From feb04b60e04d5f533a5ee15e7b9ca2edb03eec01 Mon Sep 17 00:00:00 2001
From: Greg Landrum <greg.landrum@gmail.com>
Date: Tue, 22 Nov 2011 06:53:48 +0000
Subject: [PATCH] periodic table optimization

---
 Code/GraphMol/PeriodicTable.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/Code/GraphMol/PeriodicTable.h b/Code/GraphMol/PeriodicTable.h
index 9c5a47e8f..b46dce132 100644
--- a/Code/GraphMol/PeriodicTable.h
+++ b/Code/GraphMol/PeriodicTable.h
@@ -77,8 +77,14 @@ namespace RDKit {
     }
     //! overload
     int getAtomicNumber( const std::string &elementSymbol ) const {
-      PRECONDITION(byname.count(elementSymbol),"Element '" + elementSymbol +"' not found");
-      int anum = byname.find(elementSymbol)->second;
+      // this little optimization actually makes a measurable difference
+      // in molecule-construction time
+      int anum=-1;
+      if(elementSymbol=="C") anum=6;
+      else if(elementSymbol=="N") anum=7;
+      else if(elementSymbol=="O") anum=8;
+      else anum = byname.find(elementSymbol)->second;
+      POSTCONDITION(anum>-1,"Element '" + elementSymbol +"' not found");
       return anum;
     }