1、RSHash
unsigned int RSHash(const std::string& str)
{
unsigned int b = 378551;
unsigned int a = 63689;
unsigned int hash = 0;
for(std::size_t i = 0; i < str.length(); i++)
{
hash = hash * a + str[i];
a = a * b;
}
return hash;
}
2、JSHash
unsigned int JSHash(const std::string& str)
{
unsigned int hash = 1315423911;
for(std::size_t i = 0; i < str.length(); i++)
{
hash ^= ((hash << 5) + str[i] + (hash >> 2));
}
return hash;
}
3、PJWHash
unsigned int PJWHash(const std::string& str)
{
unsigned int BitsInUnsignedInt = (unsigned int)(sizeof(unsigned int) * 8);
unsigned int ThreeQuarters = (unsigned int)((BitsInUnsignedInt * 3) / 4);
unsigned int OneEighth = (unsigned int)(BitsInUnsignedInt / 8);
unsigned int HighBits = (unsigned int)(0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth);
unsigned int hash = 0;
unsigned int test = 0;
for(std::size_t i = 0; i < str.length(); i++)
{
hash = (hash << OneEighth) + str[i];
if((test = hash & HighBits) != 0)
{
hash = (( hash ^ (test >> ThreeQuarters)) & (~HighBits));
}
}
return hash;
}
4、ELFHash
unsigned int ELFHash(const std::string& str)
{
unsigned int hash = 0;
unsigned int x = 0;
for(std::size_t i = 0; i < str.length(); i++)
{
hash = (hash << 4) + str[i];
if((x = hash & 0xF0000000L) != 0)
{
hash ^= (x >> 24);
}
hash &= ~x;
}
return hash;
}
5、BKDRHash
unsigned int BKDRHash(const std::string& str)
{
unsigned int seed = 131; // 31 131 1313 13131 131313 etc..
unsigned int hash = 0;
for(std::size_t i = 0; i < str.length(); i++)
{
hash = (hash * seed) + str[i];
}
return hash;
}
6、SDBMHash
unsigned int SDBMHash(const std::string& str)
{
unsigned int hash = 0;
for(std::size_t i = 0; i < str.length(); i++)
{
hash = str[i] + (hash << 6) + (hash << 16) - hash;
}
return hash;
}
7、DJBHash(times33)-这个用得非常多，很多库都用它。
unsigned int DJBHash(const std::string& str)
{
unsigned int hash = 5381;
for(std::size_t i = 0; i < str.length(); i++)
{
hash = ((hash << 5) + hash) + str[i];
}
return hash;
}
8、DEKHash
unsigned int DEKHash(const std::string& str)
{
unsigned int hash = static_cast(str.length());
for(std::size_t i = 0; i < str.length(); i++)
{
hash = ((hash << 5) ^ (hash >> 27)) ^ str[i];
}
return hash;
}
9、BPHash
unsigned int BPHash(const std::string& str)
{
unsigned int hash = 0;
for(std::size_t i = 0; i < str.length(); i++)
{
hash = hash << 7 ^ str[i];
}
return hash;
}
10、FNVHash
unsigned int FNVHash(const std::string& str)
{
const unsigned int fnv_prime = 0x811C9DC5;
unsigned int hash = 0;
for(std::size_t i = 0; i < str.length(); i++)
{
hash *= fnv_prime;
hash ^= str[i];
}
return hash;
}
11、APHash
unsigned int APHash(const std::string& str)
{
unsigned int hash = 0xAAAAAAAA;
for(std::size_t i = 0; i < str.length(); i++)
{
hash ^= ((i & 1) == 0) ? ( (hash << 7) ^ str[i] * (hash >> 3)) :
(~((hash << 11) + (str[i] ^ (hash >> 5))));
}
return hash;
}
12、MurmurHash - 非常新的一个哈希算法，应该是目前效率最高的一个哈希算法，使用率很高。(伪代码来自*）
Murmur2(key, len, seed)
m <- 0x5bd1e995
r <- 24
seed 0x9747b28c
hash <- seed XOR len
for each fourByteChunk of key
k <- fourByteChunk
k <- k * m
k <- k XOR (k >> r)
k <- k * m
hash <- hash * m
hash <- hash XOR k
with any remainingBytesInKey
remainingBytes SwapEndianOrderOf(remainingBytesInKey)
hash <- hash XOR remainingBytes
hash <- hash * m
hash <- hash XOR (hash >> 13)
hash <- hash * m
hash <- hash XOR (hash >> 15)
MurmurHash算法：高运算性能，低碰撞率，由Austin Appleby创建于2008年，现已应用到Hadoop、libstdc++、nginx、libmemcached等开源系统。2011年Appleby被Google雇佣，随后Google推出其变种的CityHash算法。
官方网站：https://sites.google.com/site/murmurhash/
MurmurHash算法，自称超级快的hash算法，是FNV的4-5倍。官方数据如下：
OneAtATime – 354.163715 mb/sec
FNV – 443.668038 mb/sec
SuperFastHash – 985.335173 mb/sec
lookup3 – 988.080652 mb/sec
MurmurHash 1.0 – 1363.293480 mb/sec
MurmurHash 2.0 – 2056.885653 mb/sec
但也有文章声称，只有当key的长度大于10字节的时候，MurmurHash的运算速度才快于DJB。“从计算速度上来看，MurmurHash只适用于已知长度的、长度比较长的字符”。