A quiet NaN or qNaN in the IEEE 754-2008 standard (referred to as IEEE 754 henceforth) is a NaN which is quiet
in the sense of rarely signaling a floating-point exception. This is in contrast
to the signaling NaN (sNaN) which often occurs in
conjunction with any number of exceptions and handling mechanisms defined therefor
(IEEE Computer Society 2008).
Within the framework documentation, it is suggested that qNaNs be implemented in such a way as to afford useful diagnostic information regarding invalid or unavailable
data and results. Under the default exception handling mechanisms provided within
IEEE 754, any operation which signals an invalid operation exception and for
which a floating-point result is expected shall return a quiet NaN; operations not
delivering a floating-point result, such as comparisons, can instead signal an invalid-operation
exception when a NaN is an input. This concerns the treatment of NaN inputs rather
than returning a NaN as a non-floating-point result.
Goldberg, D. "What Every Computer Scientist Should Know About Floating-Point Arithmetic." ACM Comput. Surv.23, 5-48,
1991. https://doi.org/10.1145/103162.103163.IEEE
Computer Society. "IEEE Standard for Floating-Point Arithmetic: IEEE Std 754-2008
(Revision of IEEE Std 754-1985)." 2008. https://doi.org/10.1109/IEEESTD.2008.4610935.
