Changed the way of looking up NETINFO_ITEM using net names (using boost::unordered_map). Added a hash function (wxString) for that. Introduced NETINFO_ITEM::GetNetItem( wxString ). BOARD::FindNet() uses the map.

Net codes are updated upon net list update. (BOARD::ReplaceNetlist())
Added in some places (mostly class_board.cpp) pad->SetNet() calls to synchronize net codes.
On creation of NETINFO_LIST, the first NETINFO_ITEM is added (the unconnected items net).
Removed COMPONENT_NET::m_netNumber, as it was not used anywhere.
Added an assert to D_PAD::GetNetname(), checking if net code and net name is consistent for unconnected pads. Added an assert for NETINFO_LIST::AppendNet() to assure that appended nets are unique.

It seems that at this point:
- Updating net lists works fine. The only difference between the file ouput is that after changes it contains empty nets as well.
- Nets are not saved in the lexical order. Still, net names and net codes are properly assigned to all items in the .kicad_pcb file. It is going to be addressed in the next commit. I believe it should not create any problems, as pads are sorted by their net names anyway (NETINFO_LIST::buildPadsFullList())

Performed tests:
- Created a blank PCB, saved as pic_programmer.kicad_pcb (from demos folder). Updated net lists. .kicad_pcb file (comparing to the results from master branch) differ with net order (as mentioned before), net codes and timestamps.
- Removed some of components from the above .kicad_pcb file and updated net lists. Modules reappeared. .kicad_pcb file differs in the same way as described above.
- Trying to change a pad net name (via properties dialog) results in assert being fired. It is done on purpose (as there is a call to GetNetname() and net name and net code do not match). This will not happen after the next commit.
- Prepared a simple project (starting with schematics). Imported net list, changed schematic, reimported net list - changes are applied.
- Eagle & KiCad legacy boards seem to load without any problem.

include/hashtables.h

@@ -98,6 +98,24 @@ struct fnv_1a
 };
 
 
+/// Hash function for wxString, counterpart of std::string hash
+struct WXSTRING_HASH : std::unary_function<wxString, std::size_t>
+{
+    std::size_t operator()( const wxString& aString ) const
+    {
+        std::size_t hash = 2166136261u;
+
+        for( wxString::const_iterator it = aString.begin(); it != aString.end(); ++it )
+        {
+            hash ^= (unsigned char) *it;
+            hash *= 16777619;
+        }
+
+        return hash;
+    }
+};
+
+
 /**
  * Type KEYWORD_MAP
  * is a hashtable made of a const char* and an int.  Note that use of this

pcbnew/class_board.cpp

@@ -1355,79 +1355,7 @@ NETINFO_ITEM* BOARD::FindNet( int aNetcode ) const
 
 NETINFO_ITEM* BOARD::FindNet( const wxString& aNetname ) const
 {
-    // the first valid netcode is 1.
+    return m_NetInfo.GetNetItem( aNetname );
-    // zero is reserved for "no connection" and is not used.
-    if( aNetname.IsEmpty() )
-        return NULL;
-
-    int ncount = m_NetInfo.GetNetCount();
-
-    // Search for a netname = aNetname
-#if 0
-
-    // Use a sequential search: easy to understand, but slow
-    for( int ii = 1; ii < ncount; ii++ )
-    {
-        NETINFO_ITEM* item = m_NetInfo.GetNetItem( ii );
-
-        if( item && item->GetNetname() == aNetname )
-        {
-            return item;
-        }
-    }
-
-#else
-
-    // Use a fast binary search,
-    // this is possible because Nets are alphabetically ordered in list
-    // see NETINFO_LIST::BuildListOfNets() and
-    // NETINFO_LIST::Build_Pads_Full_List()
-    int imax  = ncount - 1;
-    int index = imax;
-
-    while( ncount > 0 )
-    {
-        int ii = ncount;
-        ncount >>= 1;
-
-        if( (ii & 1) && ( ii > 1 ) )
-            ncount++;
-
-        NETINFO_ITEM* item = m_NetInfo.GetNetItem( index );
-
-        if( item == NULL )
-            return NULL;
-
-        int icmp = item->GetNetname().Cmp( aNetname );
-
-        if( icmp == 0 ) // found !
-        {
-            return item;
-        }
-
-        if( icmp < 0 ) // must search after item
-        {
-            index += ncount;
-
-            if( index > imax )
-                index = imax;
-
-            continue;
-        }
-
-        if( icmp > 0 ) // must search before item
-        {
-            index -= ncount;
-
-            if( index < 1 )
-                index = 1;
-
-            continue;
-        }
-    }
-
-#endif
-    return NULL;
 }
 
