If an open-jaw is permissible (within or between US/Canada the smallest side of the triangle), it prices as 2 half-RTs, otherwise as 2 one-ways.
Also, most airlines will price a 3-segment circle trip as 3 half-RTs only if there is no gap, except CO, where the open-jaw is smallest mileage of the 4.
E.G.: CLE--IAH
IAH--EWR
EWR--ORD will price as 3 half RTs if all are CO flight #s, where other airlines would price 2 half RTs to & from Houston + a one-way EWR--ORD.

Double open-jaws are usually allowed only for transcontinental itins.: ORD--AMS, return CDG--MSP.