Jan Burse, created Aug 17. 2019
* We provide a couple of additional bitwise operations. The evaluable
* functions bitcount/1, bitlength/1 and lowestsetbit/1 deal with the
* determination of certain bits of the given integer. The implementation
* is more efficient than would be possible with existing logical,
* shift and test operations.
* bitlength(333) --> 9
* The evaluable functions setbit/2 and clearbit/2 update the given
* integer in a more efficient way than would be possible with existing
* logical and shift operations. The predicate testbit/2 tests a
* particular bit in a given integer, again the implementation is more
* efficient than would be possible with existing logical, shift and
* test operations.
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* bitcount(X, N):
* Predicate succeeds in N with the number of non-zero bits of X.
* bitlength(X, N):
* Predicate succeeds in N with the highest non-zero bit of X.
bitlength/2, 'SupplementBits', 1).
* lowestsetbit(X, N):
* Predicate succeeds in N with the lowest non-zero bit of X.
lowestsetbit/2, 'SupplementBits', 2).
* setbit(X, Y, Z):
* The predicate succeeds in Z with Y \/ (1 << X).
* clearbit(X, Y, Z):
* The predicate succeeds in Z with Y /\ \ (1 << X).
* testbit(X, Y):
* The predicate succeeds when Y /\ (1 << X) =\= 0.