benchmark/single-source/RomanNumbers.swift

//===--- RomanNumbers.swift -----------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2018 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

//
// Mini benchmark implementing roman numeral conversions to/from integers.
// Measures performance of Substring.starts(with:) and String.append(),
// with very short string arguments.
//

public let RomanNumbers = [
  BenchmarkInfo(
    name: "RomanNumbers",
    runFunction: run_RomanNumbers,
    tags: [.api, .String, .algorithm])
]

let romanTable: KeyValuePairs<String, Int> = [
  "M": 1000,
  "CM": 900,
  "D": 500,
  "CD": 400,
  "C": 100,
  "XC": 90,
  "L": 50,
  "XL": 40,
  "X": 10,
  "IX": 9,
  "V": 5,
  "IV": 4,
  "I": 1,
]

extension BinaryInteger {
  var romanNumeral: String {
    var result = ""
    var value = self
  outer:
    while value > 0 {
      var position = 0
      for (i, (key: s, value: v)) in romanTable[position...].enumerated() {
        if value >= v {
          result += s
          value -= Self(v)
          position = i
          continue outer
        }
      }
      fatalError("Unreachable")
    }
    return result
  }

  init?(romanNumeral: String) {
    self = 0
    var input = Substring(romanNumeral)
  outer:
    while !input.isEmpty {
      var position = 0
      for (i, (key: s, value: v)) in romanTable[position...].enumerated() {
        if input.starts(with: s) {
          self += Self(v)
          input = input.dropFirst(s.count)
          position = i
          continue outer
        }
      }
      return nil
    }
  }
}

@inline(never)
func checkRomanNumerals(upTo limit: Int) {
  for i in 0 ..< limit {
    CheckResults(Int(romanNumeral: identity(i.romanNumeral)) == i)
  }
}

@inline(never)
public func run_RomanNumbers(_ N: Int) {
  for _ in 0 ..< 10 * N {
    checkRomanNumerals(upTo: 1100)
  }
}