C/C++编程：实现hash函数

客官°小女子只卖身不卖艺 2022-09-04 11:44 59阅读 0赞

# hash函数的作用： #

> 目的：根据一个key生成生成一个数字。（一个key对应一个数字，不同的key具有不同的数字）  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70_pic_center]  
> 当hash冲突不严重的时候，查找某个键，只需要求hash值，然后取余，定位到数组的某个下标即可，时间复杂度为`O(1)`

当hash冲突十分严重的时候，每个数组元素对应的链表会越来越长，即使定位到数组的某个下标，也要遍历一条很长很长的链表，就退化为查找链表了。时间复杂度为`O(n)`

所以hash表实现要解决的问题就是寻找**相对均匀，具有很好的随机分布性**的hash函数。

*  具体请参考[golang之哈希表：散列查找算法][golang]

# 实现 #

//
    // Created by oceanstar on 2021/8/13.
    //
    
    #ifndef OCEANSTAR_HTTP_ACL_HASH_H
    #define OCEANSTAR_HTTP_ACL_HASH_H
    
    namespace oceanstar{
        
        # define	acl_uint64	unsigned long long int
        acl_uint64 acl_hash_crc64(const void *buf, size_t len);
    }
    #endif //OCEANSTAR_HTTP_ACL_HASH_H

//
    // Created by oceanstar on 2021/8/13.
    //
    #include <cstdio>
    #include "acl_hash.h"
    
