Function posrelat

deps/lua/src/lstrlib.c:36–40

static ptrdiff_t posrelat (ptrdiff_t pos, size_t len) {
  /* relative string position: negative means back from end */
  if (pos < 0) pos += (ptrdiff_t)len + 1;
  return (pos >= 0) ? pos : 0;
}


static int str_sub (lua_State *L) {