On 01/27/2011 11:42 PM, Paul Eggert wrote:
> If it could be done just as clearly by other means, that would
> be OK too.
To try to do that, I installed the following:
---
ChangeLog| 13 +
lib/intprops.h |4 ++--
lib/mktime.c |2 +-
lib/strtol.c
On Fri, Jan 28, 2011 at 06:57:22PM +0100, Bruno Haible wrote:
> Rich Felker wrote:
> > Testing which of the three allowable signed integer
> > representations is used is easy: compare ~(t)1 against and -(t)1 and
> > -(t)2.
>
> Testing which of the three signed integer representations is in use
> i
Rich Felker wrote:
> Testing which of the three allowable signed integer
> representations is used is easy: compare ~(t)1 against and -(t)1 and
> -(t)2.
Testing which of the three signed integer representations is in use
is not even needed: Your formula
t) 1 << (sizeof (t) * CHAR_BIT - 2)) -
On Thu, Jan 27, 2011 at 11:42:25PM -0800, Paul Eggert wrote:
> On 01/27/2011 02:08 PM, Rich Felker wrote:
> > I mean to say that left-shifting a negative value *at all* is
> > undefined behavior. I doubt gcc will ever break it, but why not use my
> > version of the code that's 100% safe and never i
On 01/27/2011 02:08 PM, Rich Felker wrote:
> I mean to say that left-shifting a negative value *at all* is
> undefined behavior. I doubt gcc will ever break it, but why not use my
> version of the code that's 100% safe and never invokes undefined
> behavior?
Your version of the code provokes simil
On Thu, Jan 27, 2011 at 07:42:10PM +0100, Bruno Haible wrote:
> Do you mean to say that GCC produces undefined behaviour for shifts of
> negative values, even those where the result is negative (no overflow)?
> I've never seen a sign of that.
I mean to say that left-shifting a negative value *at a
Rich Felker wrote:
> > # define TYPE_MAXIMUM(t) \
> > ((t) (! TYPE_SIGNED (t) \
> > ? (t) -1 \
> > : ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1
>
> The last line of this macro has UB due to signed integer overflow in
> the << operation.
No there is no overflow here. The ~ oper
On 01/27/11 10:15, Eric Blake wrote:
> In other words, the problem is not about overflow, but about undefined
> behavior.
You're right that the behavior is not defined, but this should
not be a problem in practice, any more than the * CHAR_BIT business
should be a problem in practice (that also re
On 01/27/2011 10:57 AM, Paul Eggert wrote:
# define TYPE_MAXIMUM(t) \
((t) (! TYPE_SIGNED (t) \
? (t) -1 \
: ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1
>> The last line of this macro has UB due to signed integer overflow in
>> the << operation.
>
> No it doe
On 01/27/11 09:28, Rich Felker wrote:
> On Thu, Jan 27, 2011 at 08:14:56AM -0700, Eric Blake wrote:
>> > # define TYPE_MINIMUM(t) \
>> > ((t) (! TYPE_SIGNED (t) \
>> > ? (t) 0 \
>> > : TYPE_SIGNED_MAGNITUDE (t) \
>> > ? ~ (t) 0 \
>> > : ~ (t) 0 << (sizeof (t) * CHA
On Thu, Jan 27, 2011 at 08:14:56AM -0700, Eric Blake wrote:
> # define TYPE_MINIMUM(t) \
> ((t) (! TYPE_SIGNED (t) \
> ? (t) 0 \
> : TYPE_SIGNED_MAGNITUDE (t) \
> ? ~ (t) 0 \
> : ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
> # define TYPE_MAXIMUM(t) \
> ((t) (! TYPE
[adding bug-gnulib, as requested]
On 01/26/2011 10:21 PM, Rich Felker wrote:
> The configure test for mktime (m4/mktime.m4) contains the following
> code:
>
> for (;;)
> {
> t = (time_t_max << 1) + 1;
> if (t <= time_t_max)
> break;
> time_t_max = t;
> }
>
> T
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