几个hash算法的实现

1）几种经典的Hash算法的实现(源代码)
URL：http://blog.minidx.com/2008/01/27/446.html

ByMinidxer| January 27, 2008

哈希算法将任意长度的二进制值映射为固定长度的较小二进制值，这个小的二进制值称为哈希值。哈希值是一段数据唯一且极其紧凑的数值表示形式。如果散列一段 明文而且哪怕只更改该段落的一个字母，随后的哈希都将产生不同的值。要找到散列为同一个值的两个不同的输入，在计算上是不可能的，所以数据的哈希值可以检 验数据的完整性。

 

链表查找的时间效率为O(N)，二分法为log2N，B+ Tree为log2N，但Hash链表查找的时间效率为O(1)。

设计高效算法往往需要使用Hash链表，常数级的查找速度是任何别的算法无法比拟的，Hash链表的构造和冲突的不同实现方法对效率当然有一定的影 响，然 而Hash函数是Hash链表最核心的部分，下面是几款经典软件中使用到的字符串Hash函数实现，通过阅读这些代码，我们可以在Hash算法的执行效 率、离散性、空间利用率等方面有比较深刻的了解。

下面分别介绍几个经典软件中出现的字符串Hash函数。

●PHP中出现的字符串Hash函数

staticunsignedlonghashpjw(char*arKey, unsignedintnKeyLength){unsignedlongh = 0, g;char*arEnd=arKey+nKeyLength;while(arKey < arEnd) {h = (h << 4) + *arKey++;if((g = (h & 0xF0000000))) {h = h ^ (g >> 24);h = h ^ g;}}returnh;}

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●OpenSSL中出现的字符串Hash函数

unsignedlonglh_strhash(char*str){inti,l;unsignedlongret=0;unsignedshort*s;if(str == NULL)return(0);l=(strlen(str)+1)/2;s=(unsignedshort*)str;for(i=0; iret^=(s[i]<<(i&0×0f));return(ret);}/* The following hash seems to work very well on normal text strings* no collisions on /usr/dict/words and it distributes on %2^n quite* well, not as good as MD5, but still good.*/unsignedlonglh_strhash(constchar*c){unsignedlongret=0;longn;unsignedlongv;intr;if((c == NULL) || (*c ==‘/0′))return(ret);/*unsigned char b[16];MD5(c,strlen(c),b);return(b[0]|(b[1]<<8)|(b[2]<<16)|(b[3]<<24));*/n=0×100;while(*c){v=n|(*c);n+=0×100;r= (int)((v>>2)^v)&0×0f;ret=(ret(32-r));ret&=0xFFFFFFFFL;ret^=v*v;c++;}return((ret>>16)^ret);}

●MySql中出现的字符串Hash函数

#ifndef NEW_HASH_FUNCTION/* Calc hashvalue for a key */staticuintcalc_hashnr(constbyte*key,uintlength){registeruintnr=1, nr2=4;while(length–){nr^= (((nr & 63)+nr2)*((uint) (uchar) *key++))+ (nr << 8);nr2+=3;}return((uint) nr);}/* Calc hashvalue for a key, case indepenently */staticuintcalc_hashnr_caseup(constbyte*key,uintlength){registeruintnr=1, nr2=4;while(length–){nr^= (((nr & 63)+nr2)*((uint) (uchar) toupper(*key++)))+ (nr << 8);nr2+=3;}return((uint) nr);}#else/** Fowler/Noll/Vo hash** The basis of the hash algorithm was taken from an idea sent by email to the* IEEE Posix P1003.2 mailing list from Phong Vo ([e-mail]) and* Glenn Fowler ([e-mail]). Landon Curt Noll ([e-mail])* later improved on their algorithm.** The magic is in the interesting relationship between the special prime* 16777619 (2^24 + 403) and 2^32 and 2^8.** This hash produces the fewest collisions of any function that we’ve seen so* far, and works well on both numbers and strings.*/uintcalc_hashnr(constbyte*key,uintlen){constbyte*end=key+len;uinthash;for(hash = 0; key < end; key++){hash *= 16777619;hash ^= (uint) *(uchar*) key;}return(hash);}uintcalc_hashnr_caseup(constbyte*key,uintlen){constbyte*end=key+len;uinthash;for(hash = 0; key < end; key++){hash *= 16777619;hash ^= (uint) (uchar) toupper(*key);}return(hash);}#endif

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Mysql中对字符串Hash函数还区分了大小写

●另一个经典字符串Hash函数

unsignedinthash(char*str){register unsignedinth;register unsignedchar*p;for(h=0, p = (unsignedchar*)str; *p ; p++)h = 31 * h + *p;returnh;}

2）大量HASH算法的实现
URL：http://hi.baidu.com/algorithms/blog/item/79caabee879ece2a2cf53440.html