 
@@ -2618,7 +2546,10 @@ void BOARD::ReplaceNetlist( NETLIST& aNetlist, bool aDeleteSinglePadNets,
                     }
 
                     if( !aNetlist.IsDryRun() )
+                    {
                         pad->SetNetname( wxEmptyString );
+                        pad->SetNet( 0 );
+                    }
                 }
             }
             else                                 // Footprint pad has a net.
@@ -2638,7 +2569,19 @@ void BOARD::ReplaceNetlist( NETLIST& aNetlist, bool aDeleteSinglePadNets,
                     }
 
                     if( !aNetlist.IsDryRun() )
+                    {
                         pad->SetNetname( net.GetNetName() );
+
+                        NETINFO_ITEM* netinfo = FindNet( net.GetNetName() );
+                        if( netinfo == NULL )
+                        {
+                            // It is a new net, we have to add it
+                            netinfo = new NETINFO_ITEM( this, net.GetNetName(), m_NetInfo.GetNetCount() );
+                            m_NetInfo.AppendNet( netinfo );
+                        }
+
+                        pad->SetNet( netinfo->GetNet() );
+                    }
                 }
             }
         }
@@ -2711,6 +2654,7 @@ void BOARD::ReplaceNetlist( NETLIST& aNetlist, bool aDeleteSinglePadNets,
                         aReporter->Report( msg );
                     }
                     previouspad->SetNetname( wxEmptyString );
+                    previouspad->SetNet( 0 );
                 }
                 netname = pad->GetNetname();
                 count = 1;
@@ -2723,7 +2667,10 @@ void BOARD::ReplaceNetlist( NETLIST& aNetlist, bool aDeleteSinglePadNets,
 
         // Examine last pad
         if( pad && count == 1 )
+        {
             pad->SetNetname( wxEmptyString );
+            pad->SetNet( 0 );
+        }
     }
 
     // Last step: Some tests:

pcbnew/class_netinfo.h

@@ -37,6 +37,8 @@
 #include <vector>
 #include <gr_basic.h>
 #include <class_netclass.h>
+#include <boost/unordered_map.hpp>
+#include <hashtables.h>
 
 
 class wxDC;
@@ -115,7 +117,6 @@ public:
 };
 
 
-
 /**
  * Class NETINFO
  * is a container class for NETINFO_ITEM elements, which are the nets.  That makes
@@ -141,6 +142,20 @@ public:
         return m_NetBuffer[aNetcode];
     }
 
+    /**
+     * Function GetItem
+     * @param aNetName = net name to identify a given NETINFO_ITEM
+     * @return NETINFO_ITEM* - by \a aNetName, or NULL if not found
+     */
+    NETINFO_ITEM* GetNetItem( const wxString& aNetName ) const
+    {
+        NETNAMES_MAP::const_iterator result = m_netNames.find( aNetName );
+        if( result != m_netNames.end() )
+            return (*result).second;
+
+        return NULL;
+    }
+
     /**
      * Function GetNetCount
      * @return the number of nets ( always >= 1 )
@@ -188,6 +203,8 @@ public:
     void Show() const;
 #endif
 
+    typedef boost::unordered_map<const wxString, NETINFO_ITEM*, WXSTRING_HASH> NETNAMES_MAP;
+
 private:
 
     /**
@@ -214,6 +231,7 @@ private:
     void buildPadsFullList();
 
     BOARD*                      m_Parent;
+    NETNAMES_MAP m_netNames;                    ///< map for a fast look up by net names
     std::vector<NETINFO_ITEM*>  m_NetBuffer;    ///< net list (name, design constraints ..)
 
     std::vector<D_PAD*>         m_PadsFullList; ///< contains all pads, sorted by pad's netname.
@@ -394,15 +412,15 @@ public:
 
     /**
      * Function GetNetname
-     * @return const wxString * , a pointer to the full netname
+     * @return const wxString&, a reference to the full netname
      */
-    wxString GetNetname() const { return m_Netname; }
+    const wxString& GetNetname() const { return m_Netname; }
 
     /**
      * Function GetShortNetname
-     * @return const wxString * , a pointer to the short netname
+     * @return const wxString &, a reference to the short netname
      */
-    wxString GetShortNetname() const { return m_ShortNetname; }
+    const wxString& GetShortNetname() const { return m_ShortNetname; }
 
