Prune redundant nodes in the trie.

Signed-off-by: Staffan Gimåker <staffan@spotify.com>

src/trie.cpp

 /*
     Copyright (c) 2009-2011 250bpm s.r.o.
     Copyright (c) 2007-2009 iMatix Corporation
+    Copyright (c) 2011-2012 Spotify AB
     Copyright (c) 2007-2011 Other contributors as noted in the AUTHORS file
 
     This file is part of 0MQ.
@@ -35,7 +36,8 @@
 zmq::trie_t::trie_t () :
     refcnt (0),
     min (0),
-    count (0)
+    count (0),
+    live_nodes (0)
 {
 }
 
@@ -113,6 +115,7 @@ bool zmq::trie_t::add (unsigned char *prefix_, size_t size_)
         if (!next.node) {
             next.node = new (std::nothrow) trie_t;
             zmq_assert (next.node);
+            ++live_nodes;
         }
         return next.node->add (prefix_ + 1, size_ - 1);
     }
@@ -120,6 +123,7 @@ bool zmq::trie_t::add (unsigned char *prefix_, size_t size_)
         if (!next.table [c - min]) {
             next.table [c - min] = new (std::nothrow) trie_t;
             zmq_assert (next.table [c - min]);
+            ++live_nodes;
         }
         return next.table [c - min]->add (prefix_ + 1, size_ - 1);
     }
@@ -146,7 +150,18 @@ bool zmq::trie_t::rm (unsigned char *prefix_, size_t size_)
      if (!next_node)
          return false;
 
-     return next_node->rm (prefix_ + 1, size_ - 1);
+     bool ret = next_node->rm (prefix_ + 1, size_ - 1);
+
+     if (next_node->is_redundant ()) {
+         delete next_node;
+         if (count == 1)
+             next.node = 0;
+         else
+             next.table [c - min] = 0;
+         --live_nodes;
+     }
+
+     return ret;
 }
 
 bool zmq::trie_t::check (unsigned char *data_, size_t size_)
@@ -227,3 +242,7 @@ void zmq::trie_t::apply_helper (
     }
 }
 
+bool zmq::trie_t::is_redundant() const
+{
+    return refcnt == 0 && live_nodes == 0;
+}

src/trie.hpp

 /*
     Copyright (c) 2009-2011 250bpm s.r.o.
     Copyright (c) 2007-2009 iMatix Corporation
+    Copyright (c) 2011-2012 Spotify AB
     Copyright (c) 2007-2011 Other contributors as noted in the AUTHORS file
 
     This file is part of 0MQ.
@@ -57,10 +58,12 @@ namespace zmq
             unsigned char **buff_, size_t buffsize_, size_t maxbuffsize_,
             void (*func_) (unsigned char *data_, size_t size_, void *arg_),
             void *arg_);
+        bool is_redundant () const;
 
         uint32_t refcnt;
         unsigned char min;
         unsigned short count;
+        unsigned short live_nodes;
         union {
             class trie_t *node;
             class trie_t **table;