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[stdlib] Specialized String's Generator

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Specializing String's Generator yields a significant performance
improvement.

Swift SVN r23998
This commit is contained in:
Maxwell Swadling
2014-12-18 00:12:32 +00:00
parent 7cc8dfd59d
commit c2aa030c29
1 changed files with 41 additions and 5 deletions
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46
stdlib/core/StringUnicodeScalarView.swift
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@@ -138,8 +138,25 @@ extension String {
/// A type whose instances can produce the elements of this
/// sequence, in order.
public struct Generator : GeneratorType {
init(_ _base: _StringCore.Generator) {
self._base = _base
init(_ _base: _StringCore) {
if _base.hasContiguousStorage {
self._baseSet = true
if _base.isASCII {
self._ascii = true
self._asciiBase = UnsafeBufferPointer<UInt8>(
start: UnsafePointer(_base._baseAddress),
count: _base.count).generate()
} else {
self._ascii = false
self._base = UnsafeBufferPointer<UInt16>(
start: UnsafePointer(_base._baseAddress),
count: _base.count).generate()
}
} else {
self._ascii = false
self._baseSet = false
self._generator = _base.generate()
}
}
/// Advance to the next element and return it, or `nil` if no next
@@ -148,7 +165,22 @@ extension String {
/// Requires: no preceding call to `self.next()` has returned
/// `nil`.
public mutating func next() -> UnicodeScalar? {
switch _decoder.decode(&self._base) {
var result: UnicodeDecodingResult
if _baseSet {
if _ascii {
switch self._asciiBase.next() {
case let .Some(x):
result = .Result(UnicodeScalar(x))
case .None:
result = .EmptyInput
}
} else {
result = _decoder.decode(&(self._base!))
}
} else {
result = _decoder.decode(&(self._generator!))
}
switch result {
case .Result(let us):
return us
case .EmptyInput:
@@ -158,7 +190,11 @@ extension String {
}
}
var _decoder: UTF16 = UTF16()
var _base: _StringCore.Generator
let _baseSet: Bool
let _ascii: Bool
var _asciiBase: UnsafeBufferPointerGenerator<UInt8>!
var _base: UnsafeBufferPointerGenerator<UInt16>!
var _generator: IndexingGenerator<_StringCore>!
}
/// Return a *generator* over the `UnicodeScalar`\ s that comprise
@@ -166,7 +202,7 @@ extension String {
///
/// Complexity: O(1)
public func generate() -> Generator {
return Generator(_core.generate())
return Generator(_core)
}
/// Returns a mirror that reflects `self`.