Added comments.

diff --git a/re2c/src/ir/dfa/minimization.cc b/re2c/src/ir/dfa/minimization.cc
index 8b6cc03903a5e2ac4fc4e4283745e51b1f87f125..b15714c2e8a5d11e0a45a9219bf6937bb2e344c2 100644 (file)
--- a/re2c/src/ir/dfa/minimization.cc
+++ b/re2c/src/ir/dfa/minimization.cc
@@ -40,6 +40,7 @@ static void minimization_table(
                tbl[i + 1] = tbl[i] + i;
        }
 
+       // see note [distinguish states by contexts]
        for (size_t i = 0; i < count; ++i)
        {
                dfa_state_t *s1 = states[i];
@@ -83,6 +84,19 @@ static void minimization_table(
                }
        }
 
+       // Equivalence relation defined by the matrix is transitive
+       // by construction. Thus we can simply find the first state
+       // which is not distinguishable from current and choose it as a
+       // representative: all other states with the same representative
+       // have to be equivalent to current state due to transitivity.
+       //
+       // The only requirement is to deterministically choose the
+       // representative: e.g. always choose the one with the lowest
+       // index.
+       //
+       // Note that transitivity is crucial: without it the problem
+       // would be equivalent to the clique cover problem.
+
        for (size_t i = 0; i < count; ++i)
        {
                part[i] = i;
@@ -120,6 +134,7 @@ static void minimization_moore(
 
        size_t *next = new size_t[count];
 
+       // see note [distinguish states by contexts]
        std::map<std::pair<const RuleInfo*, bool>, size_t> init;
        for (size_t i = 0; i < count; ++i)
        {
@@ -197,6 +212,15 @@ static void minimization_moore(
        delete[] next;
 }
 
+/* note [distinguish states by contexts]
+ *
+ * States that differ only in context set must still be distinguished
+ * otherwise contexts that start with iteration  will be broken, e.g.:
+ *     "" / "b"* {}
+ * because first iteration will be merged with other iterations
+ * causing context being saved on each iteration.
+ */
+
 void minimization(dfa_t &dfa)
 {
        const size_t count = dfa.states.size();