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Use length information during Nielsen saturation

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CEisenhofer 2026-03-12 17:01:44 +01:00
parent e8354a783a
commit 3ad9c290fc
4 changed files with 321 additions and 3 deletions
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28
src/smt/nseq_model.cpp
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@ -233,8 +233,34 @@ namespace smt {
if (exp_val.is_one())
return base_val;
// For small exponents, concatenate directly
// For small exponents, concatenate directly; for large ones,
// build a concrete string constant to avoid enormous AST chains
// that cause cleanup_expr to diverge.
unsigned n_val = exp_val.get_unsigned();
constexpr unsigned POWER_EXPAND_LIMIT = 1000;
if (n_val > POWER_EXPAND_LIMIT) {
// Try to extract a concrete character from the base (seq.unit(c))
// and build a string literal directly (O(1) AST node).
unsigned ch = 0;
expr* unit_arg = nullptr;
if (m_seq.str.is_unit(base_val, unit_arg) && m_seq.is_const_char(unit_arg, ch)) {
svector<unsigned> buf(n_val, ch);
zstring result(buf.size(), buf.data());
return expr_ref(m_seq.str.mk_string(result), m);
}
// Also handle if base is already a string constant
zstring base_str;
if (m_seq.str.is_string(base_val, base_str) && base_str.length() > 0) {
svector<unsigned> buf;
for (unsigned i = 0; i < n_val; ++i)
for (unsigned j = 0; j < base_str.length(); ++j)
buf.push_back(base_str[j]);
zstring result(buf.size(), buf.data());
return expr_ref(m_seq.str.mk_string(result), m);
}
// Fallback: cap exponent to avoid divergence
n_val = POWER_EXPAND_LIMIT;
}
expr_ref acc(base_val);
for (unsigned i = 1; i < n_val; ++i)
acc = m_seq.str.mk_concat(acc, base_val);