/// <summary>
/// Initializes the GSS
/// </summary>
public GSS()
{
nodeLabels = new BigList <int>();
nodeGenerations = new BigList <GSSGeneration>();
edges = new BigList <GSSEdge>();
edgeGenerations = new BigList <GSSGeneration>();
generation = -1;
path0 = new GSSPath();
paths0 = new [] { path0 };
paths = new GSSPath[INIT_PATHS_COUNT];
}
/// <summary>
/// Prepares for the forthcoming reduction operations
/// </summary>
/// <param name="first">The first label</param>
/// <param name="path">The path being reduced</param>
/// <param name="length">The reduction length</param>
public void ReductionPrepare(int first, GSSPath path, int length)
{
// build the stack
if (length > 0)
{
for (int i = 0; i < length - 1; i++)
{
stack[i] = path[length - 2 - i];
}
stack[length - 1] = first;
}
// initialize the reduction data
cacheNext = 0;
handleNext = 0;
popCount = 0;
}
/// <summary>
/// Setups a reusable GSS path with the given length
/// </summary>
/// <param name="index">The index in the buffer of reusable paths</param>
/// <param name="last">The last GLR state in the path</param>
/// <param name="length">The path's length</param>
private void SetupPath(int index, int last, int length)
{
if (index >= paths.Length)
{
Array.Resize(ref paths, paths.Length + INIT_PATHS_COUNT);
}
if (paths[index] == null)
{
paths[index] = new GSSPath(length);
}
else
{
paths[index].Ensure(length);
}
paths[index].Last = last;
paths[index].Generation = GetGenerationOf(last);
}
/// <summary>
/// Builds the SPPF
/// </summary>
/// <param name="generation">The current GSS generation</param>
/// <param name="production">The LR production</param>
/// <param name="first">The first label of the path</param>
/// <param name="path">The reduction path</param>
/// <returns>The identifier of the corresponding SPPF node</returns>
private int BuildSPPF(int generation, LRProduction production, int first, GSSPath path)
{
Symbol variable = symVariables[production.Head];
sppf.ReductionPrepare(first, path, production.ReductionLength);
for (int i = 0; i != production.BytecodeLength; i++)
{
LROpCode op = production[i];
switch (op.Base)
{
case LROpCodeBase.SemanticAction:
{
SemanticAction action = symActions[production[i + 1].DataValue];
i++;
action.Invoke(variable, sppf);
break;
}
case LROpCodeBase.AddVirtual:
{
int index = production[i + 1].DataValue;
sppf.ReductionAddVirtual(index, op.TreeAction);
i++;
break;
}
case LROpCodeBase.AddNullVariable:
{
int index = production[i + 1].DataValue;
sppf.ReductionAddNullable(nullables[index], op.TreeAction);
i++;
break;
}
default:
sppf.ReductionPop(op.TreeAction);
break;
}
}
return(sppf.Reduce(generation, production.Head, production.HeadAction));
}
/// <summary>
/// Copy the content of another path to this one
/// </summary>
/// <param name="path">The path to copy</param>
/// <param name="length">The path's length</param>
public void CopyLabelsFrom(GSSPath path, int length)
{
Array.Copy(path.labels, labels, length);
}
/// <summary>
/// Gets all paths in the GSS starting at the given node and with the given length
/// </summary>
/// <param name="from">The starting node</param>
/// <param name="length">The length of the requested paths</param>
/// <param name="count">The number of paths</param>
/// <returns>A collection of paths in this GSS</returns>
public GSSPath[] GetPaths(int from, int length, out int count)
{
if (length == 0)
{
// use the common 0-length GSS path to avoid new memory allocation
path0.Last = from;
count = 1;
return(paths0);
}
// Initializes the first path
SetupPath(0, from, length);
// The number of paths in the list
int total = 1;
// For the remaining hops
for (int i = 0; i != length; i++)
{
int m = 0; // Insertion index for the compaction process
int next = total; // Insertion index for new paths
for (int p = 0; p != total; p++)
{
int last = paths[p].Last;
int genIndex = paths[p].Generation;
// Look for new additional paths from last
GSSGeneration gen = edgeGenerations[genIndex];
int firstEdgeTarget = -1;
int firstEdgeLabel = -1;
