Editing NaN (section)

=== Operations generating NaN ===
There are three kinds of operations that can return NaN:<ref>{{cite web|url=http://citeseer.ist.psu.edu/viewdoc/summary?doi=10.1.1.39.2736|author=David Goldberg|title= What Every Computer Scientist Should Know About Floating-Point|year=1991}}</ref>

* Most operations with at least one NaN operand.
* [[Indeterminate form]]s:
** The divisions {{math|(±0) / (±0)}} and {{math|(±∞) / (±∞)}}.
** The multiplications {{math|(±0) × (±∞)}} and {{math|(±∞) × (±0)}}.
** Remainder {{math|''x'' % ''y''}} when {{math|''x''}} is an infinity or {{math|''y''}} is zero.
** The additions {{math|(+∞) + (&minus;∞)}}, {{math|(&minus;∞) + (+∞)}} and equivalent subtractions {{math|(+∞) &minus; (+∞)}} and {{math|(&minus;∞) &minus; (&minus;∞)}}.
** The standard has alternative functions for powers:
*** The standard {{code|pow}} function and the integer exponent {{code|pown}} function define {{math|[[zero to the power of zero|0<sup>0</sup>]]}}, {{math|1<sup>∞</sup>}}, and {{math|∞<sup>0</sup>}} as {{math|1}}.
*** The {{code|powr}} function defines all three indeterminate forms as invalid operations and so returns NaN.
* Real operations with [[complex number|complex]] results, for example:
** The square root of a negative number.
** The [[logarithm]] of a negative number.
** The [[Inverse trigonometric functions|inverse sine or inverse cosine]] of a number that is less than −1 or greater than 1.

NaNs may also be explicitly assigned to variables, typically as a representation for missing values. Prior to the IEEE standard, programmers often used a special value (such as −99999999) to represent undefined or missing values, but there was no guarantee that they would be handled consistently or correctly.<ref name=idl/>

NaNs are not necessarily generated in all the above cases. If an operation can produce an exception condition and traps are not masked then the operation will cause a trap instead.<ref>{{cite web
|url=http://www.intel.com/products/processor/manuals/index.htm
|title=Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture
|date=April 2008
|pages=118–125, 266–267, 334–335
}}</ref> If an operand is a quiet NaN, and there is also no signaling NaN operand, then there is no exception condition and the result is a quiet NaN. Explicit assignments will not cause an exception even for signaling NaNs.