Style tweaks and add a warning about NUL-termination

 * buf, up to max_len digits, and returns the actual number of digits written.

 * If there is insufficient space, it will write nothing and return 0.

 *

 * This function DOES NOT add a terminating NUL character to its output: be

 * careful!

 *

 * This accepts an unsigned int because format_helper_exit_status() needs to

 * call it with a signed int and an unsigned char, and since the C standard

 * does not guarantee that an int is wider than a char (an int must be at

 * can't assume a signed int is sufficient to accomodate an unsigned char.

 * Thus, format_helper_exit_status() will still need to emit any require '-'

 * on its own.

 *

 * For most purposes, you'd want to use tor_snprintf("%x") instead of this

 * function; it's designed to be used in code paths where you can't call

 * arbitrary C functions.

 */

int

format_hex_number_for_helper_exit_status(unsigned int x, char *buf,

                                         int max_len)

      tmp >>= 4;

      ++len;

    }

  } else {

    len = 1;

  }

  else len = 1;

  /* Bail if we would go past the end of the buffer */

  if (len > max_len)

 * CHILD_STATE_* macros for definition), and SAVED_ERRNO is the value of

 * errno when the failure occurred.

 */

void

format_helper_exit_status(unsigned char child_state, int saved_errno,

                          char *hex_errno)