cheking overflow

[quarkcode]

there is a function f
i need to check whether the value returned by f is positive or
negative
but if the number overflows and shows negative even when actually it
is positive
how can i check that the number is really negative?

[Flash Gordon]

quarkcode wrote, On 16/08/07 11:26:

there is a function f
i need to check whether the value returned by f is positive or
negative
but if the number overflows and shows negative even when actually it
is positive
how can i check that the number is really negative?

You will have to check for overflow in function f and return (or
otherwise make available) the status. Note that you generally need to
check whether an operation will overflow *before* doing the operation
rather than after, unsigned integer types being the exception.
--
Flash Gordon

[CBFalconer]

quarkcode wrote:

>
there is a function f. i need to check whether the value returned
by f is positive or negative but if the number overflows and shows
negative even when actually it is positive how can i check that
the number is really negative?

You can't. Once the overflow occurs all operation is classified as
"undefined behaviour". You have to detect the overflow before it
actually occurs. How to do this depends on the types and codes
involved.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>
--
Posted via a free Usenet account from http://www.teranews.com

[gw7rib]

On 16 Aug, 11:26, quarkcode <[e-mail]:

there is a function f
i need to check whether the value returned by f is positive or
negative
but if the number overflows and shows negative even when actually it
is positive
how can i check that the number is really negative?

One possibility might be for f to use a wider type internally, one
which is big enough that your routine won't overflow it. You can then
see whether the result is within the range of values you are able to
return from f - if it is not, then f could flag up an error somehow,
or you could replace the actual value with an artificial one (eg
INT_MAX).

I'll leave the details to you...

Paul.

[SM Ryan]

quarkcode <sh********@gmail.comwrote:
# there is a function f
# i need to check whether the value returned by f is positive or
# negative
# but if the number overflows and shows negative even when actually it
# is positive
# how can i check that the number is really negative?

ANSI C doesn't require overflow detection. You would have used to
system dependent facilities, if they exist, though I've never heard
of a C compiler that can report integer overflow.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
Wow. A sailboat.

[quarkcode]

On Aug 16, 6:32 am, CBFalconer <[e-mail]:

quarkcode wrote:

there is a function f. i need to check whether the value returned
by f is positive or negative but if the number overflows and shows
negative even when actually it is positive how can i check that
the number is really negative?

You can't. Once the overflow occurs all operation is classified as
"undefined behaviour". You have to detect the overflow before it
actually occurs. How to do this depends on the types and codes
involved.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account fromhttp://www.teranews.com

suppose i calculate f(x),the function being long enough and i
calculate using link list.Can i know at what point dring the
calculation is it going to overflow
if i want to trap overflow before it actually happens

[pete]

quarkcode wrote:

>
On Aug 16, 6:32 am, CBFalconer <[e-mail]:

quarkcode wrote:

there is a function f. i need to check whether the value returned
by f is positive or negative but if the number overflows and shows
negative even when actually it is positive how can i check that
the number is really negative?

You can't. Once the overflow occurs all operation is classified as
"undefined behaviour". You have to detect the overflow before it
actually occurs. How to do this depends on the types and codes
involved.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account fromhttp://www.teranews.com

suppose i calculate f(x),the function being long enough and i
calculate using link list.Can i know at what point dring the
calculation is it going to overflow
if i want to trap overflow before it actually happens

What is your procedure for "calculate using link list"?

What kind of operators and operands are invloved in
"calculate using link list"?

What's involved in "calculate using link list"
is pretty nebulous from my point of view.

--
pete

[CBFalconer]

quarkcode wrote:

CBFalconer <[e-mail]:

>quarkcode wrote:

>>there is a function f. i need to check whether the value returned
by f is positive or negative but if the number overflows and shows
negative even when actually it is positive how can i check that
the number is really negative?

You can't. Once the overflow occurs all operation is classified as
"undefined behaviour". You have to detect the overflow before it
actually occurs. How to do this depends on the types and codes
involved.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account fromhttp://www.teranews.com

suppose i calculate f(x),the function being long enough and i
calculate using link list.Can i know at what point dring the
calculation is it going to overflow
if i want to trap overflow before it actually happens

Why is my sig, and my ISPs added sig, still present here? They are
plainly marked with sig markers. Are you crippled in some manner
that prevents operation of the selection and deletion keys? Is
this the same reason you fail to add blanks between sentences, and
fail to capitalize the personal pronoun 'I'?

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account from http://www.teranews.com