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[SR-6671] Decimal.leastNonzeroMagnitude, leastNormalMagnitude should have -128 exponent #1386

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[SR-6671] Decimal.leastNonzeroMagnitude, leastNormalMagnitude should have -128 exponent #1386

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6976c58
Fix exponents for least magnitudes of Decimal
takasek Dec 28, 2017
03ba584
Fix tests for Decimal to ensure truly least magnitudes
takasek Dec 28, 2017
fda88d2
Add tests for underflowing limit of Decimal.leastMagnitude, overflowi…
takasek Jan 5, 2018
7a53e0d
Use more descriptive way to construct Decimal's least/greatest magnit…
takasek Jan 5, 2018
a40cc5c
Fix tests for serializing Decimal magnitude
takasek Jan 5, 2018
effcd17
Merge branch 'master' into sr-6671-decimal-least-exponent
takasek Nov 24, 2018
49503c6
Merge branch 'master' into sr-6671-decimal-least-exponent
takasek Mar 23, 2019
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8 changes: 4 additions & 4 deletions Foundation/Decimal.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -101,31 +101,31 @@ public struct Decimal {

extension Decimal {
public static let leastFiniteMagnitude = Decimal(
_exponent: 127,
_exponent: Int32(Int8.max),
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What do you think of such expression change?

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What's going on here, and where did this property come from? "Magnitudes" are always non-negative, but this is a huge negative number. I don't know why this property even exists, but the name and documentation are extremely misleading.

(@takasek This is tangential to your change, but this is the first I've seen this).

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Sorry, I haven't been respond for long time...

Referring to the code, _exponent has a precondition to conform Int8. I intend to describe the precondition.
https://github.com/apple/swift-corelibs-foundation/blob/a40cc5cb3159bf64d70cb657131a01272dc988e3/Foundation/Decimal.swift#L22-L28

More fundamental solution is to change public var _exponent: Int32 into public var _exponent: Int8 but I have no idea of the impact.

_length: 8,
_isNegative: 1,
_isCompact: 1,
_reserved: 0,
_mantissa: (0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff)
)
public static let greatestFiniteMagnitude = Decimal(
_exponent: 127,
_exponent: Int32(Int8.max),
_length: 8,
_isNegative: 0,
_isCompact: 1,
_reserved: 0,
_mantissa: (0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff)
)
public static let leastNormalMagnitude = Decimal(
_exponent: -127,
_exponent: Int32(Int8.min),
_length: 1,
_isNegative: 0,
_isCompact: 1,
_reserved: 0,
_mantissa: (0x0001, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000)
)
public static let leastNonzeroMagnitude = Decimal(
_exponent: -127,
_exponent: Int32(Int8.min),
_length: 1,
_isNegative: 0,
_isCompact: 1,
Expand Down
23 changes: 21 additions & 2 deletions TestFoundation/TestDecimal.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,8 @@ class TestDecimal: XCTestCase {
("test_doubleValue", test_doubleValue),
("test_NSDecimalNumberValues", test_NSDecimalNumberValues),
("test_bridging", test_bridging),
("test_LeastMagnitude", test_LeastMagnitude),
("test_GreatestMagnitude", test_GreatestMagnitude),
]
}

Expand Down Expand Up @@ -167,9 +169,9 @@ class TestDecimal: XCTestCase {
XCTAssertEqual(smallest, Decimal.leastFiniteMagnitude)
let biggest = Decimal(_exponent: 127, _length: 8, _isNegative: 0, _isCompact: 1, _reserved: 0, _mantissa: (UInt16.max, UInt16.max, UInt16.max, UInt16.max, UInt16.max, UInt16.max, UInt16.max, UInt16.max))
XCTAssertEqual(biggest, Decimal.greatestFiniteMagnitude)
let leastNormal = Decimal(_exponent: -127, _length: 1, _isNegative: 0, _isCompact: 1, _reserved: 0, _mantissa: (1, 0, 0, 0, 0, 0, 0, 0))
let leastNormal = Decimal(_exponent: -128, _length: 1, _isNegative: 0, _isCompact: 1, _reserved: 0, _mantissa: (1, 0, 0, 0, 0, 0, 0, 0))
XCTAssertEqual(leastNormal, Decimal.leastNormalMagnitude)
let leastNonzero = Decimal(_exponent: -127, _length: 1, _isNegative: 0, _isCompact: 1, _reserved: 0, _mantissa: (1, 0, 0, 0, 0, 0, 0, 0))
let leastNonzero = Decimal(_exponent: -128, _length: 1, _isNegative: 0, _isCompact: 1, _reserved: 0, _mantissa: (1, 0, 0, 0, 0, 0, 0, 0))
XCTAssertEqual(leastNonzero, Decimal.leastNonzeroMagnitude)
let pi = Decimal(_exponent: -38, _length: 8, _isNegative: 0, _isCompact: 1, _reserved: 0, _mantissa: (0x6623, 0x7d57, 0x16e7, 0xad0d, 0xaf52, 0x4641, 0xdfa7, 0xec58))
XCTAssertEqual(pi, Decimal.pi)
Expand Down Expand Up @@ -761,6 +763,23 @@ class TestDecimal: XCTestCase {
XCTAssertEqual(1, negativeSix.raising(toPower: 0))
}

func test_LeastMagnitude() {
var result = Decimal()

var leastNormal = Decimal.leastNormalMagnitude
XCTAssertEqual(.underflow, NSDecimalMultiplyByPowerOf10(&result, &leastNormal, -1, .plain))

var leastNonzero = Decimal.leastNonzeroMagnitude
XCTAssertEqual(.underflow, NSDecimalMultiplyByPowerOf10(&result, &leastNonzero, -1, .plain))
}

func test_GreatestMagnitude() {
var result = Decimal()

var greatest = Decimal.greatestFiniteMagnitude
XCTAssertEqual(.overflow, NSDecimalMultiplyByPowerOf10(&result, &greatest, 1, .plain))
}

func test_doubleValue() {
XCTAssertEqual(NSDecimalNumber(decimal:Decimal(0)).doubleValue, 0)
XCTAssertEqual(NSDecimalNumber(decimal:Decimal(1)).doubleValue, 1)
Expand Down
4 changes: 2 additions & 2 deletions TestFoundation/TestJSONSerialization.swift
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Expand Up @@ -1301,8 +1301,8 @@ extension TestJSONSerialization {
func test_serialize_Decimal() {
XCTAssertEqual(try trySerialize([-Decimal.leastFiniteMagnitude]), "[3402823669209384634633746074317682114550000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000]")
XCTAssertEqual(try trySerialize([Decimal.leastFiniteMagnitude]), "[-3402823669209384634633746074317682114550000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000]")
XCTAssertEqual(try trySerialize([-Decimal.leastNonzeroMagnitude]), "[-0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001]")
XCTAssertEqual(try trySerialize([Decimal.leastNonzeroMagnitude]), "[0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001]")
XCTAssertEqual(try trySerialize([-Decimal.leastNonzeroMagnitude]), "[-0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001]")
XCTAssertEqual(try trySerialize([Decimal.leastNonzeroMagnitude]), "[0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001]")
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These tests failed because of changes in this PR.

XCTAssertEqual(try trySerialize([-Decimal.greatestFiniteMagnitude]), "[-3402823669209384634633746074317682114550000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000]")
XCTAssertEqual(try trySerialize([Decimal.greatestFiniteMagnitude]), "[3402823669209384634633746074317682114550000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000]")
XCTAssertEqual(try trySerialize([Decimal(Int8.min), Decimal(Int8(0)), Decimal(Int8.max)]), "[-128,0,127]")
Expand Down