值類型和引用類型在hashtable里面性能比較分析1 -GetHashCode()
上篇文章中，測試了一下值類型數據和引用類型數據在hashtable中插入和讀取的性能，測試結果和本人預期也有一些出入，msdn有一篇文章介紹在box,unbox的時候，性能關系為:class>interface>int,原文：Open the Box! Quick，進一步分析了上篇測試，發現其實影響測試性能還有其它幾個方面的因素，本篇就針對不同數據類型在GetHashCode()上面的消耗
測試程序如下;
結果表，我暫且不畫在這上面了，因為比較多，而且不好排版，我只說一下結果，int類型的數據比字符串類型的在GetHashCode()的效率上要高50多倍,比Class的也高50-70倍
察看了GetHashCode()的實現
Int32
而object的實現方法，我 不太理解：
測試程序如下;
1
System.Diagnostics.Stopwatch stopWatch = new System.Diagnostics.Stopwatch();
2 stopWatch.Start();
3 for (int i = 0; i < CompareCount; i++)
4
{
5
int hashCode = i.GetHashCode();
6
}
7 stopWatch.Stop();
8 System.Diagnostics.Stopwatch stopWatch2 = new System.Diagnostics.Stopwatch();
9 stopWatch2.Start();
10 for (int i = 0; i < CompareCount; i++)
11 {
12 int hashCode = i.ToString().GetHashCode();
13 }
14 stopWatch2.Stop();
15 System.Diagnostics.Stopwatch stopWatch3 = new System.Diagnostics.Stopwatch();
16 stopWatch3.Start();
17 for (int i = 0; i < CompareCount; i++)
18 {
19 int hashCode = new Test().GetHashCode();
20 }
21 stopWatch3.Stop();
22 long t1 = stopWatch.ElapsedTicks;
23 long t2 = stopWatch2.ElapsedTicks;
24 long t3 = stopWatch3.ElapsedTicks;
25 Console.WriteLine(t1.ToString());
26 Console.WriteLine(t2.ToString());
27 Console.WriteLine(t3.ToString());
28 Console.WriteLine((double)(t2/t1));
29 ArrayList list = new ArrayList();
30 }
System.Diagnostics.Stopwatch stopWatch = new System.Diagnostics.Stopwatch();2
stopWatch.Start();3
for (int i = 0; i < CompareCount; i++)4
{
5
int hashCode = i.GetHashCode();6
}7
stopWatch.Stop();8
System.Diagnostics.Stopwatch stopWatch2 = new System.Diagnostics.Stopwatch();9
stopWatch2.Start();10
for (int i = 0; i < CompareCount; i++)11
{12
int hashCode = i.ToString().GetHashCode();13
}14
stopWatch2.Stop();15
System.Diagnostics.Stopwatch stopWatch3 = new System.Diagnostics.Stopwatch();16
stopWatch3.Start();17
for (int i = 0; i < CompareCount; i++)18
{19
int hashCode = new Test().GetHashCode();20
}21
stopWatch3.Stop();22
long t1 = stopWatch.ElapsedTicks;23
long t2 = stopWatch2.ElapsedTicks;24
long t3 = stopWatch3.ElapsedTicks;25
Console.WriteLine(t1.ToString());26
Console.WriteLine(t2.ToString());27
Console.WriteLine(t3.ToString());28
Console.WriteLine((double)(t2/t1));29
ArrayList list = new ArrayList();30
}結果表，我暫且不畫在這上面了，因為比較多，而且不好排版，我只說一下結果，int類型的數據比字符串類型的在GetHashCode()的效率上要高50多倍,比Class的也高50-70倍
察看了GetHashCode()的實現
Int32
1public override int GetHashCode()
2{
3 return this;
4}
5
6
public override int GetHashCode()2
{3
return this;4
}5
6
String
1[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
2public override unsafe int GetHashCode()
3{
4 fixed (char* text1 = ((char*) this))
5
{
6 char* chPtr1 = text1;
7 int num1 = 0x15051505;
8 int num2 = num1;
9 int* numPtr1 = (int*) chPtr1;
10 for (int num3 = this.Length; num3 > 0; num3 -= 4)
11 {
12 num1 = (((num1 << 5) + num1) + (num1 >> 0x1b)) ^ numPtr1[0];
13 if (num3 <= 2)
14 {
15 break;
16
}
17 num2 = (((num2 << 5) + num2) + (num2 >> 0x1b)) ^ numPtr1[1];
18 numPtr1 += 2;
19 }
20 return (num1 + (num2 * 0x5d588b65));
21 }
22}
23
24
25
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]2
public override unsafe int GetHashCode()3
{4
fixed (char* text1 = ((char*) this))5
{
6
char* chPtr1 = text1;7
int num1 = 0x15051505;8
int num2 = num1;9
int* numPtr1 = (int*) chPtr1;10
for (int num3 = this.Length; num3 > 0; num3 -= 4)11
{12
num1 = (((num1 << 5) + num1) + (num1 >> 0x1b)) ^ numPtr1[0];13
if (num3 <= 2)14
{15
break;16
}17
num2 = (((num2 << 5) + num2) + (num2 >> 0x1b)) ^ numPtr1[1];18
numPtr1 += 2;19
}20
return (num1 + (num2 * 0x5d588b65));21
}22
}23
24
25
而object的實現方法，我 不太理解：
1public virtual int GetHashCode()
2{
3 return object.InternalGetHashCode(this);
4}
5
6
7[MethodImpl(MethodImplOptions.InternalCall)]
8internal static extern int InternalGetHashCode(object obj);
9
public virtual int GetHashCode()2
{3
return object.InternalGetHashCode(this);4
}5
6
7
[MethodImpl(MethodImplOptions.InternalCall)]8
internal static extern int InternalGetHashCode(object obj);9
object的具體處理方法
而從int,string類型算法可以輕易看出效率差別，雖然string類型還有unsafe .
而且，值類型必須重寫GetHashCode。
從這里可以看出，在上次測試中，GetHashCode幫了int類型不少忙呀！
作者：jillzhang
出處：http://jillzhang.cnblogs.com/
本文版權歸作者和博客園共有，歡迎轉載，但未經作者同意必須保留此段聲明，且在文章頁面明顯位置給出原文連接，否則保留追究法律責任的權利。
出處：http://jillzhang.cnblogs.com/
本文版權歸作者和博客園共有，歡迎轉載，但未經作者同意必須保留此段聲明，且在文章頁面明顯位置給出原文連接，否則保留追究法律責任的權利。
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