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tl: add some simplifications for first_match

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Following a discussion with Victor Khomenko.

* doc/tl/tl.tex: Document those rules.
* spot/tl/simplify.cc: Implement them.
* tests/core/reduccmp.test: Test them.
This commit is contained in:
Alexandre Duret-Lutz 2019-05-08 15:05:47 +02:00
parent b7cd475632
commit c6605e951d
3 changed files with 73 additions and 20 deletions
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53
spot/tl/simplify.cc
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@ -856,7 +856,6 @@ namespace spot
case op::ap:
case op::Not:
case op::FStar:
case op::first_match:
return f;
case op::X:
{
@ -1429,6 +1428,58 @@ namespace spot
}
return formula::Star(h, min, f.max());
}
case op::first_match:
{
formula h = f[0];
if (h.is(op::Star))
{
// first_match(b[*i..j]) = b[*i]
// first_match(f[*i..j]) = first_match(f[*i])
unsigned m = h.min();
formula s = formula::Star(h[0], m, m);
return h[0].is_boolean() ? s : formula::first_match(s);
}
else if (h.is(op::Concat))
{
// If b is Boolean and e accepts [*0], we have
// first_match(b;f) = b;first_match(f)
// first_match(f;e) = first_match(f)
// first_match(f;g[*i..j]) = first_match(f;g[*i])
// the first two rules can be repeated, so we will loop
// to save the recursion and intermediate caching.
// Extract Boolean formulas at the beginning.
int i = 0;
int n = h.size();
while (i < n && h[i].is_boolean())
++i;
vec prefix;
prefix.reserve(i + 1); // +1 to append first_match()
for (int ii = 0; ii < i; ++ii)
prefix.push_back(h[ii]);
// Extract suffix, minus trailing formulas that accept [*0].
// "i" is the start of the suffix.
do
--n;
while (i <= n && h[n].accepts_eword());
vec suffix;
suffix.reserve(n + 1 - i);
for (int ii = i; ii <= n; ++ii)
suffix.push_back(h[ii]);
if (!suffix.empty() && suffix.back().is(op::Star))
{
formula s = suffix.back();
unsigned smin = s.min();
suffix.back() = formula::Star(s[0], smin, smin);
}
prefix.push_back(formula::first_match
(formula::Concat(suffix)));
formula res = formula::Concat(prefix);
if (res != f)
return recurse(res);
}
return f;
}
}
SPOT_UNREACHABLE();
}