     /**
      * Function GetMsgPanelInfo

pcbnew/class_netinfolist.cpp

@@ -15,9 +15,10 @@
 
 
 // Constructor and destructor
-NETINFO_LIST::NETINFO_LIST( BOARD* aParent )
+NETINFO_LIST::NETINFO_LIST( BOARD* aParent ) : m_Parent( aParent )
 {
-    m_Parent = aParent;
+    // Make sure that the unconnected net has number 0
+    AppendNet( new NETINFO_ITEM( aParent, wxEmptyString, 0 ) );
 }
 
 
@@ -34,14 +35,20 @@ void NETINFO_LIST::clear()
 
     m_NetBuffer.clear();
     m_PadsFullList.clear();
+    m_netNames.clear();
 }
 
 
 void NETINFO_LIST::AppendNet( NETINFO_ITEM* aNewElement )
 {
+    // net names & codes are supposed to be unique
+    assert( GetNetItem( aNewElement->GetNetname() ) == NULL );
+    assert( GetNetItem( aNewElement->GetNet() ) == NULL );
+
     m_NetBuffer.push_back( aNewElement );
 
-    // D(Show();)
+    // add an entry for fast look up by a net name using a map
+    m_netNames.insert( std::make_pair( aNewElement->GetNetname(), aNewElement ) );
 }
 
 
@@ -74,18 +81,13 @@ void NETINFO_LIST::buildListOfNets()
 {
     D_PAD*          pad;
     int             nodes_count = 0;
-    NETINFO_ITEM*   net_item;
 
     // Build the PAD list, sorted by net
     buildPadsFullList();
 
     // Restore the initial state of NETINFO_ITEMs
     for( unsigned i = 0; i < GetNetCount(); ++i )
-    {
         GetNetItem( i )->Clear();
-    }
-
-    std::cout << m_PadsFullList.size() << std::endl;
 
     // Assign pads to appropriate NETINFO_ITEMs
     for( unsigned ii = 0; ii < m_PadsFullList.size(); ii++ )
@@ -95,8 +97,8 @@ void NETINFO_LIST::buildListOfNets()
         if( pad->GetNet() == 0 ) // pad not connected
             continue;
 
-        net_item = GetNetItem( pad->GetNet() );
+        // Add pad to the appropriate list of pads
-        net_item->m_PadInNetList.push_back( pad );
+        GetNetItem( pad->GetNet() )->m_PadInNetList.push_back( pad );
 
         ++nodes_count;
     }

pcbnew/class_pad.cpp

@@ -413,6 +413,7 @@ void D_PAD::CopyNetlistSettings( D_PAD* aPad )
     wxCHECK_RET( aPad != NULL && aPad != this, wxT( "Cannot copy to NULL or yourself." ) );
 
     aPad->SetNetname( GetNetname() );
+    aPad->SetNet( GetNet() );
 
     aPad->SetLocalClearance( m_LocalClearance );
     aPad->SetLocalSolderMaskMargin( m_LocalSolderMaskMargin );

pcbnew/class_pad.h

@@ -128,7 +128,13 @@ public:
      * Function GetNetname
      * @return const wxString& - the full netname
      */
-    const wxString& GetNetname() const { return m_Netname; }
+    const wxString& GetNetname() const
+    {
+        assert( ( GetNet() == 0 ) == m_Netname.IsEmpty() );
+        // assert( GetBoard()->FindNet( GetNet() ) == GetBoard()->FindNet( m_Netname ) );
+
+        return m_Netname;
+    }
 
     /**
      * Function GetShortNetname

pcbnew/pad_edition_functions.cpp

@@ -142,6 +142,7 @@ void PCB_BASE_FRAME::AddPad( MODULE* aModule, bool draw )
     // Update the pad properties.
     Import_Pad_Settings( pad, false );
     pad->SetNetname( wxEmptyString );
+    pad->SetNet( 0 );
 
     pad->SetPosition( GetCrossHairPosition() );
 

pcbnew/pcb_netlist.h

@@ -47,16 +47,14 @@ class REPORTER;
 class COMPONENT_NET
 {
     wxString m_pinName;
-    wxString m_netNumber;
     wxString m_netName;
 
 public:
     COMPONENT_NET() {}
 
-    COMPONENT_NET( const wxString& aPinName, const wxString& aNetName )
+    COMPONENT_NET( const wxString& aPinName, const wxString& aNetName ) :
+        m_pinName( aPinName ), m_netName( aNetName )
     {
-        m_pinName = aPinName;
-        m_netName = aNetName;
     }
 
     const wxString& GetPinName() const { return m_pinName; }