Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

[SR-14384][SR-14974] Fix Decimal.ulp, nextUp, nextDown #3070

Merged
merged 4 commits into from
Sep 8, 2021
Merged

[SR-14384][SR-14974] Fix Decimal.ulp, nextUp, nextDown #3070

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
405aaec
Use 'Decimal.ulp' to compute 'nextUp' and 'nextDown'.
xwu Aug 29, 2021
e8c418c
[SR-14974] Fix 'Decimal.ulp' to reflect spacing between consecutive v…
xwu Aug 29, 2021
aed94d4
Fix a subtle bug in Decimal.ulp and adjust tests.
xwu Sep 5, 2021
376c6b2
Fix implementation of Decimal.nextUp.
xwu Sep 7, 2021
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
90 changes: 72 additions & 18 deletions Darwin/Foundation-swiftoverlay-Tests/TestDecimal.swift
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -208,21 +208,6 @@ class TestDecimal : XCTestCase {
XCTAssertEqual(11, sm5)
XCTAssertEqual(12, sm6)
XCTAssertEqual(13, sm7)

let ulp = explicit.ulp
XCTAssertEqual(0x7f, ulp.exponent)
XCTAssertEqual(1, ulp._length)
XCTAssertEqual(0, ulp._isNegative)
XCTAssertEqual(1, ulp._isCompact)
XCTAssertEqual(0, ulp._reserved)
XCTAssertEqual(1, ulp._mantissa.0)
XCTAssertEqual(0, ulp._mantissa.1)
XCTAssertEqual(0, ulp._mantissa.2)
XCTAssertEqual(0, ulp._mantissa.3)
XCTAssertEqual(0, ulp._mantissa.4)
XCTAssertEqual(0, ulp._mantissa.5)
XCTAssertEqual(0, ulp._mantissa.6)
XCTAssertEqual(0, ulp._mantissa.7)
}

func test_Maths() {
Expand Down Expand Up @@ -287,8 +272,6 @@ class TestDecimal : XCTestCase {
XCTAssertTrue(Decimal(2) < Decimal(3))
XCTAssertTrue(Decimal(3) > Decimal(2))
XCTAssertEqual(Decimal(-9), Decimal(1) - Decimal(10))
XCTAssertEqual(Decimal(3), Decimal(2).nextUp)
XCTAssertEqual(Decimal(2), Decimal(3).nextDown)
XCTAssertEqual(Decimal(1.234), abs(Decimal(1.234)))
XCTAssertEqual(Decimal(1.234), abs(Decimal(-1.234)))
if #available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *) {
Expand Down Expand Up @@ -608,8 +591,79 @@ class TestDecimal : XCTestCase {
}

func test_ULP() {
let x = 0.1 as Decimal
var x = 0.1 as Decimal
XCTAssertFalse(x.ulp > x)

x = .nan
XCTAssertTrue(x.ulp.isNaN)
XCTAssertTrue(x.nextDown.isNaN)
XCTAssertTrue(x.nextUp.isNaN)

x = .greatestFiniteMagnitude
XCTAssertEqual(x.ulp, Decimal(string: "1e127")!)
XCTAssertEqual(x.nextDown, x - Decimal(string: "1e127")!)
XCTAssertTrue(x.nextUp.isNaN)

// '4' is an important value to test because the max supported
// significand of this type is not 10 ** 38 - 1 but rather 2 ** 128 - 1,
// for which reason '4.ulp' is not equal to '1.ulp' despite having the
// same decimal exponent.
x = 4
XCTAssertEqual(x.ulp, Decimal(string: "1e-37")!)
XCTAssertEqual(x.nextDown, x - Decimal(string: "1e-37")!)
XCTAssertEqual(x.nextUp, x + Decimal(string: "1e-37")!)
XCTAssertEqual(x.nextDown.nextUp, x)
XCTAssertEqual(x.nextUp.nextDown, x)
XCTAssertNotEqual(x.nextDown, x)
XCTAssertNotEqual(x.nextUp, x)

