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using Implab.Automaton;
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using System.Diagnostics;
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using System.Runtime.CompilerServices;
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namespace Implab.Formats {
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/// <summary>
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/// Fast input scanner for max 255 states and 255 input chacters.
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/// </summary>
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/// <typeparam name="TTag"></typeparam>
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/// <remarks>
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/// <para>
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/// Creates a one rank array to store automa transition table, each entry in this table is byte, to make this table small enough to fit L1 cache.
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/// </para>
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/// <para>
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/// Each entry is addressed as <c>(state << 8) | input</c> which make this quite fast to get the next state. Each input symbol below 255 is treated as 255.
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/// </para>
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/// </remarks>
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public class FastInputScanner<TTag> {
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const int StateShift = 8;
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const int StateMask = ~((1 << StateShift) - 1);
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const int AlphabetSize = 1 << StateShift;
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const int UnclassifiedInput = (1 << StateShift) - 1;
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const byte UnreachableState = byte.MaxValue;
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readonly TTag[] m_tags;
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readonly bool[] m_final;
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readonly byte m_initialState;
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readonly byte[] m_dfa;
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int m_position;
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byte m_state;
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protected FastInputScanner(byte[] table, bool[] final, TTag[] tags, byte initial) {
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m_dfa = table;
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m_final = final;
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m_tags = tags;
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m_initialState = initial;
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}
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public FastInputScanner(int[,] dfaTable, bool[] finalStates, TTag[] tags, int initialState, int[] inputMap) {
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var states = dfaTable.GetLength(0);
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Debug.Assert(states < byte.MaxValue);
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m_dfa = new byte[states << StateShift];
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m_initialState = (byte)initialState;
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m_tags = tags;
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m_final = finalStates;
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// iterate over states
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for(int si = 0; si < states; si++) {
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// state offset for the new table
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var offset = si << StateShift;
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// iterate over alphabet
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for(int a = 0; a < AlphabetSize; a++) {
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var next = dfaTable[si, a < inputMap.Length ? inputMap[a] : AutomatonConst.UnclassifiedInput];
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if (next == AutomatonConst.UnreachableState)
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next = UnreachableState;
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m_dfa[offset | a] = (byte)next;
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}
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}
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}
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public TTag Tag {
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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get {
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return m_tags[m_state];
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}
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}
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public int Position {
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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get {
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return m_position;
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}
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}
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public bool IsFinal {
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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get {
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return m_final[m_state];
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}
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}
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public void ResetState() {
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m_state = m_initialState;
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}
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public FastInputScanner<TTag> Clone() {
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var clone = new FastInputScanner<TTag>(m_dfa, m_final, m_tags, m_initialState);
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clone.m_state = m_state;
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clone.m_position = m_position;
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return clone;
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}
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public bool Scan(char[] data, int offset, int max) {
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var next = m_state;
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m_position = offset;
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while (m_position < max) {
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var ch = data[m_position];
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next = m_dfa[(ch >= AlphabetSize ? (next << StateShift) | UnclassifiedInput : (next << StateShift) | ch)];
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if (next == UnreachableState)
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// scanner stops at the next position after the last recognized symbol
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return false;
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m_state = next;
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m_position++;
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}
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return true;
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}
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}
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}
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