Back to the README.

@arki/math/rounding

One vocabulary everywhere — Decimal, Rational, the float helpers, and formatting all take the same RoundingMode:

Mode	Meaning	2.5 →	−2.5 →
up	away from zero	3	−3
down	toward zero	2	−2
ceiling	toward +∞	3	−2
floor	toward −∞	2	−3
halfUp	nearest, ties away from zero (school rounding)	3	−3
halfDown	nearest, ties toward zero	2	−2
halfEven	nearest, ties to even (banker's rounding)	2	−2
unnecessary	throw RoundingNecessaryError if digits are lost	—	—

Defaults follow intent: display-shaped calls (round, roundTo, Decimal.round, toFixed, formatting) default to halfUp, which is what people expect to see. Precision-shaped calls (dividedBy, toScale, toDecimal) default to unnecessary, so precision is never lost without you asking.

Note that JavaScript's own Math.round(-2.5) is -2 (ties toward +∞) — none of the modes above, and one of the reasons this package exists.