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[stdlib] BinaryInteger func word(at:) => var words: Words #8984

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Apr 25, 2017
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[stdlib] BinaryInteger func word(at:) => var words: Words #8984

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2750f59
[stdlib] Underscoring BinaryInteger.word(at:)
Apr 24, 2017
8fb0b5e
[stdlib] Implementing var words in terms of _word(at:)
Apr 24, 2017
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36 changes: 27 additions & 9 deletions stdlib/public/core/Integers.swift.gyb
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Original file line number Diff line number Diff line change
Expand Up @@ -1464,7 +1464,7 @@ public protocol BinaryInteger :
/// Returns the n-th word, counting from the least significant to most
/// significant, of this value's binary representation.
///
/// The `word(at:)` method returns negative values in two's complement
/// The `_word(at:)` method returns negative values in two's complement
/// representation, regardless of a type's underlying implementation. If `n`
/// is greater than the number of words in this value's current
/// representation, the result is `0` for positive numbers and `~0` for
Expand All @@ -1474,7 +1474,13 @@ public protocol BinaryInteger :
/// most significant. `n` must be greater than or equal to zero.
/// - Returns: An word-sized, unsigned integer with the bit pattern of the
/// n-th word of this value.
func word(at n: Int) -> UInt
func _word(at n: Int) -> UInt

// FIXME(integers): add doc comments
// FIXME: Should be `Words : Collection where Words.Iterator.Element == UInt`
// See <rdar://problem/31798916> for why it isn't.
associatedtype Words
var words: Words { get }

/// The number of bits in the current binary representation of this value.
///
Expand Down Expand Up @@ -1918,6 +1924,18 @@ extension BinaryInteger {
}
#endif

extension BinaryInteger {
// FIXME(integers): inefficient. Should get rid of _word(at:) and
// countRepresentedWords, and make `words` the basic operation.
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Do you want to use this to speed it up?

https://gist.github.com/dabrahams/976827a900b22689b09e14e7ffeecdcd

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I was thinking about CollectionOfOne<UInt>. But _UIntBuffer<UInt, UInt64> looks like a better solution for 32-bit platforms. Thanks!

public var words: [UInt] {
var result = [UInt]()
result.reserveCapacity(countRepresentedWords)
for i in 0..<self.countRepresentedWords {
result.append(_word(at: i))
}
return result
}
}

//===----------------------------------------------------------------------===//
//===--- FixedWidthInteger ------------------------------------------------===//
Expand Down Expand Up @@ -2306,7 +2324,7 @@ ${unsafeOperationComment(x.operator)}
@inline(__always)
public init<T : BinaryInteger>(extendingOrTruncating source: T) {
if Self.bitWidth <= ${word_bits} {
self = Self.init(_truncatingBits: source.word(at: 0))
self = Self.init(_truncatingBits: source._word(at: 0))
}
else {
var result: Self = source < (0 as T) ? ~0 : 0
Expand All @@ -2317,7 +2335,7 @@ ${unsafeOperationComment(x.operator)}
// that Self.bitWidth > ${word_bits}. Not masking results in
// infinite recursion.
result &<<= (${word_bits} as Self)
result |= Self(_truncatingBits: source.word(at: n))
result |= Self(_truncatingBits: source._word(at: n))
n -= 1
}

Expand Down Expand Up @@ -2865,7 +2883,7 @@ ${operatorComment(x.operator, True)}
}

@_transparent
public func word(at n: Int) -> UInt {
public func _word(at n: Int) -> UInt {
_precondition(n >= 0, "Negative word index")
if _fastPath(n < countRepresentedWords) {
let shift = UInt(n._value) &* ${word_bits}
Expand Down Expand Up @@ -3302,15 +3320,15 @@ public struct DoubleWidth<T : FixedWidthInteger>
fatalError()
}

public func word(at n: Int) -> UInt {
public func _word(at n: Int) -> UInt {
if T.bitWidth < ${word_bits} || T.bitWidth % ${word_bits} != 0 {
fatalError("word(at:) is not supported on this type")
fatalError("_word(at:) is not supported on this type")
}
// TODO: move to Int128 just like init(_builtinIntegerLiteral:) ?
let wordsInT = T.bitWidth / ${word_bits}
return (n < wordsInT) ?
_storage.low.word(at: n) :
_storage.high.word(at: n - wordsInT)
_storage.low._word(at: n) :
_storage.high._word(at: n - wordsInT)
}

