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Improving the performance of String.UTF8View

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This commit is contained in:
Max Moiseev
2017-03-30 10:22:30 -07:00
parent 969b4814e2
commit cd98994b9d
1 changed files with 12 additions and 4 deletions
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16
stdlib/public/core/StringUTF8.swift
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@@ -190,6 +190,13 @@ extension String {
self._endIndex = e
}
// If not overridden, the default implementation provided by the Collection
// would be used, which unnecessarily penalizes algorithms that use
// UTF8View as a Sequence.
public var underestimatedCount: Int {
return _core.count
}
/// A position in a string's `UTF8View` instance.
///
/// You can convert between indices of the different string views by using
@@ -254,13 +261,13 @@ extension String {
/// A Buffer value with the high byte set
internal static var _bufferHiByte: Buffer {
return 0xFF &<< numericCast((MemoryLayout<Buffer>.size &- 1) &* 8)
return 0xFF &<< ((MemoryLayout<Buffer>.size &- 1) &* 8)
}
/// Consume a byte of the given buffer: shift out the low byte
/// and put FF in the high byte
internal static func _nextBuffer(after thisBuffer: Buffer) -> Buffer {
return (thisBuffer &>> 8) | _bufferHiByte
return (thisBuffer &>> (8 as Buffer)) | _bufferHiByte
}
/// The position of `self`, rounded up to the nearest unicode
@@ -296,7 +303,7 @@ extension String {
public func index(after i: Index) -> Index {
// FIXME: swift-3-indexing-model: range check i?
let currentUnit = UTF8.CodeUnit(extendingOrTruncating: i._buffer)
let hiNibble = currentUnit &>> 4
let hiNibble = currentUnit &>> (4 as UTF8.CodeUnit)
// Amounts to increment the UTF-16 index based on the high nibble of a
// UTF-8 code unit. If the high nibble is:
@@ -312,7 +319,8 @@ extension String {
// Map the high nibble of the current code unit into the
// amount by which to increment the UTF-16 index.
let increment = (u16Increments &>> numericCast(hiNibble &<< 1)) & 0x3
let increment = (u16Increments &>>
Int(extendingOrTruncating: hiNibble &<< (1 as UTF8.CodeUnit))) & 0x3
let nextCoreIndex = i._coreIndex &+ increment
let nextBuffer = Index._nextBuffer(after: i._buffer)