// For similar reasons, '3.40282366920938463463374607431768211455',
// which has the same significand as 'Decimal.greatestFiniteMagnitude',
// is an important value to test because the distance to the next
// representable value is more than 'ulp' and instead requires
// incrementing '_exponent'.
x = Decimal(string: "3.40282366920938463463374607431768211455")!
XCTAssertEqual(x.ulp, Decimal(string: "0.00000000000000000000000000000000000001")!)
XCTAssertEqual(x.nextUp, Decimal(string: "3.4028236692093846346337460743176821146")!)
x = Decimal(string: "3.4028236692093846346337460743176821146")!
XCTAssertEqual(x.ulp, Decimal(string: "0.0000000000000000000000000000000000001")!)
XCTAssertEqual(x.nextDown, Decimal(string: "3.40282366920938463463374607431768211455")!)

x = 1
XCTAssertEqual(x.ulp, Decimal(string: "1e-38")!)
XCTAssertEqual(x.nextDown, x - Decimal(string: "1e-38")!)
XCTAssertEqual(x.nextUp, x + Decimal(string: "1e-38")!)
XCTAssertEqual(x.nextDown.nextUp, x)
XCTAssertEqual(x.nextUp.nextDown, x)
XCTAssertNotEqual(x.nextDown, x)
XCTAssertNotEqual(x.nextUp, x)

x = .leastNonzeroMagnitude
XCTAssertEqual(x.ulp, x)
XCTAssertEqual(x.nextDown, 0)
XCTAssertEqual(x.nextUp, x + x)
XCTAssertEqual(x.nextDown.nextUp, x)
XCTAssertEqual(x.nextUp.nextDown, x)
XCTAssertNotEqual(x.nextDown, x)
XCTAssertNotEqual(x.nextUp, x)

x = 0
XCTAssertEqual(x.ulp, Decimal(string: "1e-128")!)
XCTAssertEqual(x.nextDown, -Decimal(string: "1e-128")!)
XCTAssertEqual(x.nextUp, Decimal(string: "1e-128")!)
XCTAssertEqual(x.nextDown.nextUp, x)
XCTAssertEqual(x.nextUp.nextDown, x)
XCTAssertNotEqual(x.nextDown, x)
XCTAssertNotEqual(x.nextUp, x)

x = -1
XCTAssertEqual(x.ulp, Decimal(string: "1e-38")!)
XCTAssertEqual(x.nextDown, x - Decimal(string: "1e-38")!)
XCTAssertEqual(x.nextUp, x + Decimal(string: "1e-38")!)
XCTAssertEqual(x.nextDown.nextUp, x)
XCTAssertEqual(x.nextUp.nextDown, x)
XCTAssertNotEqual(x.nextDown, x)
XCTAssertNotEqual(x.nextUp, x)
}

func test_unconditionallyBridgeFromObjectiveC() {
Expand Down
92 changes: 84 additions & 8 deletions Darwin/Foundation-swiftoverlay/Decimal.swift
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -324,6 +324,57 @@ extension Decimal : Strideable {
}
}

private extension Decimal {
// Creates a value with zero exponent.
// (Used by `_powersOfTenDividingUInt128Max`.)
init(_length: UInt32, _isCompact: UInt32, _mantissa: (UInt16, UInt16, UInt16, UInt16, UInt16, UInt16, UInt16, UInt16)) {
self.init(_exponent: 0, _length: _length, _isNegative: 0, _isCompact: _isCompact,
_reserved: 0, _mantissa: _mantissa)
}
}

