Here is the story of Check():

JLP wanted to use also for BSGS this Check() function but finally he gave up as Rand() is always returning 0  (zero)
as it was not working also command line switch -check is not implemented so you can not call this Check() function
because Rand() is not used for algorithmus in no way JLP left it unresolved for BSGS 

but for Kangaroo 2.2 125bit the story is different:
the Rand() is used also for algorithmus so JLP must had solved this problem and he did (so far I have not found what was corrected/changed)
now the whole Check() function works properly even for both k1 and r1 curves (different curve-p parameters affecting all mod operations)

b.SetBase16("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F");        k1
b.SetBase16("FFFFFFFF00000001000000000000000000000000FFFFFFFFFFFFFFFFFFFFFFFF");        r1


PS: I hope NotATether will find some day a bit of free time and willingness to forget existing Kangaroo256 code and
instead take JLP Kangaroo 125bit and extend it to the 254bit without any additional changes
(no DP change, no Div() and others optimizations....)

I believe this would be the easiest way, do you agree NAT ?