for (int e = gen.Start; e != gen.Start + gen.Count; e++)
{
GSSEdge edge = edges[e];
if (edge.From == last)
{
if (firstEdgeTarget == -1)
{
// This is the first edge
firstEdgeTarget = edge.To;
firstEdgeLabel = edge.Label;
}
else
{
// Not the first edge
// Clone and extend the new path
SetupPath(next, edge.To, length);
paths[next].CopyLabelsFrom(paths[p], i);
paths[next][i] = edge.Label;
// Go to next insert
next++;
}
}
}
// Check whether there was at least one edge
if (firstEdgeTarget != -1)
{
// Continue the current path
if (m != p)
{
GSSPath t = paths[m];
paths[m] = paths[p];
paths[p] = t;
}
paths[m].Last = firstEdgeTarget;
paths[m].Generation = GetGenerationOf(firstEdgeTarget);
paths[m][i] = firstEdgeLabel;
// goto next
m++;
}
}
if (m != total)
{
// if some previous paths have been removed
// => compact the list if needed
for (int p = total; p != next; p++)
{
GSSPath t = paths[m];
paths[m] = paths[p];
paths[p] = t;
m++;
}
// m is now the exact number of paths
total = m;
}
else if (next != total)
{
// no path has been removed, but some have been added
// => next is the exact number of paths
total = next;
}
}
count = total;
return(paths);
}
/// <summary>
/// Executes a reduction operation for a given path
/// </summary>
/// <param name="generation">The current GSS generation</param>
/// <param name="reduction">The reduction operation</param>
/// <param name="path">The GSS path to use for the reduction</param>
private void ExecuteReduction(int generation, Reduction reduction, GSSPath path)
{
// Get the rule's head
Symbol head = symVariables[reduction.prod.Head];
// Resolve the sub-root
int label = sppf.GetLabelFor(path.Generation, new TableElemRef(TableType.Variable, reduction.prod.Head));
if (label == SPPF.EPSILON)
{
// not in history, build the SPPF here
label = BuildSPPF(generation, reduction.prod, reduction.first, path);
}
// Get the target state by transition on the rule's head
int to = GetNextByVar(gss.GetRepresentedState(path.Last), head.ID);
// Find a node for the target state in the GSS
int w = gss.FindNode(generation, to);
if (w != -1)
{
// A node for the target state is already in the GSS
if (!gss.HasEdge(generation, w, path.Last))
{
// But the new edge does not exist
gss.CreateEdge(w, path.Last, label);
// Look for the new reductions at this state
if (reduction.prod.ReductionLength != 0)
{
int count = parserAutomaton.GetActionsCount(to, nextToken.TerminalID);
for (int i = 0; i != count; i++)
{
LRAction action = parserAutomaton.GetAction(to, nextToken.TerminalID, i);
if (action.Code == LRActionCode.Reduce)
{
LRProduction prod = parserAutomaton.GetProduction(action.Data);
// length 0 reduction are not considered here because they already exist at this point
if (prod.ReductionLength != 0)
{
reductions.Enqueue(new Reduction(path.Last, prod, label));
}
}
}
}
}
}
else
{
// Create the new corresponding node in the GSS
w = gss.CreateNode(to);
gss.CreateEdge(w, path.Last, label);
// Look for all the reductions and shifts at this state
int count = parserAutomaton.GetActionsCount(to, nextToken.TerminalID);
for (int i = 0; i != count; i++)
{
LRAction action = parserAutomaton.GetAction(to, nextToken.TerminalID, i);
if (action.Code == LRActionCode.Shift)
{
shifts.Enqueue(new Shift(w, action.Data));
}
else if (action.Code == LRActionCode.Reduce)
{
LRProduction prod = parserAutomaton.GetProduction(action.Data);
if (prod.ReductionLength == 0)
{
reductions.Enqueue(new Reduction(w, prod, SPPF.EPSILON));
}
else if (reduction.prod.ReductionLength != 0)
{
reductions.Enqueue(new Reduction(path.Last, prod, label));
}
}
}
}
}
/// <summary>
/// Checks whether the specified terminal is indeed expected for a reduction
/// </summary>
/// <param name="gssNode">The GSS node from which to reduce</param>
/// <param name="terminal">The terminal to check</param>
/// <returns><code>true</code> if the terminal is really expected</returns>
/// <remarks>
/// This check is required because in the case of a base LALR graph,
/// some terminals expected for reduction in the automaton are coming from other paths.
