C#中Equals 与== 的区别

 1       private unsafe static bool EqualsHelper(String strA, String strB)
 2         {
 3             Contract.Requires(strA != null);
 4             Contract.Requires(strB != null);
 5             Contract.Requires(strA.Length == strB.Length);
 6             //保存当前String长度
 7             int length = strA.Length;
 8             //固定住二个字符串的首字符地址
 9             fixed (char* ap = &strA.m_firstChar) fixed (char* bp = &strB.m_firstChar)
10             {
11                 //定义二个指针用来保存字符串首地址
12                 char* a = ap;
13                 char* b = bp;
14                 //下面判断是否是AMD64位系统，我这不是就往下执行
15                 // unroll the loop
16 #if AMD64
17                 // for AMD64 bit platform we unroll by 12 and
18                 // check 3 qword at a time. This is less code
19                 // than the 32 bit case and is shorter
20                 // pathlength
21 
22                 while (length >= 12)
23                 {
24                     if (*(long*)a     != *(long*)b) return false;
25                     if (*(long*)(a+4) != *(long*)(b+4)) return false;
26                     if (*(long*)(a+8) != *(long*)(b+8)) return false;
27                     a += 12; b += 12; length -= 12;
28                 }
29                 
30 #else           
31                 //A段感觉是多余的，直接执行B段就完事
32                 //判断字符串A长度是否大于10，为真的话每次读取四个字节进行比较
33                 //如果不相同就直接返回false,最后指针向后移动10个字节,长度减少10
34                 while (length >= 10)
35                 {
36                     if (*(int*)a != *(int*)b) return false;
37                     if (*(int*)(a+2) != *(int*)(b+2)) return false;
38                     if (*(int*)(a+4) != *(int*)(b+4)) return false;
39                     if (*(int*)(a+6) != *(int*)(b+6)) return false;
40                     if (*(int*)(a+8) != *(int*)(b+8)) return false;
41                     a += 10; b += 10; length -= 10;
42                 }
43 #endif
44 
45                 // This depends on the fact that the String objects are
46                 // always zero terminated and that the terminating zero is not included
47                 // in the length. For odd string sizes, the last compare will include
48                 // the zero terminator.
49 
50                 //B段
51                 //这里是前10个字节的匹配情况下，从+10开位置开始继续每四个字节的进行比较
52                 //只要不匹配，跳出循环，那长度肯定肯定不为0, 这里break也是多余，直接return false
53                 //如果所有字节都匹配，最终长度为0，跳出循环，返回真
54                 while (length > 0) 
55                 {
56                     if (*(int*)a != *(int*)b) break;
57                     a += 2; b += 2; length -= 2;
58                 }
59 
60                 return (length 0);
61             }
62         }