What Do 1.#INF00, -1.#IND00, -1.#IND, and 1.$NaN Mean in IEEE Floating-Point C ?

IEEE Floating-Point Exceptions in C

Understanding 1.#INF00, -1.#IND00, -1.#IND, and 1.$NaN

When working with floats in C code, encountering values like 1.#INF00, -1.#IND00, -1.#IND, or 1.$NaN can be puzzling. These values represent specific conditions encountered during floating-point operations.

1.#INF00 and -1.#INF00

These values represent infinity. 1.#INF00 indicates positive infinity, while -1.#INF00 represents negative infinity. They occur when the result of an operation would exceed the finite limits of double-precision floating-point arithmetic. For instance, dividing 1 by 0 yields 1.#INF00.

-1.#IND and -1.#IND00

These values represent "indeterminate". They occur when an operation results in a mathematically undefined value, such as the square root of a negative number. Both Windows and Linux display -1.#IND for these cases.

1.$NaN

This value represents "Not a Number". It is the generic term for values that are not valid numbers, such as the result of dividing 0 by 0, multiplying 0 by infinity, or dividing infinity by infinity. Windows displays -1.#IND for NaNs, while Linux displays nan.

Causes of Invalid Values

Invalid values can arise from:

• Overflow: When an operation would produce a result that exceeds the representable range of floating-point numbers.
• Underflow: When an operation would produce a result that is too close to 0 to be represented accurately.
• Illegal Operations: Operations that do not have a valid mathematical result, such as taking the square root of a negative number.

Debugging and Usage

Invalid values can help with debugging by indicating unexpected or illegal operations. By understanding what these values represent, programmers can identify and fix errors. For example, encountering 1.#INF00 may suggest a potential overflow issue that needs to be addressed.

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