/// </remarks>
private bool CheckIsExpected(int gssNode, Symbol terminal)
{
// queue of GLR states to inspect:
List <int> queueGSSHead = new List <int>(); // the related GSS head
List <int[]> queueVStack = new List <int[]>(); // the virtual stack
// first reduction
{
int count = parserAutomaton.GetActionsCount(gss.GetRepresentedState(gssNode), terminal.ID);
for (int j = 0; j != count; j++)
{
LRAction action = parserAutomaton.GetAction(gss.GetRepresentedState(gssNode), terminal.ID, j);
if (action.Code == LRActionCode.Reduce)
{
// execute the reduction
LRProduction production = parserAutomaton.GetProduction(action.Data);
int nbPaths;
GSSPath[] paths = gss.GetPaths(gssNode, production.ReductionLength, out nbPaths);
for (int k = 0; k != nbPaths; k++)
{
GSSPath path = paths[k];
// get the target GLR state
int next = GetNextByVar(gss.GetRepresentedState(path.Last), symVariables[production.Head].ID);
// enqueue the info, top GSS stack node and target GLR state
queueGSSHead.Add(path.Last);
queueVStack.Add(new[] { next });
}
}
}
}
// now, close the queue
for (int i = 0; i != queueGSSHead.Count; i++)
{
int head = queueVStack[i][queueVStack[i].Length - 1];
int count = parserAutomaton.GetActionsCount(head, terminal.ID);
if (count == 0)
{
continue;
}
for (int j = 0; j != count; j++)
{
LRAction action = parserAutomaton.GetAction(head, terminal.ID, j);
if (action.Code == LRActionCode.Shift)
{
// yep, the terminal was expected
return(true);
}
if (action.Code == LRActionCode.Reduce)
{
// execute the reduction
LRProduction production = parserAutomaton.GetProduction(action.Data);
if (production.ReductionLength == 0)
{
// 0-length reduction => start from the current head
int[] virtualStack = new int[queueVStack[i].Length + 1];
Array.Copy(queueVStack[i], virtualStack, queueVStack[i].Length);
virtualStack[virtualStack.Length - 1] = GetNextByVar(head, symVariables[production.Head].ID);
// enqueue
queueGSSHead.Add(queueGSSHead[i]);
queueVStack.Add(virtualStack);
}
else if (production.ReductionLength < queueVStack[i].Length)
{
// we are still the virtual stack
int[] virtualStack = new int[queueVStack[i].Length - production.ReductionLength + 1];
Array.Copy(queueVStack[i], virtualStack, virtualStack.Length - 1);
virtualStack[virtualStack.Length - 1] = GetNextByVar(virtualStack[virtualStack.Length - 2], symVariables[production.Head].ID);
// enqueue
queueGSSHead.Add(queueGSSHead[i]);
queueVStack.Add(virtualStack);
}
else
{
// we reach the GSS
int nbPaths;
GSSPath[] paths = gss.GetPaths(queueGSSHead[i], production.ReductionLength - queueVStack[i].Length, out nbPaths);
for (int k = 0; k != nbPaths; k++)
{
GSSPath path = paths[k];
// get the target GLR state
int next = GetNextByVar(gss.GetRepresentedState(path.Last), symVariables[production.Head].ID);
// enqueue the info, top GSS stack node and target GLR state
queueGSSHead.Add(path.Last);
queueVStack.Add(new[] { next });
}
}
}
}
}
// nope, that was a pathological case in a LALR graph
return(false);
}
/// <summary>
/// Gets the priority of the specified context required by the specified terminal
/// The priority is a positive integer. The lesser the value the higher the priority.
/// A value of -1 represents the unavailability of the required context.
/// </summary>
/// <param name="context">A context</param>
/// <param name="onTerminalID">The identifier of the terminal requiring the context</param>
/// <returns>The context priority, or -1 if the context is unavailable</returns>
public int GetContextPriority(int context, int onTerminalID)
{
// the default context is always active
if (context == Automaton.DEFAULT_CONTEXT)
{
return(int.MaxValue);
}
if (lexer.tokens.Size == 0)
{
// this is the first token, does it open the context?
return(parserAutomaton.GetContexts(0).Opens(onTerminalID, context) ? 0 : -1);
}
// try to only look at stack heads that expect the terminal
List <int> queue = new List <int>();
List <LRProduction> productions = new List <LRProduction>();
List <int> distances = new List <int>();
bool foundOnPreviousShift = false;
foreach (Shift shift in shifts)
{
int count = parserAutomaton.GetActionsCount(shift.to, onTerminalID);
if (count == 0)
{
continue;
}
for (int i = 0; i != count; i++)
{
LRAction action = parserAutomaton.GetAction(shift.to, onTerminalID, i);
if (action.Code == LRActionCode.Shift)
{
// does the context opens with the terminal?
if (parserAutomaton.GetContexts(shift.to).Opens(onTerminalID, context))
{
return(0);
}
// looking at the immediate history, does the context opens from the shift just before?
if (parserAutomaton.GetContexts(gss.GetRepresentedState(shift.from)).Opens(nextToken.TerminalID, context))
{
foundOnPreviousShift = true;
break;
}
// no, enqueue
if (!queue.Contains(shift.from))
{
queue.Add(shift.from);
productions.Add(null);
distances.Add(2);
}
}
else
{
// this is reduction
LRProduction production = parserAutomaton.GetProduction(action.Data);
// looking at the immediate history, does the context opens from the shift just before?
