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[stdlib] Mark index encodings in String.UTF8View & UTF16View

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This commit is contained in:
Karoy Lorentey
2022-03-16 20:16:03 -07:00
parent 8ab2379946
commit 836bf9ad73
3 changed files with 38 additions and 24 deletions
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34
stdlib/public/core/StringUTF16View.swift
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@@ -141,7 +141,7 @@ extension String.UTF16View: BidirectionalCollection {
@inlinable @inline(__always)
public func index(after idx: Index) -> Index {
if _slowPath(_guts.isForeign) { return _foreignIndex(after: idx) }
if _guts.isASCII { return idx.nextEncoded }
if _guts.isASCII { return idx.nextEncoded._knownUTF8._knownUTF16 }
// For a BMP scalar (1-3 UTF-8 code units), advance past it. For a non-BMP
// scalar, use a transcoded offset first.
@@ -152,20 +152,24 @@ extension String.UTF16View: BidirectionalCollection {
let len = _guts.fastUTF8ScalarLength(startingAt: idx._encodedOffset)
if len == 4 && idx.transcodedOffset == 0 {
return idx.nextTranscoded
return idx.nextTranscoded._knownUTF8
}
return idx.strippingTranscoding.encoded(offsetBy: len)._scalarAligned
return idx
.strippingTranscoding
.encoded(offsetBy: len)
._scalarAligned
._knownUTF8
}
@inlinable @inline(__always)
public func index(before idx: Index) -> Index {
_precondition(!idx.isZeroPosition)
if _slowPath(_guts.isForeign) { return _foreignIndex(before: idx) }
if _guts.isASCII { return idx.priorEncoded }
if _guts.isASCII { return idx.priorEncoded._knownUTF8._knownUTF16 }
if idx.transcodedOffset != 0 {
_internalInvariant(idx.transcodedOffset == 1)
return idx.strippingTranscoding
return idx.strippingTranscoding._knownUTF8
}
let idx = _utf16AlignNativeIndex(idx)
@@ -173,12 +177,12 @@ extension String.UTF16View: BidirectionalCollection {
if len == 4 {
// 2 UTF-16 code units comprise this scalar; advance to the beginning and
// start mid-scalar transcoding
return idx.encoded(offsetBy: -len).nextTranscoded
return idx.encoded(offsetBy: -len).nextTranscoded._knownUTF8
}
// Single UTF-16 code unit
_internalInvariant((1...3) ~= len)
return idx.encoded(offsetBy: -len)._scalarAligned
return idx.encoded(offsetBy: -len)._scalarAligned._knownUTF8
}
public func index(_ i: Index, offsetBy n: Int) -> Index {
@@ -660,10 +664,14 @@ extension String.UTF16View {
// Trivial and common: start
if offset == 0 { return startIndex }
if _guts.isASCII { return Index(_encodedOffset: offset) }
if _guts.isASCII {
return Index(
_encodedOffset: offset
)._scalarAligned._knownUTF8._knownUTF16
}
guard _guts._useBreadcrumbs(forEncodedOffset: offset) else {
return _index(startIndex, offsetBy: offset)
return _index(startIndex, offsetBy: offset)._knownUTF8
}
// Simple and common: endIndex aka `length`.
@@ -699,9 +707,13 @@ extension String.UTF16View {
// Uncommon: final sub-scalar transcoded offset
if _slowPath(utf16I > utf16End) {
_internalInvariant(utf16Len == 2)
return Index(encodedOffset: readIdx, transcodedOffset: 1)
return Index(
encodedOffset: readIdx, transcodedOffset: 1
)._knownUTF8
}
return Index(_encodedOffset: readIdx &+ len)._scalarAligned
return Index(
_encodedOffset: readIdx &+ len
)._scalarAligned._knownUTF8
}
readIdx &+= len