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//===--- BucketSort.swift -------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2021 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
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
// This benchmark demonstrates the benefits of ExistentialSpecializer
// optimization pass. It's a generic version of the classic BucketSort algorithm
// adapted from an original implementation from the Swift Algorithm Club.
// See https://en.wikipedia.org/wiki/Bucket_sort and
// https://github.com/raywenderlich/swift-algorithm-club/tree/master/Bucket%20Sort
//
// It sorts an array of generic `SortableItem`s. If the type of `sortingAlgo`
// is not known to the call site at line 89, the `sort` method can not be
// specialized to integer array sorting, which will lead to a huge performance
// loss. Since `SortingAlgorithm` and `InsertionSort` are declared to be
// `public` and the lines 88-90 can not be inlined in `bucketSort` (due to
// inlining heuristic limitations), compiler without ExistentialSpecializer
// optimization can not achieve this feat. With ExistentialSpecializer which
// enables generic specialization recursively in a call chain, we're able to
// specialize line 89 for `InsertionSort` on integers.
import TestsUtils
public let benchmarks =
BenchmarkInfo(
name: "BucketSort",
runFunction: run_BucketSort,
tags: [.validation, .algorithm],
setUpFunction: { blackHole(buckets) }
)
public protocol IntegerConvertible {
func convertToInt() -> Int
}
extension Int: IntegerConvertible, SortableItem {
public func convertToInt() -> Int {
return self
}
}
public protocol SortableItem: IntegerConvertible, Comparable { }
public protocol SortingAlgorithm {
func sort<T: SortableItem>(_ items: [T]) -> [T]
}
public struct InsertionSort: SortingAlgorithm {
public func sort<T: SortableItem>(_ items: [T]) -> [T] {
var sortedItems = items
for i in 0 ..< sortedItems.count {
var j = i
while j > 0 && sortedItems[j-1] > sortedItems[j] {
let temp = sortedItems[j-1]
sortedItems[j-1] = sortedItems[j]
sortedItems[j] = temp
j -= 1
}
}
return sortedItems
}
}
func distribute<T>(_ item: T, bucketArray: inout [Bucket<T>]) {
let val = item.convertToInt()
let capacity = bucketArray.first!.capacity
let index = val / capacity
bucketArray[index].add(item)
}
struct Bucket<T: SortableItem> {
var items: [T]
let capacity: Int
init(capacity: Int) {
self.capacity = capacity
items = [T]()
}
mutating func add(_ item: T) {
if items.count < capacity {
items.append(item)
}
}
func sort(_ sortingAlgo: SortingAlgorithm) -> [T] {
return sortingAlgo.sort(items)
}
}
func bucketSort<T>(
_ items: [T], sortingAlgorithm: SortingAlgorithm, bucketArray: [Bucket<T>]
) -> [T] {
var copyBucketArray = bucketArray
for item in items {
distribute(item, bucketArray: ©BucketArray)
}
var sortedArray = [T]()
for bucket in copyBucketArray {
sortedArray += bucket.sort(sortingAlgorithm)
}
return sortedArray
}
func isAscending(_ a: [Int]) -> Bool {
return zip(a, a.dropFirst()).allSatisfy(<=)
}
let items: [Int] = {
var g = SplitMix64(seed: 42)
return (0..<10_000).map {_ in Int.random(in: 0..<1000, using: &g) }
}()
let buckets: [Bucket<Int>] = {
let bucketCount = 10
let maxValue = items.max()!.convertToInt()
let maxCapacity = Int(
(Double(maxValue + 1) / Double(bucketCount)).rounded(.up))
return (0..<bucketCount).map { _ in Bucket<Int>(capacity: maxCapacity) }
}()
@inline(never)
func run_BucketSort(_ n : Int) {
for _ in 0..<n {
let sortedArray = bucketSort(
items, sortingAlgorithm: InsertionSort(), bucketArray: buckets)
check(isAscending(sortedArray))
}
}
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