Hand-rolled FizzBuzz

fizz.c

#include <string.h>
#include <unistd.h>

#define ALIGNED_BUF 65536
#define DELIM ' '
#define MAX_DIGITS 20 /* 64-bit */

typedef unsigned int fizz_t;

__attribute__((always_inline))
static inline const char* sernum(fizz_t c)
{
    static char serbuf[MAX_DIGITS + 1] = { 0 };
    char *f = serbuf + sizeof(serbuf) - 2;

    for (; c; *f = c % 10 + '0', c /= 10)
    {
        --f;
    }

    return f;
}

int main(void)
{
    fizz_t cur = 1;
    __attribute__((aligned(4096))) static char buf[ALIGNED_BUF + ((MAX_DIGITS + 1) * 15)] = { 0 };
    char *off = buf;

    for (;;)
    {
        while (off - buf < ALIGNED_BUF)
        {
            if (__builtin_expect(cur == 0, 0))
            {
                goto end;
            }

            for (const char *c = sernum(cur++); *c; *off++ = *c++)
                ;

            *off++ = DELIM;
            for (const char *c = sernum(cur++); *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            ++cur;
            for (const char *c = "Fizz"; *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            for (const char *c = sernum(cur++); *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            ++cur;
            for (const char *c = "Buzz"; *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            ++cur;
            for (const char *c = "Fizz"; *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            for (const char *c = sernum(cur++); *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            for (const char *c = sernum(cur++); *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            ++cur;
            for (const char *c = "Fizz"; *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            ++cur;
            for (const char *c = "Buzz"; *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            for (const char *c = sernum(cur++); *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            ++cur;
            for (const char *c = "Fizz"; *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            for (const char *c = sernum(cur++); *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            for (const char *c = sernum(cur++); *c; *off++ = *c++)
                ;
            *off++ = DELIM;

            ++cur;
            for (const char *c = "FizzBuzz"; *c; *off++ = *c++)
                ;
            *off++ = DELIM;
        }

        write(1, buf, ALIGNED_BUF);
        memcpy(buf, buf + ALIGNED_BUF, (off - buf) % ALIGNED_BUF);
        off -= ALIGNED_BUF;
    }

end:
    *off++ = '\n';
    write(1, buf, off - buf);

    return 0;
}