Plan 9 from Bell Labs’s /usr/web/sources/contrib/anothy/src/lib/djb-ape/byte/fmt_uint0.c
#include "fmt.h" unsigned int fmt_uint0(char* s,unsigned int u,unsigned int n) { unsigned int len; len = fmt_uint(FMT_LEN,u); while (len < n) { if (s) *s++ = '0'; ++len; } if (s) fmt_uint(s,u); return len; }