Created
November 8, 2018 12:40
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要素の型がわかっている場合の配列ダウンキャスト
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using BenchmarkDotNet.Attributes; | |
using BenchmarkDotNet.Running; | |
using System.Runtime.CompilerServices; | |
public class ArrayDowncastBenchmark | |
{ | |
string[] _stringData = new string[] { "a", "ab", "abc", "abcd", "abcde", "abcdef", "abcdefg" }; | |
object[] _objectData = new string[] { "a", "ab", "abc", "abcd", "abcde", "abcdef", "abcdefg" }; | |
[Benchmark] | |
public int MemberwiseCast() | |
{ | |
// 要素ごとに (string)_data[i] なキャストが掛かる | |
var sum = 0; | |
foreach (string s in _objectData) | |
sum += s.Length; | |
return sum; | |
} | |
[Benchmark] | |
public int ArrayCast() | |
{ | |
// 最初に1回、配列自体のキャストが掛かる | |
var data = (string[])_objectData; | |
var sum = 0; | |
foreach (var s in data) | |
sum += s.Length; | |
return sum; | |
} | |
public struct Wrap<T> | |
{ | |
public T Value; | |
} | |
[Benchmark] | |
public int UnsafeStructCast() | |
{ | |
// 謎の最適化。 | |
// string 1個だけのフィールドを持つ構造体に無理やり変換して使う。 | |
// これで倍くらい速くなる。 | |
var data = Unsafe.As<object[], Wrap<string>[]>(ref _objectData); | |
var sum = 0; | |
foreach (var s in data) | |
sum += s.Value.Length; | |
return sum; | |
} | |
[Benchmark(Baseline = true)] | |
public int Static() | |
{ | |
// 比較対象として、元から string[] なものを列挙 | |
var sum = 0; | |
foreach (var s in _stringData) | |
sum += s.Length; | |
return sum; | |
} | |
} | |
public class Program | |
{ | |
static void Main() | |
{ | |
BenchmarkRunner.Run<ArrayDowncastBenchmark>(); | |
} | |
} |
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