private let _powersOfTenDividingUInt128Max = [
/* 10**00 dividing UInt128.max is deliberately omitted. */
/* 10**01 */ Decimal(_length: 8, _isCompact: 1, _mantissa: (0x9999, 0x9999, 0x9999, 0x9999, 0x9999, 0x9999, 0x9999, 0x1999)),
/* 10**02 */ Decimal(_length: 8, _isCompact: 1, _mantissa: (0xf5c2, 0x5c28, 0xc28f, 0x28f5, 0x8f5c, 0xf5c2, 0x5c28, 0x028f)),
/* 10**03 */ Decimal(_length: 8, _isCompact: 1, _mantissa: (0x1893, 0x5604, 0x2d0e, 0x9db2, 0xa7ef, 0x4bc6, 0x8937, 0x0041)),
/* 10**04 */ Decimal(_length: 8, _isCompact: 1, _mantissa: (0x0275, 0x089a, 0x9e1b, 0x295e, 0x10cb, 0xbac7, 0x8db8, 0x0006)),
/* 10**05 */ Decimal(_length: 7, _isCompact: 1, _mantissa: (0x3372, 0x80dc, 0x0fcf, 0x8423, 0x1b47, 0xac47, 0xa7c5,0)),
/* 10**06 */ Decimal(_length: 7, _isCompact: 1, _mantissa: (0x3858, 0xf349, 0xb4c7, 0x8d36, 0xb5ed, 0xf7a0, 0x10c6,0)),
/* 10**07 */ Decimal(_length: 7, _isCompact: 1, _mantissa: (0xec08, 0x6520, 0x787a, 0xf485, 0xabca, 0x7f29, 0x01ad,0)),
/* 10**08 */ Decimal(_length: 7, _isCompact: 1, _mantissa: (0x4acd, 0x7083, 0xbf3f, 0x1873, 0xc461, 0xf31d, 0x002a,0)),
/* 10**09 */ Decimal(_length: 7, _isCompact: 1, _mantissa: (0x5447, 0x8b40, 0x2cb9, 0xb5a5, 0xfa09, 0x4b82, 0x0004,0)),
/* 10**10 */ Decimal(_length: 6, _isCompact: 1, _mantissa: (0xa207, 0x5ab9, 0xeadf, 0x5ef6, 0x7f67, 0x6df3,0,0)),
/* 10**11 */ Decimal(_length: 6, _isCompact: 1, _mantissa: (0xf69a, 0xef78, 0x4aaf, 0xbcb2, 0xbff0, 0x0afe,0,0)),
/* 10**12 */ Decimal(_length: 6, _isCompact: 1, _mantissa: (0x7f0f, 0x97f2, 0xa111, 0x12de, 0x7998, 0x0119,0,0)),
/* 10**13 */ Decimal(_length: 6, _isCompact: 0, _mantissa: (0x0cb4, 0xc265, 0x7681, 0x6849, 0x25c2, 0x001c,0,0)),
/* 10**14 */ Decimal(_length: 6, _isCompact: 1, _mantissa: (0x4e12, 0x603d, 0x2573, 0x70d4, 0xd093, 0x0002,0,0)),
/* 10**15 */ Decimal(_length: 5, _isCompact: 1, _mantissa: (0x87ce, 0x566c, 0x9d58, 0xbe7b, 0x480e,0,0,0)),
/* 10**16 */ Decimal(_length: 5, _isCompact: 1, _mantissa: (0xda61, 0x6f0a, 0xf622, 0xaca5, 0x0734,0,0,0)),
/* 10**17 */ Decimal(_length: 5, _isCompact: 1, _mantissa: (0x4909, 0xa4b4, 0x3236, 0x77aa, 0x00b8,0,0,0)),
/* 10**18 */ Decimal(_length: 5, _isCompact: 1, _mantissa: (0xa0e7, 0x43ab, 0xd1d2, 0x725d, 0x0012,0,0,0)),
/* 10**19 */ Decimal(_length: 5, _isCompact: 1, _mantissa: (0xc34a, 0x6d2a, 0x94fb, 0xd83c, 0x0001,0,0,0)),
/* 10**20 */ Decimal(_length: 4, _isCompact: 1, _mantissa: (0x46ba, 0x2484, 0x4219, 0x2f39,0,0,0,0)),
/* 10**21 */ Decimal(_length: 4, _isCompact: 1, _mantissa: (0xd3df, 0x83a6, 0xed02, 0x04b8,0,0,0,0)),
/* 10**22 */ Decimal(_length: 4, _isCompact: 1, _mantissa: (0x7b96, 0x405d, 0xe480, 0x0078,0,0,0,0)),
/* 10**23 */ Decimal(_length: 4, _isCompact: 1, _mantissa: (0x5928, 0xa009, 0x16d9, 0x000c,0,0,0,0)),
/* 10**24 */ Decimal(_length: 4, _isCompact: 1, _mantissa: (0x88ea, 0x299a, 0x357c, 0x0001,0,0,0,0)),
/* 10**25 */ Decimal(_length: 3, _isCompact: 1, _mantissa: (0xda7d, 0xd0f5, 0x1ef2,0,0,0,0,0)),
/* 10**26 */ Decimal(_length: 3, _isCompact: 1, _mantissa: (0x95d9, 0x4818, 0x0318,0,0,0,0,0)),
/* 10**27 */ Decimal(_length: 3, _isCompact: 0, _mantissa: (0xdbc8, 0x3a68, 0x004f,0,0,0,0,0)),
/* 10**28 */ Decimal(_length: 3, _isCompact: 1, _mantissa: (0xaf94, 0xec3d, 0x0007,0,0,0,0,0)),
/* 10**29 */ Decimal(_length: 2, _isCompact: 1, _mantissa: (0xf7f5, 0xcad2,0,0,0,0,0,0)),
/* 10**30 */ Decimal(_length: 2, _isCompact: 1, _mantissa: (0x4bfe, 0x1448,0,0,0,0,0,0)),
/* 10**31 */ Decimal(_length: 2, _isCompact: 1, _mantissa: (0x3acc, 0x0207,0,0,0,0,0,0)),
/* 10**32 */ Decimal(_length: 2, _isCompact: 1, _mantissa: (0xec47, 0x0033,0,0,0,0,0,0)),
/* 10**33 */ Decimal(_length: 2, _isCompact: 1, _mantissa: (0x313a, 0x0005,0,0,0,0,0,0)),
/* 10**34 */ Decimal(_length: 1, _isCompact: 1, _mantissa: (0x84ec,0,0,0,0,0,0,0)),
/* 10**35 */ Decimal(_length: 1, _isCompact: 1, _mantissa: (0x0d4a,0,0,0,0,0,0,0)),
/* 10**36 */ Decimal(_length: 1, _isCompact: 0, _mantissa: (0x0154,0,0,0,0,0,0,0)),
/* 10**37 */ Decimal(_length: 1, _isCompact: 1, _mantissa: (0x0022,0,0,0,0,0,0,0)),
/* 10**38 */ Decimal(_length: 1, _isCompact: 1, _mantissa: (0x0003,0,0,0,0,0,0,0))
]

