getInterval() weird behaviour

[zero0cool0]

IOS: 15.1 on a real device
XCode: 13.1
SwiftDate: 6.3.1 - installed via CocoaPods

Trying to understand the exact behaviour of getInterval() to calculate the difference in calendar days between two DateInRegion instances.
How come

       let d1 = "2021-12-04T12:00:00+01:00".toDate()!
       let d2 = "2021-12-05T06:00:00+01:00".toDate()!
       debugPrint(d1.getInterval(toDate: d2, component: .day))

outputs 1, which is what I would expect, but

      let d1 = "2021-12-04T12:00:00+01:00".toDate()!
      let d2 = "2021-12-05T00:00:00+01:00".toDate()!
      debugPrint(d1.getInterval(toDate: d2, component: .day))

outputs 0 which is unexpected, as clearly, d2 is one day after d1 ?

[mhmdzaid]

it's a half day (12 h) difference based on the hours in the date @zero0cool0