From 9e2b2e2abb3c2693db29c23b7a7706a1700e1f1b Mon Sep 17 00:00:00 2001
From: Justin Balthrop <justin@geni.com>
Date: Fri, 7 Aug 2009 14:43:40 -0700
Subject: [PATCH] optimized compare_absolute method

---
 lib/bdb/simple.rb   | 56 +++++++++++++++++++++++++++------------------
 test/simple_test.rb |  2 +-
 2 files changed, 35 insertions(+), 23 deletions(-)

diff --git a/lib/bdb/simple.rb b/lib/bdb/simple.rb
index 4bfb4df..ba75ae8 100644
--- a/lib/bdb/simple.rb
+++ b/lib/bdb/simple.rb
@@ -68,37 +68,49 @@ class Bdb::Simple
     @db = nil
   end
 
+  CLASS_ORDER = {}
+  [FalseClass, TrueClass, Fixnum, Numeric, Float, Symbol, String, Array].each_with_index {|c, i| CLASS_ORDER[c] = i}
+
   def self.compare_absolute(left, right)
-    if left.class == right.class
-      if left.is_a?(Array) and right.is_a?(Array)
+    if left.is_a?(right.class)
+      case left
+      when Array
         # Arrays: compare one element at a time.
-        left.zip(right) do |l,r|
-          comp = compare_absolute(l, r)
-          return comp unless comp == 0
+        n = [left.size, right.size].min
+        n.times do |i|
+          comp = compare_absolute(left[i], right[i])
+          return comp if comp != 0
         end
-        left.size == right.size ? 0 : -1
-      elsif left.is_a?(Hash) and right.is_a?(Hash)
-        # Hashes: sort the keys and compare as an array of arrays.
+        left.size <=> right.size
+      when Hash
+        # Hashes: sort the keys and compare as an array of arrays. This may be slow.
         left  = left.to_a.sort  {|a,b| compare_absolute(a[0],b[0])}
         right = right.to_a.sort {|a,b| compare_absolute(a[0],b[0])}
         compare_absolute(left, right)
+      when NilClass, TrueClass, FalseClass
+        0
+      when Symbol
+        left.to_s <=> right.to_s
       else
-        begin
-          # Try to use the spaceship operator.
-          left <=> right
-        rescue NoMethodError => e
-          left.hash <=> right.hash
-        end
-      end
+        # Use the spaceship operator.
+        left <=> right
+      end    
+    elsif left.kind_of?(Numeric) and right.kind_of?(Numeric)
+      # Numerics are always comparable.
+      left <=> right
     else
-      # Nil is the smallest. Hash is the largest. All other objects are sorted by class name.
-      return -1 if left.is_a?(NilClass)
-      return  1 if right.is_a?(NilClass)
-      return  1 if left.is_a?(Hash)
-      return -1 if right.is_a?(Hash)
+      # Nil is the smallest. Hash is the largest.
+      return -1 if left.is_a?(NilClass) or right.is_a?(Hash)
+      return  1 if left.is_a?(Hash)     or right.is_a?(NilClass)
       
-      # Compare class names and hashes as a last resort if that fails.
-      right.class.name <=> left.class.name
+      # Try to use the class sort order so we don't have to do a string comparison.
+      left_order  = CLASS_ORDER[left.class]
+      right_order = CLASS_ORDER[right.class]
+      if left_order.nil? and right_order.nil?
+        left.class.name <=> right.class.name
+      else
+        (left_order || 9999) <=> (right_order || 9999)
+      end
     end
   end
 end
diff --git a/test/simple_test.rb b/test/simple_test.rb
index 67c5eb1..809283d 100644
--- a/test/simple_test.rb
+++ b/test/simple_test.rb
@@ -44,7 +44,7 @@ class SimpleTest < Test::Unit::TestCase
   def test_compare_absolute
     list = [5, 6, "foo", :bar, "bar", :foo, [1,2,4], true, [1,2,3], false, [1], [2], nil, {}, {:b => 1, :a => 1}, {:b => 2, :a => 1}]
 
-    expected = [nil, true, :bar, :foo, "bar", "foo", 5, 6, false, [1], [1, 2, 3], [1, 2, 4], [2], {}, {:a=>1, :b=>1}, {:a=>1, :b=>2}]
+    expected = [nil, false, true, 5, 6, :bar, :foo, "bar", "foo", [1], [1, 2, 3], [1, 2, 4], [2], {}, {:a=>1, :b=>1}, {:a=>1, :b=>2}]
     assert_equal expected, list.sort {|a,b| Bdb::Simple.compare_absolute(a,b)}
     100.times do
       assert_equal expected, list.shuffle.sort {|a,b| Bdb::Simple.compare_absolute(a,b)}