The ceil, floor, llround, lround, round, and trunc functions round in predetermined directions, whereas llrint, lrint, and rint round according to the current (dynamic) rounding mode. For more information on controlling the dynamic rounding mode, see fenv(3) and fesetround(3).

Unlike the algebraic functions listed earlier, the routines in this section may not produce a result that is correctly rounded, so reproducible results cannot be guaranteed across platforms. For most of these functions, however, incorrect rounding occurs rarely, and then only in very-close-to-halfway cases.