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[string] Hoist UTF8View fast-path for known ASCII #14052

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Merged
merged 1 commit into from
Jan 23, 2018
Merged

[string] Hoist UTF8View fast-path for known ASCII #14052

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28 changes: 12 additions & 16 deletions stdlib/public/core/StringUTF8.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -484,32 +484,28 @@ extension String.UTF8View.Iterator : IteratorProtocol {

@_inlineable // FIXME(sil-serialize-all)
public mutating func next() -> Unicode.UTF8.CodeUnit? {
if _slowPath(_nextOffset == _endOffset) {
if _slowPath(_buffer.isEmpty) {
return nil
}
}
if _guts.isASCII {
defer { _nextOffset += 1 }
return _guts._unmanagedASCIIView.buffer[_nextOffset]
}

if _fastPath(!_buffer.isEmpty) {
return _buffer.removeFirst()
}
if _nextOffset == _endOffset { return nil }
return _fillBuffer()
}

@_versioned
@inline(never)
internal mutating func _fillBuffer() -> Unicode.UTF8.CodeUnit {
_sanityCheck(_buffer.isEmpty)
_sanityCheck(_nextOffset < _endOffset)
_sanityCheck(!_guts.isASCII, "next() already checks for known ASCII")
defer { _fixLifetime(_guts) }
if _guts.isASCII {
// FIXME: Measure if it's worth inlining this path
let ascii = _guts._unmanagedASCIIView.buffer
let result = ascii[_nextOffset]
_nextOffset += 1
let fillCount = min(_buffer.capacity, _endOffset - _nextOffset)
for _ in 0 ..< fillCount {
_buffer.append(ascii[_nextOffset])
_nextOffset += 1
}
return result
}
if _guts._isContiguous {
if _fastPath(_guts._isContiguous) {
return _fillBuffer(from: _guts._unmanagedUTF16View)
}
return _fillBuffer(from: _guts._asOpaque())
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