    namespace oceanstar{
        
    
    #define INITIALCRC    0xffffffffffffffffll
    
    
        static unsigned long long int crc64_table[256] = {
        
                0x0ll,
                0x7ad870c830358979ll, 0xf5b0e190606b12f2ll, 0x8f689158505e9b8bll,
                0xc038e5739841b68fll, 0xbae095bba8743ff6ll, 0x358804e3f82aa47dll,
                0x4f50742bc81f2d04ll, 0xab28ecb46814fe75ll, 0xd1f09c7c5821770cll,
                0x5e980d24087fec87ll, 0x24407dec384a65fell, 0x6b1009c7f05548fall,
                0x11c8790fc060c183ll, 0x9ea0e857903e5a08ll, 0xe478989fa00bd371ll,
                0x7d08ff3b88be6f81ll, 0x7d08ff3b88be6f8ll, 0x88b81eabe8d57d73ll,
                0xf2606e63d8e0f40all, 0xbd301a4810ffd90ell, 0xc7e86a8020ca5077ll,
                0x4880fbd87094cbfcll, 0x32588b1040a14285ll, 0xd620138fe0aa91f4ll,
                0xacf86347d09f188dll, 0x2390f21f80c18306ll, 0x594882d7b0f40a7fll,
                0x1618f6fc78eb277bll, 0x6cc0863448deae02ll, 0xe3a8176c18803589ll,
                0x997067a428b5bcf0ll, 0xfa11fe77117cdf02ll, 0x80c98ebf2149567bll,
                0xfa11fe77117cdf0ll, 0x75796f2f41224489ll, 0x3a291b04893d698dll,
                0x40f16bccb908e0f4ll, 0xcf99fa94e9567b7fll, 0xb5418a5cd963f206ll,
                0x513912c379682177ll, 0x2be1620b495da80ell, 0xa489f35319033385ll,
                0xde51839b2936bafcll, 0x9101f7b0e12997f8ll, 0xebd98778d11c1e81ll,
                0x64b116208142850all, 0x1e6966e8b1770c73ll, 0x8719014c99c2b083ll,
                0xfdc17184a9f739fall, 0x72a9e0dcf9a9a271ll, 0x8719014c99c2b08ll,
                0x4721e43f0183060cll, 0x3df994f731b68f75ll, 0xb29105af61e814fell,
                0xc849756751dd9d87ll, 0x2c31edf8f1d64ef6ll, 0x56e99d30c1e3c78fll,
                0xd9810c6891bd5c04ll, 0xa3597ca0a188d57dll, 0xec09088b6997f879ll,
                0x96d1784359a27100ll, 0x19b9e91b09fcea8bll, 0x636199d339c963f2ll,
                0xdf7adabd7a6e2d6fll, 0xa5a2aa754a5ba416ll, 0x2aca3b2d1a053f9dll,
                0x50124be52a30b6e4ll, 0x1f423fcee22f9be0ll, 0x659a4f06d21a1299ll,
                0xeaf2de5e82448912ll, 0x902aae96b271006bll, 0x74523609127ad31all,
                0xe8a46c1224f5a63ll, 0x81e2d7997211c1e8ll, 0xfb3aa75142244891ll,
                0xb46ad37a8a3b6595ll, 0xceb2a3b2ba0eececll, 0x41da32eaea507767ll,
                0x3b024222da65fe1ell, 0xa2722586f2d042eell, 0xd8aa554ec2e5cb97ll,
                0x57c2c41692bb501cll, 0x2d1ab4dea28ed965ll, 0x624ac0f56a91f461ll,
                0x1892b03d5aa47d18ll, 0x97fa21650afae693ll, 0xed2251ad3acf6feall,
                0x95ac9329ac4bc9bll, 0x7382b9faaaf135e2ll, 0xfcea28a2faafae69ll,
                0x8632586aca9a2710ll, 0xc9622c4102850a14ll, 0xb3ba5c8932b0836dll,
                0x3cd2cdd162ee18e6ll, 0x460abd1952db919fll, 0x256b24ca6b12f26dll,
                0x5fb354025b277b14ll, 0xd0dbc55a0b79e09fll, 0xaa03b5923b4c69e6ll,
                0xe553c1b9f35344e2ll, 0x9f8bb171c366cd9bll, 0x10e3202993385610ll,
                0x6a3b50e1a30ddf69ll, 0x8e43c87e03060c18ll, 0xf49bb8b633338561ll,
                0x7bf329ee636d1eeall, 0x12b592653589793ll, 0x4e7b2d0d9b47ba97ll,
                0x34a35dc5ab7233eell, 0xbbcbcc9dfb2ca865ll, 0xc113bc55cb19211cll,
                0x5863dbf1e3ac9decll, 0x22bbab39d3991495ll, 0xadd33a6183c78f1ell,
                0xd70b4aa9b3f20667ll, 0x985b3e827bed2b63ll, 0xe2834e4a4bd8a21all,
                0x6debdf121b863991ll, 0x1733afda2bb3b0e8ll, 0xf34b37458bb86399ll,
                0x8993478dbb8deae0ll, 0x6fbd6d5ebd3716bll, 0x7c23a61ddbe6f812ll,
                0x3373d23613f9d516ll, 0x49aba2fe23cc5c6fll, 0xc6c333a67392c7e4ll,
                0xbc1b436e43a74e9dll, 0x95ac9329ac4bc9b5ll, 0xef74e3e19c7e40ccll,
                0x601c72b9cc20db47ll, 0x1ac40271fc15523ell, 0x5594765a340a7f3all,
                0x2f4c0692043ff643ll, 0xa02497ca54616dc8ll, 0xdafce7026454e4b1ll,
                0x3e847f9dc45f37c0ll, 0x445c0f55f46abeb9ll, 0xcb349e0da4342532ll,
                0xb1eceec59401ac4bll, 0xfebc9aee5c1e814fll, 0x8464ea266c2b0836ll,
