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Eliminate common suffix for simplification

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This commit is contained in:
CEisenhofer 2026-03-05 18:19:58 +01:00
parent 5a95b40bdb
commit d8871e5c1e
1 changed files with 24 additions and 6 deletions
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30
src/smt/seq/seq_nielsen.cpp
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@ -635,22 +635,22 @@ namespace seq {
continue;
}
// prefix cancellation: strip any common leading tokens.
// prefix/suffix cancellation: strip common leading and trailing tokens.
// Same char or same variable on both sides can always be cancelled.
// Two different concrete characters is a symbol clash.
{
euf::snode_vector lhs_toks, rhs_toks;
eq.m_lhs->collect_tokens(lhs_toks);
eq.m_rhs->collect_tokens(rhs_toks);
// --- prefix ---
unsigned prefix = 0;
while (prefix < lhs_toks.size() && prefix < rhs_toks.size()) {
euf::snode* lt = lhs_toks[prefix];
euf::snode* rt = rhs_toks[prefix];
if (lt->id() == rt->id() && (lt->is_char() || lt->is_var())) {
// identical token on both sides: cancel
++prefix;
} else if (lt->is_char() && rt->is_char()) {
// different concrete characters: symbol clash
m_is_general_conflict = true;
m_reason = backtrack_reason::symbol_clash;
return simplify_result::conflict;
@ -658,9 +658,27 @@ namespace seq {
break;
}
}
if (prefix > 0) {
eq.m_lhs = sg.drop_left(eq.m_lhs, prefix);
eq.m_rhs = sg.drop_left(eq.m_rhs, prefix);
// --- suffix (only among the tokens not already consumed by prefix) ---
unsigned lsz = lhs_toks.size(), rsz = rhs_toks.size();
unsigned suffix = 0;
while (suffix < lsz - prefix && suffix < rsz - prefix) {
euf::snode* lt = lhs_toks[lsz - 1 - suffix];
euf::snode* rt = rhs_toks[rsz - 1 - suffix];
if (lt->id() == rt->id() && (lt->is_char() || lt->is_var())) {
++suffix;
} else if (lt->is_char() && rt->is_char()) {
m_is_general_conflict = true;
m_reason = backtrack_reason::symbol_clash;
return simplify_result::conflict;
} else {
break;
}
}
if (prefix > 0 || suffix > 0) {
eq.m_lhs = sg.drop_left(sg.drop_right(eq.m_lhs, suffix), prefix);
eq.m_rhs = sg.drop_left(sg.drop_right(eq.m_rhs, suffix), prefix);
changed = true;
}
}