simple hash:

x.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <fcntl.h>
#include <sys/stat.h>

#define PATH "numbers.txt"
#define CHUNK_SIZE 4096

static inline unsigned int simple_hash(char ** s)
{
        register unsigned int h = 52543;
        char * p = *s;
        int c;

        do {
                c = *p++;
                h = ((c & 0xf) ^ ((*p >> 4) & 0xf)) + (h << 1);
                h += ((c & 0xf0) + *p) * 11;
                h ^= (c * *p) << 19;
        } while(*p != '\n');
        *s = p;

        return h;
}

int main(int argc, char * argv[])
{
        struct stat stats;

        stat(PATH, &stats);
        char *buf = malloc(stats.st_size + 1);
        char *cur = buf;
        char *end = buf + stats.st_size;

        clock_t start, stop;
        int c = 0;

        start = clock();

        // Load file into memory
        int fp = open(PATH, O_RDONLY);

        if(fp == -1)
                goto _return;

        off_t in;
        while ((in = read(fp, cur, CHUNK_SIZE))) {
                cur += in;
        }
        cur[0] = '\n';
        // Do the hashing
        cur = buf;
        if(argc-1) {
                while(cur < end) {
                        simple_hash(&cur);
                        ++c;
                }
        }
        else {
                while(cur < buf + stats.st_size) {
                        printf("%u\n", simple_hash(&cur));
                        ++c;
                }
        }

        close(fp);
        stop = clock();
        printf("%d in %ld ms\n", c,
                   (long)(stop - start) * 1000 / CLOCKS_PER_SEC);

_return:
        return 0;
}