public static var isSigned: Bool {
Expand Down
6 changes: 3 additions & 3 deletions test/Prototypes/BigInt.swift
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Expand Up @@ -122,7 +122,7 @@ public struct _BigInt<Word: FixedWidthInteger & UnsignedInteger> :
let wordRatio = UInt.bitWidth / Word.bitWidth
_sanityCheck(wordRatio != 0)
for i in 0..<source.countRepresentedWords {
var sourceWord = source.word(at: i)
var sourceWord = source._word(at: i)
for _ in 0..<wordRatio {
_data.append(Word(extendingOrTruncating: sourceWord))
sourceWord >>= Word.bitWidth
Expand Down Expand Up @@ -660,7 +660,7 @@ public struct _BigInt<Word: FixedWidthInteger & UnsignedInteger> :
}
}

public func word(at n: Int) -> UInt {
public func _word(at n: Int) -> UInt {
let ratio = UInt.bitWidth / Word.bitWidth
_sanityCheck(ratio != 0)

Expand Down Expand Up @@ -1293,7 +1293,7 @@ struct Bit : FixedWidthInteger, UnsignedInteger {
return self
}

func word(at n: Int) -> UInt {
func _word(at n: Int) -> UInt {
return UInt(value)
}

Expand Down
31 changes: 21 additions & 10 deletions test/stdlib/Integers.swift.gyb
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Expand Up @@ -33,12 +33,12 @@ extension FixedWidthInteger {
@discardableResult
// @_transparent
public mutating func replaceUWord(_ n: Int, with newBits: UInt) -> Bool {
let flippedBits = word(at: n) ^ newBits
let flippedBits = _word(at: n) ^ newBits
self ^= Self(_truncatingBits: flippedBits) << (${word_bits} * n)
if word(at: n) != newBits {
if _word(at: n) != newBits {
_log("###### overflow replacing word \(n) with \(newBits.hex)")
}
return word(at: n) == newBits
return _word(at: n) == newBits
}

/// a hex representation of every bit in the number
Expand All @@ -54,7 +54,7 @@ extension FixedWidthInteger {
if nibbles % 4 == 0 && nibbles != 0 {
result.insert("_", at: result.startIndex)
}
let lowUWord = x.word(at: 0)
let lowUWord = x._word(at: 0)
result.insert(
hexDigits[Int(lowUWord._value) & 0xF],
at: result.startIndex
Expand Down Expand Up @@ -495,16 +495,27 @@ tests.test("Basics") {

tests.test("word") {
let x = UDWord(Int.max)
expectEqual(Int.max._lowUWord, x.word(at: 0))
expectEqual(0, x.word(at: 1))
expectEqual(Int.max._lowUWord, x._word(at: 0))
expectEqual(0, x._word(at: 1))

let y = DWord(Int.min)
expectEqual(Int.min._lowUWord, y.word(at: 0))
expectEqual(~0, y.word(at: 1))
expectEqual(Int.min._lowUWord, y._word(at: 0))
expectEqual(~0, y._word(at: 1))

let z = UInt(~Int.min) + 1
expectEqual(Int.min._lowUWord, z.word(at: 0))
expectEqual(0, z.word(at: 1))
expectEqual(Int.min._lowUWord, z._word(at: 0))
expectEqual(0, z._word(at: 1))
}

tests.test("words") {
expectEqualSequence([UInt.max], (-1 as Int).words)
expectEqualSequence([UInt.max], (-1 as Int8).words)
expectEqualSequence([UInt.max], (-1 as Int16).words)
expectEqualSequence([UInt.max], (-1 as Int32).words)
expectEqualSequence([UInt.max], (-1 as Int64).words)

expectEqualSequence([1], 1.words)
expectEqualSequence([0], 0.words)
}

tests.test("multipliedFullWidth/UInt8") {
Expand Down