if (parserAutomaton.GetContexts(gss.GetRepresentedState(shift.from)).Opens(nextToken.TerminalID, context))
{
if (production.ReductionLength < 1)
{
// the reduction does not close the context
foundOnPreviousShift = true;
break;
}
}
// no, enqueue
if (!queue.Contains(shift.from))
{
queue.Add(shift.from);
productions.Add(production);
distances.Add(2);
}
}
}
}
if (foundOnPreviousShift)
{
// found the context opening on the previous shift (and was not immediately closed by a reduction)
return(1);
}
if (queue.Count == 0)
{
// the track is empty, the terminal is unexpected
return(-1);
}
// explore the current GSS to find the specified context
for (int i = 0; i != queue.Count; i++)
{
int count;
GSSPath[] paths = gss.GetPaths(queue[i], 1, out count);
for (int p = 0; p != count; p++)
{
int from = paths[p].Last;
int symbolID = sppf.GetSymbolOn(paths[p][0]).ID;
int distance = distances[i];
LRProduction production = productions[i];
// was the context opened on this transition?
if (parserAutomaton.GetContexts(gss.GetRepresentedState(from)).Opens(symbolID, context))
{
if (production == null || production.ReductionLength < distance)
{
return(distance);
}
}
// no, enqueue
if (!queue.Contains(from))
{
queue.Add(from);
productions.Add(production);
distances.Add(distance + 1);
}
}
}
// at this point, the requested context is not yet open
// can it be open by a token with the specified terminal ID?
// queue of GLR states to inspect:
List <int> queueGSSHead = new List <int>(); // the related GSS head
List <int[]> queueVStack = new List <int[]>(); // the virtual stack
// first reduction
foreach (Shift shift in shifts)
{
int count = parserAutomaton.GetActionsCount(shift.to, onTerminalID);
if (count > 0)
{
// enqueue the info, top GSS stack node and target GLR state
queueGSSHead.Add(shift.from);
queueVStack.Add(new[] { shift.to });
}
}
// now, close the queue
for (int i = 0; i != queueGSSHead.Count; i++)
{
int head = queueVStack[i][queueVStack[i].Length - 1];
int count = parserAutomaton.GetActionsCount(head, onTerminalID);
if (count == 0)
{
continue;
}
for (int j = 0; j != count; j++)
{
LRAction action = parserAutomaton.GetAction(head, onTerminalID, j);
if (action.Code != LRActionCode.Reduce)
{
continue;
}
// execute the reduction
LRProduction production = parserAutomaton.GetProduction(action.Data);
if (production.ReductionLength == 0)
{
// 0-length reduction => start from the current head
int[] virtualStack = new int[queueVStack[i].Length + 1];
Array.Copy(queueVStack[i], virtualStack, queueVStack[i].Length);
int next = GetNextByVar(head, symVariables[production.Head].ID);
virtualStack[virtualStack.Length - 1] = next;
// enqueue
queueGSSHead.Add(queueGSSHead[i]);
queueVStack.Add(virtualStack);
}
else if (production.ReductionLength < queueVStack[i].Length)
{
// we are still the virtual stack
int[] virtualStack = new int[queueVStack[i].Length - production.ReductionLength + 1];
Array.Copy(queueVStack[i], virtualStack, virtualStack.Length - 1);
int next = GetNextByVar(virtualStack[virtualStack.Length - 2], symVariables[production.Head].ID);
virtualStack[virtualStack.Length - 1] = next;
// enqueue
queueGSSHead.Add(queueGSSHead[i]);
queueVStack.Add(virtualStack);
}
else
{
// we reach the GSS
int nbPaths;
GSSPath[] paths = gss.GetPaths(queueGSSHead[i], production.ReductionLength - queueVStack[i].Length, out nbPaths);
for (int k = 0; k != nbPaths; k++)
{
GSSPath path = paths[k];
// get the target GLR state
int next = GetNextByVar(gss.GetRepresentedState(path.Last), symVariables[production.Head].ID);
// enqueue the info, top GSS stack node and target GLR state
queueGSSHead.Add(path.Last);
queueVStack.Add(new[] { next });
}
}
}
}
foreach (int[] vstack in queueVStack)
{
int state = vstack[vstack.Length - 1];
int count = parserAutomaton.GetActionsCount(state, onTerminalID);
for (int i = 0; i != count; i++)
{
LRAction action = parserAutomaton.GetAction(state, onTerminalID, i);
if (action.Code == LRActionCode.Shift && parserAutomaton.GetContexts(state).Opens(onTerminalID, context))
{
// the context opens here
return(0);
}
}
}
// the context is still unavailable
return(-1);
}
