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new xor simplification

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Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
This commit is contained in:
Leonardo de Moura 2012-10-26 14:57:06 -07:00
parent c15275b53b
commit c5540c7de9
1 changed files with 45 additions and 0 deletions
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45
src/ast/rewriter/bv_rewriter.cpp
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@ -1410,6 +1410,51 @@ br_status bv_rewriter::mk_bv_xor(unsigned num, expr * const * args, expr_ref & r
}
}
}
// XOR is a mask
// All arguments but one is a numeral.
//
// Apply a transformation of the form:
//
// (bvxor a 0011) --> (concat ((_ extract 3 2) a) ((_ extract 1 0) (bvnot a)))
//
if (!v1.is_zero() && num_coeffs == num - 1) {
// find argument that is not a numeral
expr * t = 0;
for (unsigned i = 0; i < num; i++) {
t = args[i];
if (!is_numeral(t))
break;
}
SASSERT(t != 0);
numeral two(2);
expr_ref_buffer exs(m());
expr_ref not_t(m());
not_t = m_util.mk_bv_not(t);
unsigned low = 0;
unsigned i = 0;
while (i < sz) {
while (i < sz && mod(v1, two).is_one()) {
i++;
div(v1, two, v1);
}
if (i != low) {
exs.push_back(m_mk_extract(i-1, low, not_t));
low = i;
}
while (i < sz && mod(v1, two).is_zero()) {
i++;
div(v1, two, v1);
}
if (i != low) {
exs.push_back(m_mk_extract(i-1, low, t));
low = i;
}
}
std::reverse(exs.c_ptr(), exs.c_ptr() + exs.size());
result = m_util.mk_concat(exs.size(), exs.c_ptr());
return BR_REWRITE3;
}
if (!merged && !flattened && (num_coeffs == 0 || (num_coeffs == 1 && !v1.is_zero() && v1 != (m_util.power_of_two(sz) - numeral(1)))))
return BR_FAILED;