.

wcfs/δbtail.go

@@ -20,6 +20,55 @@
 package main
 // XXX -> Package xbtree complements package lab.nexedi.com/kirr/neo/go/zodb/btree.
 // TODO move -> btree when ΔTail matures.
+// XXX doc
+
+// δ(BTree) notes
+// ==============
+//
+// input: BTree, (@new, []oid)  ->  find out δ(BTree) i.e. {-k(v), +k'(v'), ...}
+//
+// - oid ∈ Bucket
+// - oid ∈ BTree
+//
+// Bucket:
+//
+//      old = {k  -> v}
+//      new = {k' -> v'}
+//
+//      Δ = -k(v), +k(v), ...
+//
+// => for all buckets
+//
+//      Δ accumulates to []δk(v)[n+,n-]  n+ ∈ {0,1}, n- ∈ {0,1}, if n+=n- - cancel
+//
+//
+// BTree:
+//
+//      old = {k  -> B}   or {k  -> T}
+//      new = {k' -> B'}  or {k' -> T'}
+//
+//      Δ = -k(B), +k(B), -k(T), +K(T), ...
+//
+// we translate (in top-down order):
+//
+//      k(B) -> {} of k(v)
+//      k(T) -> {} of k(B) -> {} of k(v)
+//
+// which gives
+//
+//      Δ = k(v), +k(v), ...
+//
+// i.e. exactly as for buckets and it accumulates to global Δ.
+//
+// The globally-accumulated Δ is the answer for δ(BTree, (@new, []oid))
+//
+// top-down order is obtained via toposort({oid}) wrt visited PathSet.
+//
+// δ(BTree) in wcfs context:
+//
+// . -k(blk) -> invalidate #blk
+// . +k(blk) -> invalidate #blk (e.g. if blk was previously read as hole)
+
 
 //go:generate ./gen-set main Oid   Oid zset_oid.go
 
@@ -976,53 +1025,6 @@ func (δBtail *ΔBtail) SliceByRootRev(root *Tree, lo, hi zodb.Tid) /*readonly*/
 	panic("TODO")
 }
 
-// δ(BTree) notes
-// ==============
-//
-// input: BTree, (@new, []oid)  ->  find out δ(BTree) i.e. {-k(v), +k'(v'), ...}
-//
-// - oid ∈ Bucket
-// - oid ∈ BTree
-//
-// Bucket:
-//
-//      old = {k  -> v}
-//      new = {k' -> v'}
-//
-//      Δ = -k(v), +k(v), ...
-//
-// => for all buckets
-//
-//      Δ accumulates to []δk(v)[n+,n-]  n+ ∈ {0,1}, n- ∈ {0,1}, if n+=n- - cancel
-//
-//
-// BTree:
-//
-//      old = {k  -> B}   or {k  -> T}
-//      new = {k' -> B'}  or {k' -> T'}
-//
-//      Δ = -k(B), +k(B), -k(T), +K(T), ...
-//
-// we translate (in top-down order):
-//
-//      k(B) -> {} of k(v)
-//      k(T) -> {} of k(B) -> {} of k(v)
-//
-// which gives
-//
-//      Δ = k(v), +k(v), ...
-//
-// i.e. exactly as for buckets and it accumulates to global Δ.
-//
-// The globally-accumulated Δ is the answer for δ(BTree, (@new, []oid))
-//
-// top-down order is obtained via toposort({oid}) wrt visited PathSet.
-//
-// δ(BTree) in wcfs context:
-//
-// . -k(blk) -> invalidate #blk
-// . +k(blk) -> invalidate #blk (e.g. if blk was previously read as hole)
-
 
 // ---- misc ----