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Checking Overflow/Underflow on math

How does one check on overflow/underflow for the following C++ types: long, short, float, double, for add, subtract, multiply, divide. Example:      long L;      L = 2147483647;
      L++;      // Check flag to see if it overflowed.Using assembly language, I can easily accomplish this under Intel/Win32 via:      seto al      mov fOverflow, alAnd for floating point, I can use _clearfp( ). However, this is Microsoft compiler and Intel CPU specific. How does one do this in plain C++??Is there a way?More sample code:      long L;
      L = 2147483647;
      L++
----
      short I;
      I = 32767;
      I++;
----
      double d;
      d = 1.7976931348623158e+308;
      d = d * d;
----
      float f;
      f = 16777216.000000;
      f++;

chensu

There is a Microsoft extension (Structured Exception Handling) in Visaul C++ to do it.

__try
{
...
}
__except( GetExceptionCode() == STATUS_INTEGER_OVERFLOW )
{
}

You can get more information by seeing the documentation that comes with Visual C++:
Visaul C++ Books/C/C++/Programming Techniques/Structured Exception Handling/.

Shrif

ASKER

I was very clear in stating in my question that I am seeking a non-platform specific answer. I cannot rely on assembly language, or Visual C++.In addition, so that it is clear, I need the solution to also work for the largest possible type as well. I say this because an obvious way to check for overflow on an integer is to perform the same operation with a larget size, a long, and compare the results. This technique will fail for the largest size, double, which also needs to be handled.

md041797

There is an extension to ANSI C that provides for signal (SIGFPE), but it's not guarantted to be implemented by every compiler, and the handling of errno is not standardized either. Anyway, it would cause a jump to your handler and that's not good for C++.

I would recommend an explicit check as follows:

Check = L = 2147483647;
L++;
if (Check != --L) //then overflow

Shrif

ASKER

The proposed solution does not work. If you add 1 to the value, you may overflow -- that's true, but that doesn't mean that subtracting from the result will not return you back to where you started. It will. Sorry.

ASKER CERTIFIED SOLUTION

icd

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