PartitionBlock MkNewBlock()
{
PartitionBlock blk = new PartitionBlock(dfsa.MaxSym);
allBlocks.Add(blk);
return(blk);
}
/// <summary>
/// Move the node with value dSt from this partition to blk.
/// </summary>
/// <param name="dSt">value to be moved</param>
/// <param name="blk">destination partition</param>
internal void MoveMember(DFSA.DState dSt, PartitionBlock blk)
{
// Assert: dSt must belong to LinkedList this.members
LinkedListNode <DFSA.DState> node = dSt.listNode;
this.members.Remove(node);
this.predCount--;
blk.AddNode(node);
}
/// <summary>
/// Maps old dfsa states to new states in the minimized set.
/// </summary>
/// <param name="dSt">The state to be mapped</param>
/// <returns>The replacement state</returns>
internal static DFSA.DState PMap(DFSA.DState dSt)
{
PartitionBlock blk = dSt.block as PartitionBlock;
if (blk.MemberCount == 1)
{
return(dSt);
}
else
{
return(blk.FirstMember);
}
}
/// <summary>
/// The initial partitions are formed by the following
/// rules:
/// Every accept state shares a partition with all other
/// accept states that have the same semantic action.
/// All other states go in the partition "otherStates".
///
/// Addendum, Version 0.3: start states must be kept out
/// of the otherStates partition, otherwise prefixes can
/// be chopped off by, for example, concluding that states
/// {1,3} are equivalent in the following FSA. They are,
/// but the computation of yytext is broken if you merge!
///
/// a b c d
/// (start state) 1---->2---->3---->4-----(5) (accept state)
///
/// c d
/// (start state) 1---->7---->(5) (accept state)
///
/// The inverse transition function is computed at the same
/// time as the initial partition is performed.
/// </summary>
/// <param name="list">The list of all DStates</param>
internal void PopulatePartitions(List <DFSA.DState> list)
{
PartitionBlock blk = null;
dfsa.origLength = list.Count;
for (int i = 1; i < list.Count; i++)
{
DFSA.DState dSt = list[i];
if (dSt.accept != null)
{
blk = FindPartition(dSt);
}
else if (dSt.isStart)
{
blk = startStates;
}
else
{
blk = otherStates;
}
blk.AddState(dSt);
dSt.block = blk;
// now create the inverse transition function
for (int j = 0; j < dfsa.MaxSym; j++)
{
DFSA.DState pred = dSt.GetNext(j);
if (pred != null)
{
pred.AddPredecessor(dSt, j);
}
}
}
// Now add the eofState as an accept state.
// This is *despite* the state not having an accept reference!
blk = MkNewBlock();
acceptStates.Add(blk);
blk.AddState(list[0]);
list[0].block = blk;
// And now finally initialize the pair list.
worklist.Push(startStates);
worklist.Push(otherStates); // EXPERIMENTAL
foreach (PartitionBlock lst in acceptStates)
{
worklist.Push(lst);
}
}
/// <summary>
/// Find an existing partition block with which dSt is compatible,
/// or construct a new partition into which dSt can be placed.
/// </summary>
/// <param name="dSt"></param>
/// <returns></returns>
PartitionBlock FindPartition(DFSA.DState dSt)
{
foreach (PartitionBlock blk in acceptStates)
{
// Assert every partition in acceptStates has at least one member.
// Assert every member has the same semantic action.
//
// This would be a simple matter except for right context. Is such
// cases the action is an input backup, then the user action. For a
// pattern R1/R2 the regex R1.R2 (concatenation) is recognized
// and the buffer backed up to the position of the '/'.
// In the case of R1 of fixed length N we do "yyless(N);"
// In the case of R2 of fixed length N we do "yyless(yyleng-N);"
// If the first state in the partition has both lengths fixed
// we must choose one or the other backup action, and only add
// other states that are compatible with that choice.
