some +6/-6 circuits

But back on topic:
adding +6 to a number for BCD correction.

And here a neat +6 schematic, drawn from the
info gathered out of the 100181 datasheet:

Warning:
For input values greater than 9,
this schematic won't work !

The next page discusses the 100181,
so I felt a need to mention said schematic here.

If you want to add 6 to the full range of numbers
from 0..15, the problem obviously is generating B3'.

A schematic derived from this table:

A different implementation of the schematic above:

To make the set complete:
adding -6 to a number:
(or subtracting +6)

...Had to "invent" my own solution.
The Q2' signal:

The Q3' signal:

And now my schematic for subtracting 6 from a number:

...Of course, the circuitry for generating Q3'
looks a little bit complicated.

When building 100181 styled BCD arithmetic,
you only have to subtract 6 from a set of numbers
from 6..15, and in that case, you could simplify
the schematic above for generating Q3' pretty much:

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