Complicated If Then / V Lookup / Match Statement

I need a formula that would be able to calculate the distance from the start
of a code to the end of a code. An example table is below. The start and
end of a code is indicated in the CONT. column. (Start of first code = S1,
end of first Code = F1, Start of second code = S2, end of second Code = F2,
etc.) Maybe a table could be used (E1:F2) that shows the corresponding Start
& Finish Codes. Two conditions need to be met before the length (in DIST
column) is to be calculated, the Report numbers and the Codes must be the
same for both rows.

ABCDEF
1S1S2
2REPORTDIST.CONT.CODEF1F2
31005S1B
410010S2A
510012F1B
610014C
710016F2A
82002B
92004S1B
1020010F2B

In the table above:
- Code B in report 100 would go for a distance of 7 (12-5).
- Code A in report 100 would go for a distance of 6 (16-10).
- Code B in report 200 would go for a distance of 6 (10-4).