[ktpsns]

Adding two rationals boils down to adding 2x two integers. Integer arithmetic is in general less complex then floating point arithmetic. But of course that's not true if your hardware supports single instruction double floating point arithmetic (which any relevant 64bit architecture does).

[munrocket]

The problems begins when calculations is long and int64/int32 not enough to store full fraction precision. Lol seems that I find a bug in Fraction.js in rounding https://runkit.com/munrocket/fraction-js-test, but it used in popular Math.js library.