z3py - Check overflow with Z3 -

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i'm new z3 , checking online python tutorial.

then thought check overflow behavior in bitvecs.

i wrote code:

x = bitvec('x', 3) y = int('y')  solve(bv2int(x) == y, not(bv2int(x + 1) == (y + 1)))

and expecting [y = 7, x = 7] (i.e. when values equal successors not because x + 1 0 , y + 1 8)

but z3 answers [y = 0, x = 0].

what doing wrong?

i don't think you're doing wrong, looks bv2int buggy:

 x = bitvec('x', 3)  prove(x <= 3)  prove(bv2int(x) <= 3)

z3py proves first one, gives counter-example x=0 second. doesn't sound right. (the explanation might weird python thing, don't see how.)

also note model depend on whether + treats bit-vector signed number in python bindings, believe case. however, bv2int might not so, treating unsigned value. further complicate matters.

in case, looks bv2int not quite kosher; i'd stay away until there's official answer z3 folks.


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