88.字符串哈希表返数字

常用字符串哈希函数有 BKDRHash，APHash，DJBHash，JSHash，RSHash，SDBMHash，PJWHash，ELFHash等等。对于以上几种哈希函数，我对其进行了一个小小的评测。

 1 // BKDR Hash Function
 2 unsigned int BKDRHash(char *str)
 3 {
 4     unsigned int seed = 131; // 31 131 1313 13131 131313 etc..
 5     unsigned int hash = 0;
 6  
 7     while (*str)
 8     {
 9         hash = hash * seed + (*str++);
10     }
11  
12     return (hash & 0x7FFFFFFF);
13 }

 1 unsigned int SDBMHash(char *str)
 2 {
 3     unsigned int hash = 0;
 4  
 5     while (*str)
 6     {
 7         // equivalent to: hash = 65599*hash + (*str++);
 8         hash = (*str++) + (hash << 6) + (hash << 16) - hash;
 9     }
10  
11     return (hash & 0x7FFFFFFF);
12 }

  1 unsigned int SDBMHash(char *str)
  2 {
  3     unsigned int hash = 0;
  4  
  5     while (*str)
  6     {
  7         // equivalent to: hash = 65599*hash + (*str++);
  8         hash = (*str++) + (hash << 6) + (hash << 16) - hash;
  9     }
 10  
 11     return (hash & 0x7FFFFFFF);
 12 }
 13  
 14 // RS Hash Function
 15 unsigned int RSHash(char *str)
 16 {
 17     unsigned int b = 378551;
 18     unsigned int a = 63689;
 19     unsigned int hash = 0;
 20  
 21     while (*str)
 22     {
 23         hash = hash * a + (*str++);
 24         a *= b;
 25     }
 26  
 27     return (hash & 0x7FFFFFFF);
 28 }
 29  
 30 // JS Hash Function
 31 unsigned int JSHash(char *str)
 32 {
 33     unsigned int hash = 1315423911;
 34  
 35     while (*str)
 36     {
 37         hash ^= ((hash << 5) + (*str++) + (hash >> 2));
 38     }
 39  
 40     return (hash & 0x7FFFFFFF);
 41 }
 42  
 43 // P. J. Weinberger Hash Function
 44 unsigned int PJWHash(char *str)
 45 {
 46     unsigned int BitsInUnignedInt = (unsigned int)(sizeof(unsigned int) * 8);
 47     unsigned int ThreeQuarters    = (unsigned int)((BitsInUnignedInt  * 3) / 4);
 48     unsigned int OneEighth        = (unsigned int)(BitsInUnignedInt / 8);
 49     unsigned int HighBits         = (unsigned int)(0xFFFFFFFF) << (BitsInUnignedInt - OneEighth);
 50     unsigned int hash             = 0;
 51     unsigned int test             = 0;
 52  
 53     while (*str)
 54     {
 55         hash = (hash << OneEighth) + (*str++);
 56         if ((test = hash & HighBits) != 0)
 57         {
 58             hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));
 59         }
 60     }
 61  
 62     return (hash & 0x7FFFFFFF);
 63 }
 64  
 65 // ELF Hash Function
 66 unsigned int ELFHash(char *str)
 67 {
 68     unsigned int hash = 0;
 69     unsigned int x    = 0;
 70  
 71     while (*str)
 72     {
 73         hash = (hash << 4) + (*str++);
 74         if ((x = hash & 0xF0000000L) != 0)
 75         {
 76             hash ^= (x >> 24);
 77             hash &= ~x;
 78         }
 79     }
 80  
 81     return (hash & 0x7FFFFFFF);
 82 }
 83  
 84 // BKDR Hash Function
 85 unsigned int BKDRHash(char *str)
 86 {
 87     unsigned int seed = 131; // 31 131 1313 13131 131313 etc..
 88     unsigned int hash = 0;
 89  
 90     while (*str)
 91     {
 92         hash = hash * seed + (*str++);
 93     }
 94  
 95     return (hash & 0x7FFFFFFF);
 96 }
 97  
 98 // DJB Hash Function
 99 unsigned int DJBHash(char *str)
100 {
101     unsigned int hash = 5381;
102  
103     while (*str)
104     {
105         hash += (hash << 5) + (*str++);
106     }
107  
108     return (hash & 0x7FFFFFFF);
109 }
110  
111 // AP Hash Function
112 unsigned int APHash(char *str)
113 {
114     unsigned int hash = 0;
115     int i;
116  
117     for (i=0; *str; i++)
118     {
119         if ((i & 1) == 0)
120         {
121             hash ^= ((hash << 7) ^ (*str++) ^ (hash >> 3));
122         }
123         else
124         {
125             hash ^= (~((hash << 11) ^ (*str++) ^ (hash >> 5)));
126         }
127     }
128  
129     return (hash & 0x7FFFFFFF);
130 }

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原文地址：https://www.cnblogs.com/xiaochi/p/8458626.html