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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift Collections open source project
//
// Copyright (c) 2023 - 2024 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
//
//===----------------------------------------------------------------------===//
#if swift(>=5.8)
@available(macOS 13.3, iOS 16.4, watchOS 9.4, tvOS 16.4, *)
extension UInt8 {
/// Returns true if this is a leading code unit in the UTF-8 encoding of a Unicode scalar that
/// is outside the BMP.
var _isUTF8NonBMPLeadingCodeUnit: Bool { self >= 0b11110000 }
}
@available(macOS 13.3, iOS 16.4, watchOS 9.4, tvOS 16.4, *)
extension BigString._Chunk {
func characterDistance(from start: String.Index, to end: String.Index) -> Int {
let firstBreak = self.firstBreak
let (start, a) = start < firstBreak ? (firstBreak, 1) : (start, 0)
let (end, b) = end < firstBreak ? (firstBreak, 1) : (end, 0)
let d = wholeCharacters.distance(from: start, to: end)
return d + a - b
}
/// If this returns false, the next position is on the first grapheme break following this
/// chunk.
func formCharacterIndex(after i: inout String.Index) -> Bool {
if i >= lastBreak {
i = string.endIndex
return false
}
let first = firstBreak
if i < first {
i = first
return true
}
wholeCharacters.formIndex(after: &i)
return true
}
/// If this returns false, the right position is `distance` steps from the first grapheme break
/// following this chunk if `distance` was originally positive. Otherwise the right position is
/// `-distance` steps from the first grapheme break preceding this chunk.
func formCharacterIndex(
_ i: inout String.Index, offsetBy distance: inout Int
) -> (found: Bool, forward: Bool) {
if distance == 0 {
if i < firstBreak {
i = string.startIndex
return (false, false)
}
if i >= lastBreak {
i = lastBreak
return (true, false)
}
i = wholeCharacters._index(roundingDown: i)
return (true, false)
}
if distance > 0 {
if i >= lastBreak {
i = string.endIndex
distance -= 1
return (false, true)
}
if i < firstBreak {
i = firstBreak
distance -= 1
if distance == 0 { return (true, true) }
}
if
distance <= characterCount,
let r = wholeCharacters.index(i, offsetBy: distance, limitedBy: string.endIndex)
{
i = r
distance = 0
return (i < string.endIndex, true)
}
distance -= wholeCharacters.distance(from: i, to: lastBreak) + 1
i = string.endIndex
return (false, true)
}
if i <= firstBreak {
i = string.startIndex
if i == firstBreak { distance += 1 }
return (false, false)
}
if i > lastBreak {
i = lastBreak
distance += 1
if distance == 0 { return (true, false) }
}
if
distance.magnitude <= characterCount,
let r = self.wholeCharacters.index(i, offsetBy: distance, limitedBy: firstBreak)
{
i = r
distance = 0
return (true, false)
}
distance += self.wholeCharacters.distance(from: firstBreak, to: i)
i = string.startIndex
return (false, false)
}
}
#endif
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