关于HashCode做key的可能性

        // Gets a hash code for this string.  If strings A and B are such that A.Equals(B), then 
        // they will return the same hash code.
        [System.Security.SecuritySafeCritical]  // auto-generated 
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)] 
        public override int GetHashCode() {
            unsafe { 
                fixed (char *src = this) {
                    Contract.Assert(src[this.Length] == '\0', "src[this.Length] == '\\0'");
                    Contract.Assert( ((int)src)%4 == 0, "Managed string should start at 4 bytes boundary");
 
#if WIN32
                    int hash1 = (5381<<16) + 5381; 
#else 
                    int hash1 = 5381;
#endif 
                    int hash2 = hash1;

#if WIN32
                    // 32bit machines. 
                    int* pint = (int *)src;
                    int len = this.Length; 
                    while(len > 0) { 
                        hash1 = ((hash1 <<5) + hash1 + (hash1 >> 27)) ^ pint[0];
                        if( len <= 2) { 
                            break;
                        }
                        hash2 = ((hash2 <<5) + hash2 + (hash2 >> 27)) ^ pint[1];
                        pint += 2; 
                        len  -= 4;
                    } 
#else 
                    int     c;
                    char *s = src; 
                    while ((c = s[0]) != 0) {
                        hash1 = ((hash1 <<5) + hash1) ^ c;
                        c = s[1];
                        if (c == 0) 
                            break;
                        hash2 = ((hash2 <<5) + hash2) ^ c; 
                        s += 2; 
                    }
#endif 
#if DEBUG
                    // We want to ensure we can change our hash function daily.
                    // This is perfectly fine as long as you don't persist the
                    // value from GetHashCode to disk or count on String A 
                    // hashing before string B.  Those are bugs in your code.
                    hash1 ^= ThisAssembly.DailyBuildNumber; 
#endif 
                    return hash1 + (hash2 * 1566083941);
                } 
            }
        }