DictTest.swift

//===--- DictTest.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
//
//===----------------------------------------------------------------------===//

import TestsUtils


public let benchmarks = [
  BenchmarkInfo(name: "Dictionary", runFunction: run_Dictionary,
    tags: [.validation, .api, .Dictionary],
    setUpFunction: { blackHole(half) },
    legacyFactor: 5),
  BenchmarkInfo(name: "DictionaryOfObjects",
    runFunction: run_DictionaryOfObjects,
    tags: [.validation, .api, .Dictionary],
    setUpFunction: { blackHole(halfObjects) },
    legacyFactor: 5),
]

let text = [
    // Text from http://en.wikipedia.org/wiki/Hash_table
    "hash", "table",
      "in", "computing", "a", "hash", "table", "also", "hash", "map", "is",
      "a", "data", "structure", "used", "to", "implement", "an", "associative",
      "array", "a", "structure", "that", "can", "map", "keys", "to", "values",
      "a", "hash", "table", "uses", "a", "hash", "function", "to", "compute",
      "an", "index", "into", "an", "array", "of", "buckets", "or", "slots",
      "from", "which", "the", "correct", "value", "can", "be", "found",
      "ideally", "the", "hash", "function", "will", "assign", "each", "key",
      "to", "a", "unique", "bucket", "but", "this", "situation", "is",
      "rarely", "achievable", "in", "practice", "usually", "some", "keys",
      "will", "hash", "to", "the", "same", "bucket", "instead", "most", "hash",
      "table", "designs", "assume", "that", "hash", "collisions", "different",
      "keys", "that", "are", "assigned", "by", "the", "hash", "function", "to",
      "the", "same", "bucket", "will", "occur", "and", "must", "be",
      "accommodated", "in", "some", "way", "in", "a", "well", "dimensioned",
      "hash", "table", "the", "average", "cost", "number", "of",
      "instructions", "for", "each", "lookup", "is", "independent", "of",
      "the", "number", "of", "elements", "stored", "in", "the", "table",
      "many", "hash", "table", "designs", "also", "allow", "arbitrary",
      "insertions", "and", "deletions", "of", "key", "value", "pairs", "at",
      "amortized", "constant", "average", "cost", "per", "operation", "in",
      "many", "situations", "hash", "tables", "turn", "out", "to", "be",
      "more", "efficient", "than", "search", "trees", "or", "any", "other",
      "table", "lookup", "structure", "for", "this", "reason", "they", "are",
      "widely", "used", "in", "many", "kinds", "of", "computer", "software",
      "particularly", "for", "associative", "arrays", "database", "indexing",
      "caches", "and", "sets",

    "hashing",
      "the", "idea", "of", "hashing", "is", "to", "distribute", "the",
      "entries", "key", "value", "pairs", "across", "an", "array", "of",
      "buckets", "given", "a", "key", "the", "algorithm", "computes", "an",
      "index", "that", "suggests", "where", "the", "entry", "can", "be",
      "found", "index", "f", "key", "array", "size", "often", "this", "is",
      "done", "in", "two", "steps", "hash", "hashfunc", "key", "index", "hash",
      "array", "size", "in", "this", "method", "the", "hash", "is",
      "independent", "of", "the", "array", "size", "and", "it", "is", "then",
      "reduced", "to", "an", "index", "a", "number", "between", "and", "array",
      "size", "using", "the", "modulus", "operator", "in", "the", "case",
      "that", "the", "array", "size", "is", "a", "power", "of", "two", "the",
      "remainder", "operation", "is", "reduced", "to", "masking", "which",
      "improves", "speed", "but", "can", "increase", "problems", "with", "a",
      "poor", "hash", "function",

