[showdead]

Well, there is this approach:

    #include <stdio.h>
    #include <stdint.h>
    
    #define FIZZ(x)         (x & 0x0924)
    #define BUZZ(x)         (x & 0x0210)
    #define FIZZBUZZ(x)     (x & 0x4000)
    #define NONE(x)         (x & 0x34cb)
    
    void fizzbuzz(size_t n_max)
    {
        uint32_t x = 1;
        for (size_t i = 1; i <= n_max; i++)
        {
            if (FIZZ(x))
              printf("fizz\n");
            if (BUZZ(x))
              printf("buzz\n");
            if (FIZZBUZZ(x))
              printf("fizzbuzz\n");
            if (NONE(x))
              printf("%d\n", i);
            x <<= 1;
            x |= (x >> 15);
        }
    }
    
    int main(int argc, char **argv)
    {
        fizzbuzz(100);
    }

It's less costly than integer division, and I'm not sure it's what you had in mind. The output here still duplicates the strings.

[raphlinus]

Tada! That's very close to what I had in mind. The only difference: you can fizz on 4924, buzz on 4210, none on 34cb, then always \n. Also, you have 3 ops to calculate the rotation, and that can be replaced by (0x8001 * x) >> 1 (for uint16_t x), but with tweaking of the masks because it's rotating right.

Congrats!