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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）

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;
}