The nearbyint functions round their argument to an integer value in
floating point format, using the current rounding direction and without
raising the inexact exception.
The rint functions do the same, but will raise the inexact
exception when the result differs in value from the argument.
SUSv2 and POSIX 1003.1-2001 contain text about overflow (which might set
errno to ERANGE, or raise an exception). In practice, the result cannot
overflow on any current machine, so this error-handling stuff is just
nonsense. (More precisely, overflow can happen only when the maximum value of
the exponent is smaller than the number of mantissa bits. For the IEEE-754
standard 32-bit and 64-bit floating point numbers the maximum value of the
exponent is 128 (resp. 1024), and the number of mantissa bits is 24 (resp.