Rounding — floor / ceiling / round / truncate

Round to integers or a precision, with the half-way rule Rakudo uses.

Four routines turn a fractional number into a whole one: floor (down), ceiling (up), truncate (toward zero), and round (to nearest).

floor, ceiling, truncate #

say 3.7.floor;
say 3.2.ceiling;
say 3.7.truncate;
say (-3.7).floor;

3
4
3
-4

floor goes toward −∞, ceiling toward +∞, truncate toward zero (so (-3.7).truncate is -3, while (-3.7).floor is -4).

round to a precision #

round takes an optional scale — round to the nearest multiple of it.

say 3.5.round;
say 3.14159.round(0.01);

4
3.14

Halves round toward +∞ #

For a value exactly halfway, round rounds toward +∞ — so a positive .5 goes up and a negative .5 goes toward zero.

say 3.5.round;
say (-3.5).round;
say (-2.5).round;

4
-3
-2

3.5 rounds up to 4; -3.5 rounds up to -3 (not -4).

Notes #

• The half-way rule only matters for values ending exactly in .5; every other value rounds to the genuinely nearest integer.
• floor, ceiling, and truncate have no half-way ambiguity.
• .Int on a fractional number truncates toward zero — the same as .truncate.