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patch to deal with prefix wrap-around

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This commit is contained in:
Jakob Rath 2024-05-15 11:34:51 +02:00
parent 343d693929
commit 865822651c
2 changed files with 43 additions and 0 deletions
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2
src/sat/smt/polysat/core.cpp
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@ -580,6 +580,8 @@ namespace polysat {
}
pdd core::subst(pdd const& p) {
if (p.is_val())
return p;
return m_assignment.apply_to(p);
}

41
src/sat/smt/polysat/viable.cpp
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@ -991,6 +991,47 @@ v0[19] := 0 v0 [-131062 ; 0[ := [-131062;0[ src ~4 <= 43691*v0;
VERIFY(!sc.is_always_false());
if (!sc.is_always_true())
deps.push_back(c.propagate(sc, c.explain_weak_eval(sc), "explain_overlap prefix evaluation"));
/*
from smtlib-2023-ni/QF_BV/sage/app5/bench_1002.smt2
v2[16] := 0 v2 [256 ; 0[ := [256;0[ src ~256 <= v2;
v2[16] := 6 v2 [0 ; v5 + 1[ := [0;6[ side-conds ~v5 + 1 == 0 src ~v2 <= v5;
v2[8] := 261 v2[8] [1536 ; 1280[ := [6;5[ deps 5 == v2 [8]@0 src
v2[16] := 0 v2 [256 ; 0[ := [256;0[ src ~256 <= v2;
consider:
v2[16] := 6 v2 [0 ; v5 + 1[ := [0;6[ side-conds ~v5 + 1 == 0 src ~v2 <= v5;
v2[8] := 261 v2[8] [1536 ; 1280[ := [6;5[ deps 5 == v2 [8]@0 src
we fix the prefix of v5+1 to 00000000
for the lower part we say (v5+1)[8] \in [6;5[, but [6;5[ has wrap-around
this will allow the wrong assignment v5 = 0.
as a patch, prevent choosing values for t after the wraparound (or before the wraparound, depending on the current value)
(this is only necessary when ebw == bw && aw == bw, because otherwise, 't' will be evaluated anyway.)
*/
if (ebw == bw && aw == bw && !(lo.is_val() && hi.is_val() && lo.val() <= (hi - 1).val())) {
// third condition: if [lo;hi[ is a value interval without wraparound, this constraint would be subsumed by the interval constraint
pdd const tt = t * rational::power_of_two(aw - abw);
pdd const tt_val = c.subst(tt);
pdd const lo_val = c.subst(lo);
VERIFY(tt_val.is_val());
VERIFY(lo_val.is_val());
signed_constraint sc;
if (lo_val.val() <= tt_val.val())
sc = cs.ule(lo, tt);
else
sc = cs.ule(tt, hi - 1);
#if DEBUG_EXPLAIN
verbose_stream() << " lo " << lo << " val " << lo_val.val() << "\n";
verbose_stream() << " hi " << hi << " val " << c.subst(hi).val() << "\n";
verbose_stream() << " 2^k' t " << tt << " val " << tt_val.val() << "\n";
verbose_stream() << " prefix no-wraparound constraint " << sc << "\n";
verbose_stream() << " eval " << sc.eval() << "\n";
verbose_stream() << " weval " << sc.weak_eval(c.get_assignment()) << "\n";
verbose_stream() << " seval " << sc.strong_eval(c.get_assignment()) << "\n";
#endif
VERIFY(!sc.is_always_false());
if (!sc.is_always_true())
deps.push_back(c.propagate(sc, c.explain_weak_eval(sc), "explain_overlap prefix no-wraparound evaluation"));
}
}
// if there is wrap-around, increment prefix