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What is the most reliable way to detect whether the architecture uses one's or two's complement representation in C++?
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C and C++ as specified, however, are not two's complement. Signed integers currently allow the existence of an extraordinary value which traps, extra padding bits, integral negative zero, and introduce undefined behavior and implementation-defined behavior for the sake of this extremely abstract machine.
A two's-complement number system encodes positive and negative numbers in a binary number representation. The weight of each bit is a power of two, except for the most significant bit, whose weight is the negative of the corresponding power of two.
You shouldn't have to worry - there aren't too many ones complement machines out there :)
But the easiest thing might be to compare "-1" with ~0.
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