DFSA.DState first = blk.FirstMember;
if (DFSA.SpansEqual(first.accept.aSpan, dSt.accept.aSpan))
{
if (!first.HasRightContext && !dSt.HasRightContext)
{
return(blk);
}
else
{
if (first.lhCntx > 0 && first.lhCntx == dSt.lhCntx)
// From now on only add states with matching lhs length
{
first.rhCntx = 0; dSt.rhCntx = 0; return(blk);
}
if (first.rhCntx > 0 && first.rhCntx == dSt.rhCntx)
// From now on only add states with matching rhs length
{
first.lhCntx = 0; dSt.lhCntx = 0; return(blk);
}
}
}
}
PartitionBlock nxt = MkNewBlock();
acceptStates.Add(nxt);
return(nxt);
}
internal Minimizer(DFSA dfsa)
{
this.dfsa = dfsa;
otherStates = MkNewBlock();
startStates = MkNewBlock();
}
/// <summary>
/// Refine the partitions by splitting incompatible states
/// </summary>
internal void RefinePartitions()
{
int generation = 0;
while (worklist.Count > 0)
{
List <DFSA.DState> predSet = null;
//
// We are going to split all blocks with respect to a
// particular (Block, Symbol) pair.
// Fetch the pair components.
//
// In order to avoid having to reset the predCount ints
// all the time we keep a generation count to indicate to
// which pass through the loop the counts apply.
//
PartitionBlock blk = worklist.Peek();
int sym = blk.Sym - 1;
if (sym < 0)
{
worklist.Pop(); // Remove block from the worklist.
continue; // Go around again to get new block.
}
generation++;
predSet = new List <DFSA.DState>();
//
// Form a set of all those states that have a
// next-state in "blk" on symbol "sym".
// Note that despite the nested loops the
// complexity is only N == number of states.
//
foreach (DFSA.DState dSt in blk.members)
{
if (dSt.HasPredecessors())
{
List <DFSA.DState> prds = dSt.GetPredecessors(sym);
if (prds != null && prds.Count > 0)
{
foreach (DFSA.DState pSt in prds)
{
// The same predecessor state might appear on the
// list for more than one state of the blk.members.
// States should only appear once in the predSet "set"
if (pSt.listOrd != generation) // This predecessor is not in the set already
{
PartitionBlock predBlk = (pSt.block as PartitionBlock);
pSt.listOrd = generation;
if (predBlk.Gen != generation)
{
predBlk.Gen = generation;
predBlk.PredCount = 0;
}
predSet.Add(pSt); // Add the predecessor to the set
predBlk.PredCount++;
}
}
}
}
}
blk.Sym--; // "Remove" (blk,sym) from the pair list.
//
// Now, if the predecessor set is not empty,
// we split all blocks with respect to (blk,sym)
//
if (predSet.Count != 0)
{
List <PartitionBlock> splits = new List <PartitionBlock>();
foreach (DFSA.DState lSt in predSet)
{
PartitionBlock tBlk = null;
PartitionBlock lBlk = (lSt.block as PartitionBlock);
if (lBlk.PredCount != lBlk.MemberCount) // Need to split this block
{
tBlk = lBlk.twinBlk;
if (tBlk == null)
{
tBlk = MkNewBlock();
splits.Add(tBlk);
lBlk.twinBlk = tBlk;
tBlk.twinBlk = lBlk;
}
lBlk.MoveMember(lSt, tBlk);
lSt.block = tBlk;
}
}
foreach (PartitionBlock tBlk in splits)
{
PartitionBlock lBlk = tBlk.twinBlk;
PartitionBlock push = null;
if (lBlk.Sym == 0) // lBlk is not currently on the list so push smaller block
{
if (lBlk.MemberCount < tBlk.MemberCount)
{
push = lBlk;
}
else
{
push = tBlk;
}
}
else // lBlk is on the list with Sym > 0
{
push = tBlk;
if (lBlk.MemberCount < tBlk.MemberCount)
{
// tBlk has the larger cardinality, so give it the smaller Sym value
tBlk.Sym = lBlk.Sym;
lBlk.Sym = dfsa.MaxSym;
}
}
worklist.Push(push);
lBlk.twinBlk = null;
tBlk.twinBlk = null;
}
}
} // end of while loop...
}
