Re: moot and unposixy error message

[Andreas Schwab]

Benno Schulenberg <address@hidden> writes:

> Hi,
>
> In src/od.c around line 1820 it says this:
>
>   if (limit_bytes_to_format)
>     {
>       end_offset = n_bytes_to_skip + max_bytes_to_format;
>       if (end_offset < n_bytes_to_skip)
>         error (EXIT_FAILURE, 0, _("skip-bytes + read-bytes is too large"));
>     }
>
> Since max_bytes_to_format cannot be negative, the second 'if' will 
> never trigger, so the whole six lines are moot.

But the sum can overflow, and since the involved types are unsigned this
has defined (wrap-around) behaviour.

> Further, the Open Group says that 'od' should not produce an error 
> when '-j' plus '-N' is longer than the file, so the above section 
> can be removed.

This is a good point, however.  But end_offset should then be set to
(uintmax_t)-1 on overflow.

Andreas.

-- 
Andreas Schwab, SuSE Labs, address@hidden
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."