// The methods in this extension exist to match the protocol requirements of
// FloatingPoint, even if we can't conform directly.
//
Expand Down Expand Up @@ -550,22 +601,47 @@ extension Decimal {
}

public var ulp: Decimal {
if !self.isFinite { return Decimal.nan }
guard isFinite else { return .nan }

let exponent: Int32
if isZero {
exponent = .min
} else {
let significand_ = significand
let shift =
_powersOfTenDividingUInt128Max.firstIndex { significand_ > $0 }
?? _powersOfTenDividingUInt128Max.count
exponent = _exponent &- Int32(shift)
}

return Decimal(
_exponent: _exponent, _length: 1, _isNegative: 0, _isCompact: 1,
_exponent: max(exponent, -128), _length: 1, _isNegative: 0, _isCompact: 1,
_reserved: 0, _mantissa: (0x0001, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000))
}

public var nextUp: Decimal {
return self + Decimal(
_exponent: _exponent, _length: 1, _isNegative: 0, _isCompact: 1,
_reserved: 0, _mantissa: (0x0001, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000))
if _isNegative == 1 {
if _exponent > -128
&& (_mantissa.0, _mantissa.1, _mantissa.2, _mantissa.3) == (0x999a, 0x9999, 0x9999, 0x9999)
&& (_mantissa.4, _mantissa.5, _mantissa.6, _mantissa.7) == (0x9999, 0x9999, 0x9999, 0x1999) {
return Decimal(
_exponent: _exponent &- 1, _length: 8, _isNegative: 1, _isCompact: 1,
_reserved: 0, _mantissa: (0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff))
}
} else {
if _exponent < 127
&& (_mantissa.0, _mantissa.1, _mantissa.2, _mantissa.3) == (0xffff, 0xffff, 0xffff, 0xffff)
&& (_mantissa.4, _mantissa.5, _mantissa.6, _mantissa.7) == (0xffff, 0xffff, 0xffff, 0xffff) {
return Decimal(
_exponent: _exponent &+ 1, _length: 8, _isNegative: 0, _isCompact: 1,
_reserved: 0, _mantissa: (0x999a, 0x9999, 0x9999, 0x9999, 0x9999, 0x9999, 0x9999, 0x1999))
}
}
return self + ulp
}

public var nextDown: Decimal {
return self - Decimal(
_exponent: _exponent, _length: 1, _isNegative: 0, _isCompact: 1,
_reserved: 0, _mantissa: (0x0001, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000))
return -(-self).nextUp
}

/// The IEEE 754 "class" of this type.
Expand Down
Loading