bkdrhash demo

bkdrhash demo

/* Start of bkdrhash.c */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <unistd.h>
#include <getopt.h>

#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif /* End of defined(__cplusplus) || defined(c_plusplus) */

unsigned long BKDRHash(unsigned long seed, const char *str, unsigned int len)
{
    if (str == NULL || seed == 0 || len == 0) {
        return 0;
    }
    
    static const int c1 = 0xcc9e2d51;
    static const int c2 = 0x1b873593;
    static const int r1 = 15;
    static const int r2 = 13;
    static const int m = 5;
    static const int n = 0xe6546b64;
    unsigned long hash = seed;

    const int nblocks = len / 4;
    const int *blocks = (const int *)str;
    int i;
    for (i = 0; i < nblocks; i++)
    {
        int k = blocks[i];
        k *= c1;
        k = (k << r1) | (k >> (32 - r1));
        k *= c2;

        hash ^= k;
        hash = ((hash << r2) | (hash >> (32 - r2))) * m + n;
    }

    const int *tail = (const int *)(str + nblocks * 4);
    int k1 = 0;

    switch (len & 3)
    {
        case 3:
            k1 ^= tail[2] << 16;
        case 2:
            k1 ^= tail[1] << 8;
        case 1:
            k1 ^= tail[0];

            k1 *= c1;
            k1 = (k1 << r1) | (k1 >> (32 - r1));
            k1 *= c2;
            hash ^= k1;
    }

    hash ^= len;
    hash ^= (hash >> 16);
    hash *= 0x85ebca6b;
    hash ^= (hash >> 13);
    hash *= 0xc2b2ae35;
    hash ^= (hash >> 16);

    return hash;
}


#if defined(__cplusplus) || defined(c_plusplus)
}
#endif /* End of defined(__cplusplus) || defined(c_plusplus) */

int main(int argc, char *argv[])
{
    if ( argc != 3 ) {
        fprintf(stderr, "Using: %s 3 user111
", argv[0]);
        return -1;
    }
    
    long seed = atol(argv[1]);
    const char *str = argv[2];
    if (seed <= 0) {
        fprintf(stderr, "Error: %s
", "seed must be greater than zero");
        return -1;
    }
    if (str == NULL) {
        fprintf(stderr, "Error: %s
", "string cannot be empty");
        return -1;
    }
    fprintf(stdout, "Info: seed(%ld), str(%s)
", seed, str);
    
    unsigned long result = BKDRHash((unsigned long)seed, str, strlen(str));
    if ( result == 0 ) {
        fprintf(stderr, "Error: %s
", "BKDRHash calculation failed");
        return -1;
    }
    fprintf(stdout, "Info: BKDRHash result(%lu)
", result);
    
    return 0;
}

/* End  of bkdrhash.c */

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