/// <summary>
/// 填充 DFA 的数据。
/// </summary>
/// <param name="grammar">词法分析器使用的语法。</param>
/// <param name="useTrailing">是否用到了向前看。</param>
private void FillDfa(Grammar <T> grammar, out bool useTrailing)
{
// 构造 DFA。
Nfa nfa = BuildNfa(grammar, out useTrailing);
int headCnt = this.contextCount * 2;
Dfa dfa = nfa.BuildDfa(headCnt);
dfa.Minimize(headCnt);
// 获取 DFA 的数据。
this.charClass = dfa.CharClass.GetCharClassMap();
this.stateCount = dfa.Count;
this.states = new StateData[stateCount];
this.charClassCount = dfa.CharClass.Count;
for (int i = 0; i < this.stateCount; i++)
{
DfaState state = dfa[i];
int[] transitions = new int[charClassCount];
for (int j = 0; j < charClassCount; j++)
{
DfaState target = state[j];
if (target == null)
{
transitions[j] = Constants.DeadState;
}
else
{
transitions[j] = target.Index;
}
}
states[i] = new StateData(transitions, state.SymbolIndex);
}
}
/// <summary>
/// 初始化 <see cref="DfaState"/> 类的新实例。
/// </summary>
/// <param name="dfa">状态所在的 DFA。</param>
/// <param name="index">状态的索引。</param>
public DfaState(Dfa dfa, int index)
{
this.Dfa = dfa;
this.Index = index;
this.transitions = new DfaState[dfa.CharClass.Count];
}
/// <summary>
/// 根据当前的 NFA 构造 DFA，采用子集构造法。
/// </summary>
/// <param name="headCnt">头节点的个数。</param>
internal Dfa BuildDfa(int headCnt)
{
Dfa dfa = new Dfa(charClass);
// DFA 和 NFA 的状态映射表，DFA 的一个状态对应 NFA 的一个状态集合。
Dictionary <DfaState, HashSet <NfaState> > stateMap =
new Dictionary <DfaState, HashSet <NfaState> >();
// 由 NFA 状态集合到对应的 DFA 状态的映射表（与上表互逆）。
Dictionary <HashSet <NfaState>, DfaState> dfaStateMap =
new Dictionary <HashSet <NfaState>, DfaState>(SetEqualityComparer <NfaState> .Default);
Stack <DfaState> stack = new Stack <DfaState>();
// 添加头节点。
for (int i = 0; i < headCnt; i++)
{
DfaState head = dfa.NewState();
head.SymbolIndex = new int[0];
HashSet <NfaState> headStates = EpsilonClosure(Enumerable.Repeat(this[i], 1));
stateMap.Add(head, headStates);
dfaStateMap.Add(headStates, head);
stack.Push(head);
}
int charClassCnt = charClass.Count;
while (stack.Count > 0)
{
DfaState state = stack.Pop();
HashSet <NfaState> stateSet = stateMap[state];
// 遍历字符类。
for (int i = 0; i < charClassCnt; i++)
{
// 对于 NFA 中的每个转移，寻找 Move 集合。
HashSet <NfaState> set = Move(stateSet, i);
if (set.Count > 0)
{
set = EpsilonClosure(set);
DfaState newState;
if (!dfaStateMap.TryGetValue(set, out newState))
{
// 添加新状态.
newState = dfa.NewState();
stateMap.Add(newState, set);
dfaStateMap.Add(set, newState);
stack.Push(newState);
// 合并符号索引。
newState.SymbolIndex = set.Where(s => s.SymbolIndex != Constants.None)
.Select(s =>
{
if (s.StateType == NfaStateType.TrailingHead)
{
return(int.MaxValue - s.SymbolIndex);
}
else
{
return(s.SymbolIndex);
}
}).OrderBy(idx => idx).ToArray();
}
// 添加 DFA 的转移。
state[i] = newState;
}
}
}
return(dfa);
}
