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Suppose I have two variables which are both set to infinity
double l = std::numeric_limits<double>::infinity();
double r = std::numeric_limits<double>::infinity();
At another point in the code, I have a comparison of these two variables
if (l < r) {}
Is the result of this comparison properly defined in the library? (Within the logic of my program, I would expect the result to be false.)
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C allows us to define INFINITY as positive INFINITY or negative INFINITY .
Inf means infinity, and is the result of dividing a positive number by zero -- e.g., 1/0 → Inf. or computing a number larger than 1.796E308 (the largest number that your computer can represent in 64 bits) -- e.g. 1E307 * 100 → Inf.
In comparison operations, positive infinity is larger than all values except itself and NaN, and negative infinity is smaller than all values except itself and NaN. NaN is unordered: it is not equal to, greater than, or less than anything, including itself.
In floating-point calculations, NaN is not the same as infinity, although both are typically handled as special cases in floating-point representations of real numbers as well as in floating-point operations.
(Within the logic of my program, I would expect the result to be
false.)
According to this:
In comparison operations, positive infinity is larger than all values except itself and NaN
So you are indeed correct.
Note that this might not be valid if your compiler uses a different standard than IEEE 754, so make sure that std::numeric_limits<double>::is_iec559; returns true when in doubt.
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