8个常用的字符串哈希函数

最有用的两个

unsigned long long hash; 
// hash使用unsigned long long，超过了unsigned long long就相当于取模
//常用1
1  SDBMHash
int SDBMHash(char *str)
{
    hash = 0;
    while (*str) hash = (*str++) + (hash << 6) + (hash << 16) - hash;
    return hash;
}
//常用2 
int BKDRHash(char *str)
{
    int seed = 131; 
    int hash = 0;
    while (*str) hash = hash * seed + (*str++);
    return hash;
}

常见的8个

const int MAXN = 1000003;

//常用 1
1  SDBMHash
unsigned int SDBMHash(char *str)
{
    unsigned int hash = 0;
    while (*str)
    {
        // equivalent to: hash = 65599*hash + (*str++);
        hash = (*str++) + (hash << 6) + (hash << 16) - hash;
    }
    return (hash & 0x7FFFFFFF)%MAXN;
}
 
2  RS Hash Function
unsigned int RSHash(char *str)
{
    unsigned int b = 378551;
    unsigned int a = 63689;
    unsigned int hash = 0;
 
    while (*str)
    {
        hash = hash * a + (*str++);
        a *= b;
    }
    return (hash & 0x7FFFFFFF)%MAXN;
}
 
3 JS Hash Function
unsigned int JSHash(char *str)
{
    unsigned int hash = 1315423911;
 
    while (*str)
    {
        hash ^= ((hash << 5) + (*str++) + (hash >> 2));
    }
    return (hash & 0x7FFFFFFF)%MAXN;
}
 
4 P. J. Weinberger Hash Function
unsigned int PJWHash(char *str)
{
    unsigned int BitsInUnignedInt = (unsigned int)(sizeof(unsigned int) * 8);
    unsigned int ThreeQuarters    = (unsigned int)((BitsInUnignedInt  * 3) / 4);
    unsigned int OneEighth        = (unsigned int)(BitsInUnignedInt / 8);
    unsigned int HighBits         = (unsigned int)(0xFFFFFFFF) << (BitsInUnignedInt - OneEighth);
    unsigned int hash             = 0;
    unsigned int test             = 0;
    while (*str)
    {
        hash = (hash << OneEighth) + (*str++);
        if ((test = hash & HighBits) != 0)
        {
            hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));
        }
    }
    return (hash & 0x7FFFFFFF)%MAXN;
}
 
5 ELF Hash Function
unsigned int ELFHash(char *str)
{
    unsigned int hash = 0;
    unsigned int x    = 0;
    while (*str)
    {
        hash = (hash << 4) + (*str++);
        if ((x = hash & 0xF0000000L) != 0)
        {
            hash ^= (x >> 24);
            hash &= ~x;
        }
    }
    return (hash & 0x7FFFFFFF)%MAXN;
}
 
//常用2 
6 BKDR Hash Function
unsigned int BKDRHash(char *str)
{
    unsigned int seed = 131; // 31 131 1313 13131 131313 etc..
    unsigned int hash = 0;
    while (*str)
    {
        hash = hash * seed + (*str++);
    }
    return (hash & 0x7FFFFFFF)%MAXN;
}
 
7 DJB Hash Function
unsigned int DJBHash(char *str)
{
    unsigned int hash = 5381;
    while (*str)
    {
        hash += (hash << 5) + (*str++);
    }
    return (hash & 0x7FFFFFFF)%MAXN;
}
 
8 AP Hash Function
unsigned int APHash(char *str)
{
    unsigned int hash = 0;
    int i;
    for (i=0; *str; i++)
    {
        if ((i & 1) == 0)
        {
            hash ^= ((hash << 7) ^ (*str++) ^ (hash >> 3));
        }
        else
        {
            hash ^= (~((hash << 11) ^ (*str++) ^ (hash >> 5)));
        }
    }
    return (hash & 0x7FFFFFFF)%MAXN;
}