Hash算法有很多很多种类。具体的可以参考之前我写的Hash算法的一些分析。本处给大家提供一个集合了很多使用的Hash算法的类，应该可以满足不少人的需要的：

/**
* Hash算法大全<br>
* 推荐使用FNV1算法
* @algorithm None
* @author Goodzzp 2006-11-20
* @lastEdit Goodzzp 2006-11-20
* @editDetail Create
*/
public class HashAlgorithms
{
/**
* 加法hash
* @param key 字符串
* @param prime 一个质数
* @return hash结果
*/
public static int additiveHash(String key, int prime)
{
   int hash, i;
   for (hash = key.length(), i = 0; i < key.length(); i++)
    hash += key.charAt(i);
   return (hash % prime);
}

/**
* 旋转hash
* @param key 输入字符串
* @param prime 质数
* @return hash值
*/
public static int rotatingHash(String key, int prime)
{
   int hash, i;
   for (hash=key.length(), i=0; i<key.length(); ++i)
     hash = (hash<<4)^(hash>>28)^key.charAt(i);
   return (hash % prime);
//   return (hash ^ (hash>>10) ^ (hash>>20));
}

// 替代：
// 使用：hash = (hash ^ (hash>>10) ^ (hash>>20)) & mask;
// 替代：hash %= prime;


/**
* MASK值，随便找一个值，最好是质数
*/
static int M_MASK = 0x8765fed1;
/**
* 一次一个hash
* @param key 输入字符串
* @return 输出hash值
*/
public static int oneByOneHash(String key)
{
   int   hash, i;
   for (hash=0, i=0; i<key.length(); ++i)
   {
     hash += key.charAt(i);
     hash += (hash << 10);
     hash ^= (hash >> 6);
   }
   hash += (hash << 3);
   hash ^= (hash >> 11);
   hash += (hash << 15);
//   return (hash & M_MASK);
   return hash;
}

/**
* Bernstein's hash
* @param key 输入字节数组
* @param level 初始hash常量
* @return 结果hash
*/
public static int bernstein(String key)
{
   int hash = 0;
   int i;
   for (i=0; i<key.length(); ++i) hash = 33*hash + key.charAt(i);
   return hash;
}

//
//// Pearson's Hash
// char pearson(char[]key, ub4 len, char tab[256])
// {
//   char hash;
//   ub4 i;
//   for (hash=len, i=0; i<len; ++i)
//     hash=tab[hash^key[i]];
//   return (hash);
// }

//// CRC Hashing，计算crc,具体代码见其他
// ub4 crc(char *key, ub4 len, ub4 mask, ub4 tab[256])
// {
//   ub4 hash, i;
//   for (hash=len, i=0; i<len; ++i)
//     hash = (hash >> 8) ^ tab[(hash & 0xff) ^ key[i]];
//   return (hash & mask);
// }

/**
* Universal Hashing
*/
public static int universal(char[]key, int mask, int[] tab)
{
   int hash = key.length, i, len = key.length;
   for (i=0; i<(len<<3); i+=8)
   {
     char k = key[i>>3];
     if ((k&0x01) == 0) hash ^= tab[i+0];
     if ((k&0x02) == 0) hash ^= tab[i+1];
     if ((k&0x04) == 0) hash ^= tab[i+2];
     if ((k&0x08) == 0) hash ^= tab[i+3];
     if ((k&0x10) == 0) hash ^= tab[i+4];
     if ((k&0x20) == 0) hash ^= tab[i+5];
     if ((k&0x40) == 0) hash ^= tab[i+6];
     if ((k&0x80) == 0) hash ^= tab[i+7];
   }
   return (hash & mask);
}

/**
* Zobrist Hashing
*/
public static int zobrist( char[] key,int mask, int[][] tab)
{
   int hash, i;
   for (hash=key.length, i=0; i<key.length; ++i)
     hash ^= tab[i][key[i]];
   return (hash & mask);
}

// LOOKUP3
// 见Bob Jenkins(3).c文件

// 32位FNV算法
static int M_SHIFT = 0;
/**
* 32位的FNV算法
* @param data 数组
* @return int值
*/
    public static int FNVHash(byte[] data)
    {
        int hash = (int)2166136261L;
        for(byte b : data)
            hash = (hash * 16777619) ^ b;
        if (M_SHIFT == 0)
            return hash;
        return (hash ^ (hash >> M_SHIFT)) & M_MASK;
    }
    /**
     * 改进的32位FNV算法1
     * @param data 数组
     * @return int值
     */
    public static int FNVHash1(byte[] data)
    {
        final int p = 16777619;
        int hash = (int)2166136261L;
        for(byte b:data)
            hash = (hash ^ b) * p;
        hash += hash << 13;
        hash ^= hash >> 7;
        hash += hash << 3;
        hash ^= hash >> 17;
        hash += hash << 5;
        return hash;
    }
    /**
     * 改进的32位FNV算法1
     * @param data 字符串
     * @return int值
     */
    public static int FNVHash1(String data)
    {
        final int p = 16777619;
        int hash = (int)2166136261L;
        for(int i=0;i<data.length();i++)
            hash = (hash ^ data.charAt(i)) * p;
        hash += hash << 13;
        hash ^= hash >> 7;
        hash += hash << 3;
        hash ^= hash >> 17;
        hash += hash << 5;
        return hash;
    }

