Adding two large numbers

[Waldermort]

This is the same with any data type, when 1 large number is added to another and the result is larger than the data type can hold, it wraps around. i.e. ULONG size1 = 0xFFFFFF00; ULONG size2 = 0xFFFFFF00; size1 += size2; // == 0xFFFFFE00 The output is less than the input. I want to check for this problem and if it's there I would prefer the output to be the max value the data type can hold. What is the best way to approach this?

[Ahmed Ismail Mohamed]

waldermort wrote:

ULONG size1 = 0xFFFFFF00; ULONG size2 = 0xFFFFFF00;

if you divede both size1 and size by a big number that make you sure that you can add and you still in the range of long. size1 = size1/n; size2 = size2/n;

waldermort wrote:

size1 += size2; // == 0xFFFFFE00

adding in this line will not make a problem then finally, when you want to output the final value , make the value the program do it time the number you devide by it: ex: textbox1.text = Tostring(size2 * n) // n is the number you devided by it. I hope it work properly with you. regards;:) ** Ahmed Ismail **

[Waldermort]

That doesn't work, it produces exactly the same result as simply adding them: ULONG max1 = 0xFFFFFF00; ULONG max2 = 0xFFFFFF00; max1 = max1/4; max2 = max2/4; max2 += max1; max2 *= 4; // == 0xFFFFFE00 The only way I have found is to cast them to a larger data type and check the value using an if else block if ( ((UINT64)max1 + (UINT64)max2) > 0xFFFFFFFF ) max2 = 0xFFFFFFFF; else max2 += max1; But I'm sure there must be a more accurate way of doing it.

[Nader Elshehabi]

Hello Well, if you have some assembly background you'd remember that there is a bit in the status register called overflow bit to check for this error. Anyway, I know how to check for overflow in Assembly and C#, but sorry, my C++ is too rusty to remember how to do it in C++:-D. You are right, there is a better way to detect overflow, yet I will provide you with a simpler way of detecting it. Usualy the overflow result is smaller than any of the two operands. So, try this:

ULONG size1 = 0xFFFFFF00;
ULONG size2 = 0xFFFFFF00;
size1 += size2; // == 0xFFFFFE00

if( size1 < size2)
size1 = 0xFFFFFFFF;

Remember, maximum value of each type is totally OS dependant. Keep that in mind.:) If someone got a better approach, please post. I'll try to remember how to check overflow in C++. If I got anything, I'll keep you posted.

Regards:rose:

[toxcct]

use the header <LIMITS.h> with this, you can know the types max and min values, and some other informations for floating points types.

---

TOXCCT >>> GEII power

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[Waldermort]

That probably is a better way of doing it. Thinking about it, the output would always be smaller. If you remember the better way, please post it. I would love to know.

[Rick York]

You could do something like this : _int64 sum = (_int64)size1 + (_int64)size2; if( sum > ULONG_MAX ) TRACE( "an overflow occurred\n" ); else size1 = (ULONG)sum;

[Stephen Hewitt]

Try this: ULONG size1 = 0xFFFFFF00; ULONG size2 = 0xFFFFFF00; ULONG sizeR = size1 + size2; // == 0xFFFFFE00 if (sizeR < max(size1, size2)) {     // Overflow. }

Steve

[MayankT]

try this: if (MAXVAL - size1 < size2) { //overflow } else { size1 += size2; } MAXVAL can be obtained from limits.h as toxcct said.

---------------------- Mayank Thakore Learning C++ - since 1998 They didn't print my card right; so I resigned.