Embedded Software Engineer Solves FizzBuzz

fizzbuzz.c

#include <stdio.h>
 
enum
{
    FIZZ = 1,
    BUZZ = 2
};
 
static int get_natural(const char *val, unsigned int *out)
{
    unsigned int prev = *out = 0;
 
    if (*val == '\0')
    {
        return 0;
    }
 
    while (isdigit(*val))
    {
        unsigned int dig = *val - '0';
        *out *= 10;
        *out += dig;
 
        if ((*out - dig) / 10 != prev)
        {
            return 0;
        }
 
        prev = *out;
        ++val;
    }
 
    return *val == '\0';
}
 
int main(int argc, const char *argv[])
{
    unsigned int max;
 
    if ((argc != 2) || (!get_natural(argv[1], &max)))
    {
        puts("Usage:\r\n  fizzbuzz <max-natural-number>");
    }
    else if (max > 0)
    {
        register unsigned int cur = max;
        static const char *str[] = { "", "Fizz", "Buzz" };
 
        for (;;)
        {
            unsigned int rnd = 0x2486, msk = 0x3659;
 
            while (rnd)
            {
                register unsigned int x = rnd & 3;
 
                if (x > cur)
                {
                    x = cur;
                }
 
                while (x--)
                {
                    printf("%d ", max - cur + 1);
                    --cur;
                }
 
                if (!cur)
                    goto end;
 
                printf("%s%s ", str[msk & FIZZ], str[msk & BUZZ]);
                --cur;
                rnd >>= 2;
                msk >>= 2;
            }
        }
 
end:
        printf("\r\n");
    }
 
    return 0;
}