Unless I had a bunch more formatting to do elsewhere, I would try to avoid sprintf(), which is quite costly code-wise.

Admittedly, the tostr()/rpt() pair are a bit inefficient and could be combined into something smaller -- a variation of:

/****************************************************************************
 *
 *    NAME: UsToStr
 * PURPOSE: Convert unsigned short to decimal string.
 *
 * SYNOPSIS:   void UsToStr(char *s, unsigned short bin, unsigned char n);
 *
 * DESCRIPTION:
 *
 *     The function stores a NUL-terminated string, in "n" + 1 (plus 1 for
 *     the NUL string terminator) successive elements of the array whose
 *     first element has the address "s", by converting "bin" to "n" decimal
 *     characters.
 *
 ****************************************************************************/

void UsToStr(char *s, unsigned short bin, unsigned char n)
{
    s += n;
    *s = '';

    while (n--)
    {
        *--s = (bin % 10) + '0';
        bin /= 10;
    }
}