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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, *)
internal protocol _StringMetric: RopeMetric where Element == BigString._Chunk {
func distance(
from start: String.Index,
to end: String.Index,
in chunk: BigString._Chunk
) -> Int
func formIndex(
_ i: inout String.Index,
offsetBy distance: inout Int,
in chunk: BigString._Chunk
) -> (found: Bool, forward: Bool)
}
@available(macOS 13.3, iOS 16.4, watchOS 9.4, tvOS 16.4, *)
extension BigString {
internal struct _CharacterMetric: _StringMetric {
typealias Element = BigString._Chunk
typealias Summary = BigString.Summary
@inline(__always)
func size(of summary: Summary) -> Int {
summary.characters
}
func distance(
from start: String.Index,
to end: String.Index,
in chunk: BigString._Chunk
) -> Int {
chunk.characterDistance(from: start, to: end)
}
func formIndex(
_ i: inout String.Index,
offsetBy distance: inout Int,
in chunk: BigString._Chunk
) -> (found: Bool, forward: Bool) {
chunk.formCharacterIndex(&i, offsetBy: &distance)
}
func index(at offset: Int, in chunk: BigString._Chunk) -> String.Index {
precondition(offset < chunk.characterCount)
return chunk.wholeCharacters._index(at: offset)
}
}
internal struct _UnicodeScalarMetric: _StringMetric {
@inline(__always)
func size(of summary: Summary) -> Int {
summary.unicodeScalars
}
func distance(
from start: String.Index,
to end: String.Index,
in chunk: BigString._Chunk
) -> Int {
chunk.string.unicodeScalars.distance(from: start, to: end)
}
func formIndex(
_ i: inout String.Index,
offsetBy distance: inout Int,
in chunk: BigString._Chunk
) -> (found: Bool, forward: Bool) {
guard distance != 0 else {
i = chunk.string.unicodeScalars._index(roundingDown: i)
return (true, false)
}
if distance > 0 {
let end = chunk.string.endIndex
while distance > 0, i < end {
chunk.string.unicodeScalars.formIndex(after: &i)
distance &-= 1
}
return (distance == 0, true)
}
let start = chunk.string.startIndex
while distance < 0, i > start {
chunk.string.unicodeScalars.formIndex(before: &i)
distance &+= 1
}
return (distance == 0, false)
}
func index(at offset: Int, in chunk: BigString._Chunk) -> String.Index {
chunk.string.unicodeScalars.index(chunk.string.startIndex, offsetBy: offset)
}
}
internal struct _UTF8Metric: _StringMetric {
@inline(__always)
func size(of summary: Summary) -> Int {
summary.utf8
}
func distance(
from start: String.Index,
to end: String.Index,
in chunk: BigString._Chunk
) -> Int {
chunk.string.utf8.distance(from: start, to: end)
}
func formIndex(
_ i: inout String.Index,
offsetBy distance: inout Int,
in chunk: BigString._Chunk
) -> (found: Bool, forward: Bool) {
// Here we make use of the fact that the UTF-8 view of native Swift strings
// have O(1) index distance & offset calculations.
let offset = chunk.string.utf8.distance(from: chunk.string.startIndex, to: i)
if distance >= 0 {
let rest = chunk.utf8Count - offset
if distance > rest {
i = chunk.string.endIndex
distance -= rest
return (false, true)
}
i = chunk.string.utf8.index(i, offsetBy: distance)
distance = 0
return (true, true)
}
if offset + distance < 0 {
i = chunk.string.startIndex
distance += offset
return (false, false)
}
i = chunk.string.utf8.index(i, offsetBy: distance)
distance = 0
return (true, false)
}
func index(at offset: Int, in chunk: BigString._Chunk) -> String.Index {
chunk.string.utf8.index(chunk.string.startIndex, offsetBy: offset)
}
}
internal struct _UTF16Metric: _StringMetric {
@inline(__always)
func size(of summary: Summary) -> Int {
summary.utf16
}
func distance(
from start: String.Index,
to end: String.Index,
in chunk: BigString._Chunk
) -> Int {
chunk.string.utf16.distance(from: start, to: end)
}
func formIndex(
_ i: inout String.Index,
offsetBy distance: inout Int,
in chunk: BigString._Chunk
) -> (found: Bool, forward: Bool) {
if distance >= 0 {
if
distance <= chunk.utf16Count,
let r = chunk.string.utf16.index(
i, offsetBy: distance, limitedBy: chunk.string.endIndex
) {
i = r
distance = 0
return (true, true)
}
distance -= chunk.string.utf16.distance(from: i, to: chunk.string.endIndex)
i = chunk.string.endIndex
return (false, true)
}
if
distance.magnitude <= chunk.utf16Count,
let r = chunk.string.utf16.index(
i, offsetBy: distance, limitedBy: chunk.string.endIndex
) {
i = r
distance = 0
return (true, true)
}
distance += chunk.string.utf16.distance(from: chunk.string.startIndex, to: i)
i = chunk.string.startIndex
return (false, false)
}
func index(at offset: Int, in chunk: BigString._Chunk) -> String.Index {
chunk.string.utf16.index(chunk.string.startIndex, offsetBy: offset)
}
}
}
#endif
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