                0xb0c7b7e3c7593bdll, 0x71d40bb60c401ac4ll, 0xe8a46c1224f5a634ll,
                0x927c1cda14c02f4dll, 0x1d148d82449eb4c6ll, 0x67ccfd4a74ab3dbfll,
                0x289c8961bcb410bbll, 0x5244f9a98c8199c2ll, 0xdd2c68f1dcdf0249ll,
                0xa7f41839ecea8b30ll, 0x438c80a64ce15841ll, 0x3954f06e7cd4d138ll,
                0xb63c61362c8a4ab3ll, 0xcce411fe1cbfc3call, 0x83b465d5d4a0eecell,
                0xf96c151de49567b7ll, 0x76048445b4cbfc3cll, 0xcdcf48d84fe7545ll,
                0x6fbd6d5ebd3716b7ll, 0x15651d968d029fcell, 0x9a0d8ccedd5c0445ll,
                0xe0d5fc06ed698d3cll, 0xaf85882d2576a038ll, 0xd55df8e515432941ll,
                0x5a3569bd451db2call, 0x20ed197575283bb3ll, 0xc49581ead523e8c2ll,
                0xbe4df122e51661bbll, 0x3125607ab548fa30ll, 0x4bfd10b2857d7349ll,
                0x4ad64994d625e4dll, 0x7e7514517d57d734ll, 0xf11d85092d094cbfll,
                0x8bc5f5c11d3cc5c6ll, 0x12b5926535897936ll, 0x686de2ad05bcf04fll,
                0xe70573f555e26bc4ll, 0x9ddd033d65d7e2bdll, 0xd28d7716adc8cfb9ll,
                0xa85507de9dfd46c0ll, 0x273d9686cda3dd4bll, 0x5de5e64efd965432ll,
                0xb99d7ed15d9d8743ll, 0xc3450e196da80e3all, 0x4c2d9f413df695b1ll,
                0x36f5ef890dc31cc8ll, 0x79a59ba2c5dc31ccll, 0x37deb6af5e9b8b5ll,
                0x8c157a32a5b7233ell, 0xf6cd0afa9582aa47ll, 0x4ad64994d625e4dall,
                0x300e395ce6106da3ll, 0xbf66a804b64ef628ll, 0xc5bed8cc867b7f51ll,
                0x8aeeace74e645255ll, 0xf036dc2f7e51db2cll, 0x7f5e4d772e0f40a7ll,
                0x5863dbf1e3ac9dell, 0xe1fea520be311aafll, 0x9b26d5e88e0493d6ll,
                0x144e44b0de5a085dll, 0x6e963478ee6f8124ll, 0x21c640532670ac20ll,
                0x5b1e309b16452559ll, 0xd476a1c3461bbed2ll, 0xaeaed10b762e37abll,
                0x37deb6af5e9b8b5bll, 0x4d06c6676eae0222ll, 0xc26e573f3ef099a9ll,
                0xb8b627f70ec510d0ll, 0xf7e653dcc6da3dd4ll, 0x8d3e2314f6efb4adll,
                0x256b24ca6b12f26ll, 0x788ec2849684a65fll, 0x9cf65a1b368f752ell,
                0xe62e2ad306bafc57ll, 0x6946bb8b56e467dcll, 0x139ecb4366d1eea5ll,
                0x5ccebf68aecec3a1ll, 0x2616cfa09efb4ad8ll, 0xa97e5ef8cea5d153ll,
                0xd3a62e30fe90582all, 0xb0c7b7e3c7593bd8ll, 0xca1fc72bf76cb2a1ll,
                0x45775673a732292all, 0x3faf26bb9707a053ll, 0x70ff52905f188d57ll,
                0xa2722586f2d042ell, 0x854fb3003f739fa5ll, 0xff97c3c80f4616dcll,
                0x1bef5b57af4dc5adll, 0x61372b9f9f784cd4ll, 0xee5fbac7cf26d75fll,
                0x9487ca0fff135e26ll, 0xdbd7be24370c7322ll, 0xa10fceec0739fa5bll,
                0x2e675fb4576761d0ll, 0x54bf2f7c6752e8a9ll, 0xcdcf48d84fe75459ll,
                0xb71738107fd2dd20ll, 0x387fa9482f8c46abll, 0x42a7d9801fb9cfd2ll,
                0xdf7adabd7a6e2d6ll, 0x772fdd63e7936bafll, 0xf8474c3bb7cdf024ll,
                0x829f3cf387f8795dll, 0x66e7a46c27f3aa2cll, 0x1c3fd4a417c62355ll,
                0x935745fc4798b8dell, 0xe98f353477ad31a7ll, 0xa6df411fbfb21ca3ll,
                0xdc0731d78f8795dall, 0x536fa08fdfd90e51ll, 0x29b7d047efec8728ll
        };
    
    
        acl_uint64 acl_hash_crc64(const void *buf, size_t len)
        {
        
            const unsigned char* ptr = (const unsigned char *) buf;
            acl_uint64 crc = INITIALCRC;
    
            while (len-- > 0) {
        
                crc = crc64_table[(int)((crc ^ *ptr++) & 0xff)] ^ (crc >> 8);
            }
    
            return crc;
        }
    }

# 测试 #

int main(void){
        
        const char * key = "aaaaa";
        size_t  len = strlen(key);
        acl_uint64 n = acl_hash_crc64(key, len);
        printf("%llu", n);
    
        return 0;
    }

![在这里插入图片描述][8c43a7c5c7d2426e93fc424ccbec7f2f.png]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70_pic_center]: /images/20220829/b587cdfdec4349a2a29f9749b2dfacd7.png
[golang]: https://blog.csdn.net/zhizhengguan/article/details/107949087
[8c43a7c5c7d2426e93fc424ccbec7f2f.png]: /images/20220829/cf6562c4a51a46b3807e9883a2ecdb48.png