    "choosing", "a", "good", "hash", "function",
      "a", "good", "hash", "function", "and", "implementation", "algorithm",
      "are", "essential", "for", "good", "hash", "table", "performance", "but",
      "may", "be", "difficult", "to", "achieve", "a", "basic", "requirement",
      "is", "that", "the", "function", "should", "provide", "a", "uniform",
      "distribution", "of", "hash", "values", "a", "non", "uniform",
      "distribution", "increases", "the", "number", "of", "collisions", "and",
      "the", "cost", "of", "resolving", "them", "uniformity", "is",
      "sometimes", "difficult", "to", "ensure", "by", "design", "but", "may",
      "be", "evaluated", "empirically", "using", "statistical", "tests", "e",
      "g", "a", "pearson", "s", "chi", "squared", "test", "for", "discrete",
      "uniform", "distributions", "the", "distribution", "needs", "to", "be",
      "uniform", "only", "for", "table", "sizes", "that", "occur", "in", "the",
      "application", "in", "particular", "if", "one", "uses", "dynamic",
      "resizing", "with", "exact", "doubling", "and", "halving", "of", "the",
      "table", "size", "s", "then", "the", "hash", "function", "needs", "to",
      "be", "uniform", "only", "when", "s", "is", "a", "power", "of", "two",
      "on", "the", "other", "hand", "some", "hashing", "algorithms", "provide",
      "uniform", "hashes", "only", "when", "s", "is", "a", "prime", "number",
      "for", "open", "addressing", "schemes", "the", "hash", "function",
      "should", "also", "avoid", "clustering", "the", "mapping", "of", "two",
      "or", "more", "keys", "to", "consecutive", "slots", "such", "clustering",
      "may", "cause", "the", "lookup", "cost", "to", "skyrocket", "even", "if",
      "the", "load", "factor", "is", "low", "and", "collisions", "are",
      "infrequent", "the", "popular", "multiplicative", "hash", "3", "is",
      "claimed", "to", "have", "particularly", "poor", "clustering",
      "behavior", "cryptographic", "hash", "functions", "are", "believed",
      "to", "provide", "good", "hash", "functions", "for", "any", "table",
      "size", "s", "either", "by", "modulo", "reduction", "or", "by", "bit",
      "masking", "they", "may", "also", "be", "appropriate", "if", "there",
      "is", "a", "risk", "of", "malicious", "users", "trying", "to",
      "sabotage", "a", "network", "service", "by", "submitting", "requests",
      "designed", "to", "generate", "a", "large", "number", "of", "collisions",
      "in", "the", "server", "s", "hash", "tables", "however", "the", "risk",
      "of", "sabotage", "can", "also", "be", "avoided", "by", "cheaper",
      "methods", "such", "as", "applying", "a", "secret", "salt", "to", "the",
      "data", "or", "using", "a", "universal", "hash", "function",

    "perfect", "hash", "function",
      "if", "all", "keys", "are", "known", "ahead", "of", "time", "a",
      "perfect", "hash", "function", "can", "be", "used", "to", "create", "a",
      "perfect", "hash", "table", "that", "has", "no", "collisions", "if",
      "minimal", "perfect", "hashing", "is", "used", "every", "location", "in",
      "the", "hash", "table", "can", "be", "used", "as", "well", "perfect",
      "hashing", "allows", "for", "constant", "time", "lookups", "in", "the",
      "worst", "case", "this", "is", "in", "contrast", "to", "most",
      "chaining", "and", "open", "addressing", "methods", "where", "the",
      "time", "for", "lookup", "is", "low", "on", "average", "but", "may",
      "be", "very", "large", "proportional", "to", "the", "number", "of",
      "entries", "for", "some", "sets", "of", "keys"
  ]

// Fill the dictionary with words from the first half of the text
let half: Dictionary<String, Bool> = {
  var dict: Dictionary<String, Bool> = [:]
  for i in 0 ..< text.count/2 {
    let word = text[i]
    dict[word] = true
  }
  return dict
}()

@inline(never)
public func run_Dictionary(n: Int) {
  var dict: Dictionary<String, Bool> = [:]

  // Check performance of filling the dictionary:
  for _ in 1...n {
    dict = [:]
    for word in text {
      dict[word] = true
    }
  }
  check(dict.count == 270)

  // Check performance of searching in the dictionary:
  dict = half
  // Count number of words from the first half in the entire text
  var count = 0
  for _ in 1...n {
    for word in text {
      if dict[word] != nil {
        count += 1
      }
    }
  }
  check(count == n*541)
}

class Box<T : Hashable> : Hashable {
  var value: T

  init(_ v: T) {
    value = v
  }

  func hash(into hasher: inout Hasher) {
    hasher.combine(value)
  }

  static func ==(lhs: Box, rhs: Box) -> Bool {
    return lhs.value == rhs.value
  }
}

// Fill the dictionary with words from the first half of the text
let halfObjects: Dictionary<Box<String>, Box<Bool>> = {
  var dict: Dictionary<Box<String>, Box<Bool>> = [:]
  for i in 0 ..< text.count/2 {
    let word = text[i]
    dict[Box(word)] = Box(true)
  }
  return dict
}()

@inline(never)
public func run_DictionaryOfObjects(n: Int) {
  var dict: Dictionary<Box<String>, Box<Bool>> = [:]

  // Check performance of filling the dictionary:
  for _ in 1...n {
    dict = [:]
    for word in text {
      dict[Box(word)] = Box(true)
    }
  }
  check(dict.count == 270)

  // Check performance of searching in the dictionary:
  dict = halfObjects
  // Count number of words from the first half in the entire text
  var count = 0
  for _ in 1...n {
    for word in text {
      if dict[Box(word)] != nil {
        count += 1
      }
    }
  }
  check(count == n*541)
}