A Fizz Buzz program

prog3.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static char num_fig_buf[4096]; // the size must be > 3 * 1000

unsigned int keta(unsigned int i)
{
    unsigned int k = 0;
    while (1) {
        i /= 10;
        ++k;
        if (i == 0) {
            return k;
        }
    }
}

void sprint15(char *buf, unsigned int i, char *num_places[8])
{
    unsigned int offset = keta(i) - 3;
    char *p = buf;

    num_places[0] = p + offset; p += sprintf(buf, "%d\n", i);
    num_places[1] = p + offset; p += sprintf(p, "%d\n" "Fizz\n", i + 1);
    num_places[2] = p + offset; p += sprintf(p, "%d\n" "Buzz\n" "Fizz\n", i + 3);
    num_places[3] = p + offset; p += sprintf(p, "%d\n", i + 6);
    num_places[4] = p + offset; p += sprintf(p, "%d\n" "Fizz\n" "Buzz\n", i + 7);
    num_places[5] = p + offset; p += sprintf(p, "%d\n" "Fizz\n", i + 10);
    num_places[6] = p + offset; p += sprintf(p, "%d\n", i + 12);
    num_places[7] = p + offset; p += sprintf(p, "%d\n" "FizzBuzz\n", i + 13);
}

void sfill15(char *num_places[8], unsigned int i)
{
    i = i % 1000;

    memcpy(num_places[0], &num_fig_buf[i * 3], 3);
    memcpy(num_places[1], &num_fig_buf[(i + 1) * 3], 3);
    memcpy(num_places[2], &num_fig_buf[(i + 3) * 3], 3);
    memcpy(num_places[3], &num_fig_buf[(i + 6) * 3], 3);
    memcpy(num_places[4], &num_fig_buf[(i + 7) * 3], 3);
    memcpy(num_places[5], &num_fig_buf[(i + 10) * 3], 3);
    memcpy(num_places[6], &num_fig_buf[(i + 12) * 3], 3);
    memcpy(num_places[7], &num_fig_buf[(i + 13) * 3], 3);
}

int main()
{
    static char stdio_buffer[64 * 1024];
    setvbuf(stdout, stdio_buffer, _IOFBF, sizeof(stdio_buffer));

    char buf[4 * 1024]; // the size must be > (10 * 8 + 4 * 8 + 15) * 100
    char *num_places[8];

    unsigned int i;

    for (i = 0; i < 1000; ++i) {
        sprintf(&num_fig_buf[0] + i * 3, "%03d", i);
    }

    i = 1;
    while (i < 1000) {
        sprint15(buf, i, num_places);
        fputs(buf, stdout);
        i += 15;
    }
    sprint15(buf, i, num_places);

    while (1) {
        unsigned int i_start_mil = i / 1000;
        unsigned int i_end_mil = (i + 15) / 1000;
        if (i_start_mil == i_end_mil) {
            sfill15(num_places, i);
            fputs(buf, stdout);
            i += 15;
        } else {
            sprint15(buf, i, num_places);
            fputs(buf, stdout);
            i += 15;
            sprint15(buf, i, num_places);
        }
    }

    return 0;
}