Jenkins hash

jhash.c

/* 
 * jhash.c - Simple Jenkins hash.
 * 
 * Copyright (C) 2006. Bob Jenkins (bob_jenkins@burtleburtle.net)
 * http://burtleburtle.net/bob/hash/
 *
 * Sources taken from Linux kernel implementation.
 * Copyright (C) 2009-2010 Jozsef Kadlecsik (kadlec@blackhole.kfki.hu)
 *
 * Turned into userspace program by avd
 * Copyright (C) 2014 Alex Dzyoba <avd@reduct.ru>
 *  
 * This code as original Bob's code is in public domain.
 */
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

/* An arbitrary initial parameter */
#define JHASH_INITVAL           0xdeadbeef

typedef unsigned int u32;

#define rol32(a,s) a << s

/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
#define __jhash_final(a, b, c)                  \
{                                               \
        c ^= b; c -= rol32(b, 14);              \
        a ^= c; a -= rol32(c, 11);              \
        b ^= a; b -= rol32(a, 25);              \
        c ^= b; c -= rol32(b, 16);              \
        a ^= c; a -= rol32(c, 4);               \
        b ^= a; b -= rol32(a, 14);              \
        c ^= b; c -= rol32(b, 24);              \
}

/* jhash_3words - hash exactly 3, 2 or 1 word(s) */
static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
{
        a += JHASH_INITVAL;
        b += JHASH_INITVAL;
        c += initval;

        __jhash_final(a, b, c);

        return c;
}

static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
{
        return jhash_3words(a, b, 0, initval);
}

static inline u32 jhash_1word(u32 a, u32 initval)
{
        return jhash_3words(a, 0, 0, initval);
}

void usage()
{
    fprintf(stderr, "Usage: ./jhash <integer to hash>\n");
    fprintf(stderr, "Input integer must fit in 4 bytes (u32).\n");
}


int main(int argc, const char *argv[])
{
    u32 hash;
    u32 val;
    char *errptr = NULL;

    if(argc != 2)
    {
        usage();
        return EXIT_FAILURE;
    }

    val = strtol(argv[1], &errptr, 10);
    if( *errptr != 0 || errno == ERANGE )
    {
        usage();
        return EXIT_FAILURE;
    }
    
    hash = jhash_1word(val, 0x16278182);
    printf("%08x\n", hash);
    return EXIT_SUCCESS;
}