Does it help to add an argument to the pscan function for reversing sequence scanning?

[GlassyWing]

Some tasks need to reverse scan sequences, but a flip -> scan->flip operation too slow.

[GlassyWing]

Alright, it seems that a very simple implementation approach is:

class PScanReverse:

    @staticmethod
    def pscan(A, X):
        # call reverse version of PScan
        return PScan.pscan_rev(A, X)

    @staticmethod
    def pscan_rev(A, X):
        # call reverse version of PScan
        return PScan.pscan(A, X)

    def forward(...)
        # same of `PScan.forward` but make some sequential adjustments
        ...
        
    def backward(...)
       # same of `PScan.backward` but make some sequential adjustments
        ...