Re: PATCH [4/n]: Support 64bit time_t and 32bit long

[Paul Eggert <eggert at cs dot ucla dot edu>]

On 03/15/2012 01:17 PM, H.J. Lu wrote:
>    days = *t / SECS_PER_DAY;
> +  if (days != *t / SECS_PER_DAY)
> +    goto overflow;

This is not a reliable way to test for integer overflow.
Since 'days' is signed, the compiler can assume that the
assignment does not overflow, and can ignore the 'if' entirely.

Instead, I suggest changing 'days' to be of type time_t,
so that overflow cannot occur here.

> @@ -65,6 +67,9 @@ __offtime (t, offset, tp)
>        /* Guess a corrected year, assuming 365 days per year.  */
>        long int yg = y + days / 365 - (days % 365 < 0);
>  
> +      if (yg < 0)
> +	goto overflow;
> +

Similarly here.