To make the transformation work, I have to represent a set of
intervals on each edge, not just a single interval. Because no two intervals
overlap, I can use a wonderful dirty trick, detailed below.
I also may convert a node's name string to a namearray
mapping
field values to strings. The goal is for children of the same
parent to share a single name array; that way the edges can be merged and
the name operator can be implemented with an array reference.
If I don't convert a node's name, the only penalty is that the tree
might be bigger.
(Code generation will be different for the two cases.)
Now, the dirty representation trick: I can represent a set of numbers S (a union of intervals) as two sets, lo and hi, such that
addinterval
adds a new interval to such a set S,
relying on the fact that no two intervals overlap.
<*>= [D->] procedure addinterval(loset, hiset, lonum, hinum) if member(loset, hinum) then delete(loset, hinum) else insert(hiset, hinum) if member(hiset, lonum) then delete(hiset, lonum) else insert(loset, lonum) return end
Definesaddinterval
(links are to index).
To convert trees to dags I need to be able to compare two nodes for structural identity, and the easiest way is to compute a canonical representation as a string:
node : [fname:patimage(list of edges)]
| <NOMATCH>
| (image(node.name):image(node.cs.arms[1].original))
edge : patimage(list of sort(loset ++ hiset)):node
<*>+= [<-D->] procedure nodetostring(n, depth) static cache initial cache := table() /depth := 0 if /cache[n] then if *n.children > 0 then { result := "[" || n.field.name || ":" every result ||:= edgetostring(!n.children, depth+2) cache[n] := result || "]" } else if *n.cs.arms = 0 then cache[n] := "<NOMATCH>" else cache[n] := "(" || image(n.name) || ":" || image(n.cs.arms[1].original) ||")" return \cache[n] end procedure edgetostring(e,depth) return left("\n", depth) || "{" || patimage(sort(e.lo ++ e.hi)) || ":" || nodetostring(e.node,depth) || "}" end
Definesedgetostring
,nodetostring
(links are to index).
Conversion to dag is the usual bottom-up hashing; here I compute the
string and then use the string to index into a table.
The real work of merging edges is done by combinechildren
.
If edge merging results in a single each, the node is replaced by
its child, provided the edge really covers all possible values
of the field.
<*>+= [<-D->] procedure tree2dag(n, nodetable, depth) /nodetable := table() /depth := 0 if *n.children > 0 then combinechildren(n, nodetable, depth+2) # converts edges to set form if *n.children = 1 then { e := n.children[1] if covers(n.children[1], n.field.hi - n.field.lo) then n := n.children[1].node # all roads to child: hoist it else warning("node with one child doesn't match all cases") } s := nodetostring(n, depth) /nodetable[s] := n return nodetable[s] end
Definestree2dag
(links are to index).
Here's where I check coverage.
Only success or failure of covers
is meaningful, not
the value returned.
<*>+= [<-D->] procedure covers(e, width) l := sort(e.lo ++ e.hi) return *l = 2 & l[1] = 0 & l[2] = 2^width end
Definescovers
(links are to index).
The complicated stuff here is identifying a name array. At each node, either all edges go in an exiting name array or a new name array is used. If not, I create a new one.
<*>+= [<-D->] record namearray(field, tbl, hi, codename) # field used as index, table[integer] of name, bound on table, name of this array global natable
Definesnamearray
,natable
(links are to index).
<*>+= [<-D->] procedure arraycandidates(n) initial MAXRANGE := 32 suspend e := !n.children & type(e.node.name) == "string" & e.hi - e.lo <= MAXRANGE & e end procedure combinechildren(n, nodetable, depth) initial natable := table() if arraycandidates(n).node.name ~== arraycandidates(n).node.name then { <change names of children from strings to namearrays when possible> } lotable := table() hitable := table() every e := !n.children & child := tree2dag(e.node, nodetable, depth) do { /lotable[child] := set() /hitable[child] := set() addinterval(lotable[child], hitable[child], e.lo, e.hi) } n.children := [] every child := key(lotable) do put(n.children, edge(child, lotable[child], hitable[child])) return end
Definesarraycandidates
,combinechildren
(links are to index).
<change names of children from strings to namearrays when possible>= (<-U) mightuse := set() # name arrays we might use must have right field every na := !\natable[n.field] do insert(mightuse, na) every e := arraycandidates(n) & na := !mightuse do if \na.tbl[e.lo to e.hi - 1] ~== e.node.name then # slot used with wrong name delete(mightuse, na) if *mightuse > 0 then willuse := ?mightuse else { /natable[n.field] := set() insert(natable[n.field], willuse := namearray(n.field, table(), 0)) } every e := arraycandidates(n) & e.lo - willuse.hi <= MAXRANGE do { every willuse.tbl[e.lo to e.hi - 1] := e.node.name; e.node.name := willuse willuse.hi <:= e.hi }
<*>+= [<-D] procedure namesused(n, result) /result := set() if type(n.name) == "namearray" then insert(result, n.name) every namesused((!n.children).node, result) return result end
Definesnamesused
(links are to index).