Thread: How to check 32 bit limit

Hi all,
can u help me how to find if the sum of two numbers X and Y would cross the 32 bit limit. My development system has all registers of 32 bits and checking them as:

if (X+Y) > 0xFFFFFFFF

doesn't help because the system then has to add the numbers for checking and if it did so, in case the sum is over 32 bits, the counter will roll over zero.

Code:

if( 0xFFFFFFFF - X >= Y )
    it will fit!
else
    it won't!

Subtract one from the maximum. Compare that value to the other.

[edit]
*forgot to allow for a perfect fit. (ie MAX is 10, X and Y are 5)
[/edit]

[edit2]
Or if we prefer just the simple check, instead of the ugly >=

Code:

if( Y > 0xFFFFFFFF - X )
    it won't fit!
else
    it will fit!

[/edit2]


Quzah.

I suppose you could do this:

Code:

z = x + y;

if ( z - x != y )
it crossed the limit;

I have no idea if that would work, but it's worth a try.


[EDIT]

Hahaha, quzah's is heaps better than mine - use that one. :P

yeah... i think it will work...
Thanks buddy.