
if p < 0 {
var leftOp = Decimal(1)
var rightOp = self

error = NSDecimalDivide(
&self,
&leftOp,
&rightOp,
roundingMode
)
}

if previousError != .noError { // FIXME is this the intent?
error = previousError
}
Expand Down
27 changes: 27 additions & 0 deletions Tests/Foundation/Tests/TestDecimal.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -670,6 +670,32 @@ class TestDecimal: XCTestCase {
XCTAssertEqual(1679616, negativeSix.raising(toPower:8).intValue)
XCTAssertEqual(-10077696, negativeSix.raising(toPower:9).intValue)
}

func test_NegativePowers() {
let six = NSDecimalNumber(integerLiteral: 6)

XCTAssertEqual(1/6 as NSDecimalNumber, six.raising(toPower: -1))
XCTAssertEqual(1/36 as NSDecimalNumber, six.raising(toPower: -2))
XCTAssertEqual(1/216 as NSDecimalNumber, six.raising(toPower: -3))
XCTAssertEqual(1/1296 as NSDecimalNumber, six.raising(toPower: -4))
XCTAssertEqual(1/7776 as NSDecimalNumber, six.raising(toPower: -5))
XCTAssertEqual(1/46656 as NSDecimalNumber, six.raising(toPower: -6))
XCTAssertEqual(1/279936 as NSDecimalNumber, six.raising(toPower: -7))
XCTAssertEqual(1/1679616 as NSDecimalNumber, six.raising(toPower: -8))
XCTAssertEqual(1/10077696 as NSDecimalNumber, six.raising(toPower: -9))

let negativeSix = NSDecimalNumber(integerLiteral: -6)

XCTAssertEqual(-1/6 as NSDecimalNumber, negativeSix.raising(toPower: -1))
XCTAssertEqual(1/36 as NSDecimalNumber, negativeSix.raising(toPower: -2))
XCTAssertEqual(-1/216 as NSDecimalNumber, negativeSix.raising(toPower: -3))
XCTAssertEqual(1/1296 as NSDecimalNumber, negativeSix.raising(toPower: -4))
XCTAssertEqual(-1/7776 as NSDecimalNumber, negativeSix.raising(toPower: -5))
XCTAssertEqual(1/46656 as NSDecimalNumber, negativeSix.raising(toPower: -6))
XCTAssertEqual(-1/279936 as NSDecimalNumber, negativeSix.raising(toPower: -7))
XCTAssertEqual(1/1679616 as NSDecimalNumber, negativeSix.raising(toPower: -8))
XCTAssertEqual(-1/10077696 as NSDecimalNumber, negativeSix.raising(toPower: -9))
}

func test_RepeatingDivision() {
let repeatingNumerator = Decimal(16)
Expand Down Expand Up @@ -1546,6 +1572,7 @@ class TestDecimal: XCTestCase {
("test_Normalise", test_Normalise),
("test_NSDecimal", test_NSDecimal),
("test_PositivePowers", test_PositivePowers),
("test_NegativePowers", test_NegativePowers),
("test_RepeatingDivision", test_RepeatingDivision),
("test_Round", test_Round),
("test_ScanDecimal", test_ScanDecimal),
Expand Down