哈希算法将任意长度的二进制值映射为较短的固定长度的二进制值，这个小的二进制值称为哈希值。
哈希函数用途广泛，这个程序给出了绝大多数常用的哈希函数。源程序来自：哈希算法_百度百科。
程序员可以根据自己的需要取用这些代码。
需要注意的是，有可能string类的方法已经发生变化。实际使用以下程序的时候，写成str.charAt(i)编译通过不了，改为str.at(i)则编译通过。
另外，这个代码并不是优化的代码，对字符串处理没有使用字符指针，处理效率低。
源程序如下：
class GeneralHashFunctionLibrary
{/*RSHash*/public long RSHash(String str){int b = 378551;int a = 63689;long hash = 0;for(int i = 0; i < str.length(); i++){hash = hash * a + str.charAt(i);a = a * b;}return hash;}/*JSHash*/public long JSHash(String str){long hash = 1315423911;for(int i = 0; i < str.length(); i++)hash ^= ((hash << 5) + str.charAt(i) + (hash >> 2));return hash;}/*PJWHash*/public long PJWHash(String str){long BitsInUnsignedInt = (long)(4 * 8);long ThreeQuarters = (long)((BitsInUnsignedInt * 3) / 4);long OneEighth = (long)(BitsInUnsignedInt / 8);long HighBits = (long)(0xFFFFFFFF)<<(BitsInUnsignedInt-OneEighth);long hash = 0;long test = 0;for(int i = 0; i < str.length(); i++){hash = (hash << OneEighth) + str.charAt(i);if((test = hash & HighBits) != 0)hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));}return hash;}/*ELFHash*/public long ELFHash(String str){long hash = 0;long x = 0;for(int i = 0; i < str.length(); i++){hash = (hash << 4) + str.charAt(i);if(( x = hash & 0xF0000000L) != 0)hash ^= ( x >> 24);hash &= ~x;}return hash;}/*BKDRHash*/public long BKDRHash(String str){long seed = 131;//31131131313131131313etc..long hash = 0;for(int i = 0; i < str.length(); i++)hash = (hash * seed) + str.charAt(i);return hash;}/*SDBMHash*/public long SDBMHash(String str){long hash = 0;for(int i = 0; i < str.length(); i++)hash = str.charAt(i) + (hash << 6) + (hash << 16) - hash;return hash;}/*DJBHash*/public long DJBHash(String str){long hash = 5381;for(int i = 0; i < str.length(); i++)hash = ((hash << 5) + hash) + str.charAt(i);return hash;}/*DEKHash*/public long DEKHash(String str){long hash = str.length();for(int i = 0; i < str.length(); i++)hash = ((hash << 5) ^ (hash >> 27)) ^ str.charAt(i);return hash;}/*BPHash*/public long BPHash(String str){long hash=0;for(int i = 0;i < str.length(); i++)hash = hash << 7 ^ str.charAt(i);return hash;}/*FNVHash*/public long FNVHash(String str){long fnv_prime = 0x811C9DC5;long hash = 0;for(int i = 0; i < str.length(); i++) {hash *= fnv_prime;hash ^= str.charAt(i);}return hash;}/*APHash*/long APHash(String str){long hash = 0xAAAAAAAA;for(int i = 0; i < str.length(); i++){if((i & 1) == 0)hash ^=((hash << 7) ^ str.charAt(i) ^ (hash >> 3));elsehash ^= (~((hash << 11) ^ str.charAt(i) ^ (hash >> 5)));}return hash;}
}
