These two routines generate a run value, using the run index pair in $C837-$C838. For Xform_Run_a the scalar value is passed in the A register, while for Xform_Run, the scalar value must already be in $C83B. The transformed value is return in the A register.
DP = $C8
A-reg = length for rise/run (Xform_Rise_a only)
A-reg = run value