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After performing a mathematical operation, for say, multiplying two integers, is it possible to access the overflow flag register in a CPU with C++ ? If not what are other fast ways to check for an overflow ?
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Detecting Overflow and Underflow in CIf both numbers are positive and the sum is negative, that means there is an overflow, so we return -1 else; if both numbers are negative and the sum is positive, that also means there is an overflow, so we return -1 else, no overflow.
An integer overflow occurs when you attempt to store inside an integer variable a value that is larger than the maximum value the variable can hold. The C standard defines this situation as undefined behavior (meaning that anything might happen).
In computer processors, the overflow flag (sometimes called the V flag) is usually a single bit in a system status register used to indicate when an arithmetic overflow has occurred in an operation, indicating that the signed two's-complement result would not fit in the number of bits used for the result.
No, generally it's impossible. Some CPUs don't even have such a flag (e.g. MIPS).
The link provided in one of the comments will give you ideas on how you can do overflow checks.
Remember that in C and C++ signed integer overflows cause undefined behavior and legally you cannot perform overflow checks after the fact. You either need to use unsigned arithmetic or do the checks before arithmetic operations.
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You'd have to do the operation and check the overflow bit in inline assembly. You could do that and jump to a label on overflow, or (more generally but less efficiently) set a variable if it overflowed.
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