    /**
     * Thomas Wang的算法，整数hash
     */
    public static int intHash(int key)
    {
      key += ~(key << 15);
      key ^= (key >>> 10);
      key += (key << 3);
      key ^= (key >>> 6);
      key += ~(key << 11);
      key ^= (key >>> 16);
      return key;
    }
    /**
     * RS算法hash
     * @param str 字符串
     */
    public static int RSHash(String str)
    {
        int b    = 378551;
        int a    = 63689;
        int hash = 0;

       for(int i = 0; i < str.length(); i++)
       {
          hash = hash * a + str.charAt(i);
          a    = a * b;
       }

       return (hash & 0x7FFFFFFF);
    }
    /* End Of RS Hash Function */

    /**
     * JS算法
     */
    public static int JSHash(String str)
    {
       int hash = 1315423911;

       for(int i = 0; i < str.length(); i++)
       {
          hash ^= ((hash << 5) + str.charAt(i) + (hash >> 2));
       }

       return (hash & 0x7FFFFFFF);
    }
    /* End Of JS Hash Function */

    /**
     * PJW算法
     */
    public static int PJWHash(String str)
    {
        int BitsInUnsignedInt = 32;
        int ThreeQuarters     = (BitsInUnsignedInt * 3) / 4;
        int OneEighth         = BitsInUnsignedInt / 8;
        int HighBits          = 0xFFFFFFFF << (BitsInUnsignedInt - OneEighth);
        int hash              = 0;
        int 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 & 0x7FFFFFFF);
    }
    /* End Of P. J. Weinberger Hash Function */

    /**
     * ELF算法
     */
    public static int ELFHash(String str)
    {
        int hash = 0;
        int x    = 0;

       for(int i = 0; i < str.length(); i++)
       {
          hash = (hash << 4) + str.charAt(i);
          if((x = (int)(hash & 0xF0000000L)) != 0)
          {
             hash ^= (x >> 24);
             hash &= ~x;
          }
       }

       return (hash & 0x7FFFFFFF);
    }
    /* End Of ELF Hash Function */

    /**
     * BKDR算法
     */
    public static int BKDRHash(String str)
    {
        int seed = 131; // 31 131 1313 13131 131313 etc..
        int hash = 0;

       for(int i = 0; i < str.length(); i++)
       {
          hash = (hash * seed) + str.charAt(i);
       }

       return (hash & 0x7FFFFFFF);
    }
    /* End Of BKDR Hash Function */

    /**
     * SDBM算法
     */
    public static int SDBMHash(String str)
    {
        int hash = 0;

       for(int i = 0; i < str.length(); i++)
       {
          hash = str.charAt(i) + (hash << 6) + (hash << 16) - hash;
       }

       return (hash & 0x7FFFFFFF);
    }
    /* End Of SDBM Hash Function */

    /**
     * DJB算法
     */
    public static int DJBHash(String str)
    {
       int hash = 5381;

       for(int i = 0; i < str.length(); i++)
       {
          hash = ((hash << 5) + hash) + str.charAt(i);
       }

       return (hash & 0x7FFFFFFF);
    }
    /* End Of DJB Hash Function */

    /**
     * DEK算法
     */
    public static int DEKHash(String str)
    {
        int hash = str.length();

       for(int i = 0; i < str.length(); i++)
       {
          hash = ((hash << 5) ^ (hash >> 27)) ^ str.charAt(i);
       }

       return (hash & 0x7FFFFFFF);
    }
    /* End Of DEK Hash Function */

    /**
     * AP算法
     */
    public static int APHash(String str)
    {
        int hash = 0;

       for(int i = 0; i < str.length(); i++)
       {
          hash ^= ((i & 1) == 0) ? ( (hash << 7) ^ str.charAt(i) ^ (hash >> 3)) :
                                   (~((hash << 11) ^ str.charAt(i) ^ (hash >> 5)));
       }

//       return (hash & 0x7FFFFFFF);
       return hash;
    }
    /* End Of AP Hash Function */
   
    /**
     * JAVA自己带的算法
     */
    public static int java(String str)
{
   int h = 0;
   int ff = 0;
   int len = str.length();
   for (int i = 0; i < len; i++)
   {
    h = 31 * h + str.charAt(off++);
   }
   return h;
}
   
    /**
     * 混合hash算法，输出64位的值
     */
    public static long mixHash(String str)
    {
    long hash = str.hashCode();
    hash <<= 32;
    hash |= FNVHash1(str);
    return hash;
    }
}

3）WIKI
http://en.wikipedia.org/wiki/Cryptographic_hash_function

4）BOOST
http://www.boost.org/doc/libs/1_36_0/doc/html/hash.html