What is -1. # IND and -1. # J?

Any experienced programmer knows that the standard for representing floating-point values ​​( IEEE 754 ) leaves several reserved values ​​corresponding to non-numbers (NaN, not-a-number). The Visual C standard library prints non-numbers like this:

Printed	Means
1.#INF	Positive infinity
-1.#INF	Negative infinity
1.#SNAN	Positive signal non-number (signaling NaN)
-1.#SNAN	Negative signal non-number (signaling NaN)
1.#QNAN	Positive non-signal non-number (quiet NaN)
-1.#QNAN	Negative non-signal non-number (quiet NaN)
1.#IND	Positive uncertainty
-1.#IND	Negative uncertainty

Positive and negative infinity can be obtained when overflow occurs as a result of arithmetic - for example, when dividing by zero, or when taking the logarithm from a positive zero. (According to the IEEE standard, any floating point value has a definite sign - not only non-numbers exist in positive and negative variants, but also two zeros.)

Signal and non-signal non-numbers, as a rule, are not obtained as a result of calculations, but are generated by the program intentionally - for example, in C ++ you can get them by calling the signaling_NaN() or quiet_NaN() methods of the std::numeric_limits. , -- " ", " " .. - -, .. , .

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