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fix #3951

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2020-04-14 10:51:16 -07:00
parent 5e0c34cae2
commit 5f81913292
2 changed files with 39 additions and 19 deletions
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43
src/tactic/core/reduce_invertible_tactic.cpp
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@ -25,6 +25,7 @@ Notes:
#include "ast/ast_pp.h"
#include "ast/rewriter/expr_safe_replace.h"
#include "ast/rewriter/rewriter_def.h"
#include "ast/rewriter/th_rewriter.h"
#include "tactic/tactic.h"
#include "tactic/core/reduce_invertible_tactic.h"
#include "tactic/core/collect_occs.h"
@ -306,6 +307,11 @@ private:
}
if (!rest) return false;
// so far just support numeral
rational r;
if (!m_bv.is_numeral(rest, r))
return false;
// create case split on
// divisbility of 2
// v * t ->
@ -318,31 +324,30 @@ private:
// to reproduce the original v from t
// solve for v*t = extract[sz-1:i](v') ++ zero[i-1:0]
// using values for t and v'
// thus
//
// udiv(extract[sz-1:i](v') ++ zero[i-1:0], t)
// thus let t' = t / 2^i
// and t'' = the multiplicative inverse of t'
// then t'' * v' * t = t'' * v' * t' * 2^i = v' * 2^i = extract[sz-1:i](v') ++ zero[i-1:0]
// so t'' *v' works
//
// TBD: this argument is flawed. Unit test breaks with either
// the above or udiv(v, t)
unsigned sz = m_bv.get_bv_size(p);
expr_ref bit1(m_bv.mk_numeral(1, 1), m);
new_v = m_bv.mk_numeral(0, sz);
for (unsigned i = sz; i-- > 0; ) {
expr_ref extr_i(m_bv.mk_extract(i, i, rest), m);
expr_ref cond(m.mk_eq(extr_i, bit1), m);
expr_ref part(v, m);
if (i > 0) {
part = m_bv.mk_concat(m_bv.mk_extract(sz-1, i, v), m_bv.mk_numeral(0, i));
}
new_v = m.mk_ite(cond, part, new_v);
unsigned sh = 0;
while (r.is_pos() && r.is_even()) {
r /= rational(2);
++sh;
}
if (mc) {
if (r.is_pos() && sh > 0) {
new_v = m_bv.mk_concat(m_bv.mk_extract(sz-1, sh, v), m_bv.mk_numeral(0, sh));
}
if (mc && !r.is_zero()) {
ensure_mc(mc);
expr_ref div(m), def(m);
div = m.mk_app(m_bv.get_fid(), OP_BUDIV_I, v, rest);
def = m_bv.mk_numeral(0, sz);
def = m.mk_ite(m.mk_eq(def, rest), def, div);
expr_ref def(m);
rational inv_r;
VERIFY(m_bv.mult_inverse(r, sz, inv_r));
def = m_bv.mk_bv_mul(m_bv.mk_numeral(inv_r, sz), v);
(*mc)->add(v, def);
TRACE("invertible_tactic", tout << def << "\n";);
}