From 4190b720dc6efed49c8454a517b43404dd65313e Mon Sep 17 00:00:00 2001
From: Todd Gruben <tgruben@umbel.com>
Date: Mon, 28 Jul 2014 19:22:48 +0000
Subject: [PATCH] performance enhancement for Difference

---
 index/bitmap.go       | 17 +++++++++++++++--
 index/storage_test.go |  4 ++--
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/index/bitmap.go b/index/bitmap.go
index 881c50a6e..b4210f353 100644
--- a/index/bitmap.go
+++ b/index/bitmap.go
@@ -121,6 +121,14 @@ func BlockArray_intersection(a *BlockArray, b *BlockArray) BlockArray {
 	return o
 }
 
+func BlockArray_difference(a *BlockArray, b *BlockArray) BlockArray {
+	var o = BlockArray{}
+	for i, _ := range a.Block {
+		o.Block[i] = a.Block[i] &^ b.Block[i]
+	}
+	return o
+}
+
 func (s *BlockArray) set_bit(BlockIndex uint8, bit uint8) bool {
 	val := s.Block[BlockIndex] & (1 << bit)
 	s.Block[BlockIndex] |= 1 << bit
@@ -295,9 +303,14 @@ func Difference(a_bm IBitmap, b_bm IBitmap) IBitmap {
 			b = b.Next()
 		} else if a.Item().Key == b.Item().Key {
 			var a_node = a.Item()
-			var b_node = BlockArray_invert(&b.Item().Value) //probably need to copy this out
-			var o = BlockArray_intersection(&a_node.Value, &b_node)
+			//var b_node = BlockArray_invert(&b.Item().Value) //probably need to copy this out
+			//var o = BlockArray_intersection(&a_node.Value, &b_node)
+
+			var b_node = b.Item().Value
+			var o = BlockArray_difference(&a_node.Value, &b_node)
+
 			var o_node = &Chunk{a_node.Key, o}
+
 			//could not add if all zero
 			if o_node.Value.bitcount() > 0 {
 				output.AddChunk(o_node)
diff --git a/index/storage_test.go b/index/storage_test.go
index 9a1d00e11..69dd22b3a 100644
--- a/index/storage_test.go
+++ b/index/storage_test.go
@@ -6,7 +6,7 @@ import (
 
 	//	"io/ioutil"
 	//   "time"
-	"github.com/davecgh/go-spew/spew"
+
 	. "github.com/smartystreets/goconvey/convey"
 )
 
@@ -58,7 +58,7 @@ func TestStorage(t *testing.T) {
 
 		fmt.Println("FETCH")
 		bm, _ := storage.Fetch(bitmap_id, db, frame, slice)
-		spew.Dump(bm)
+		//spew.Dump(bm)
 		SetBit(bm, 0)
 		SetBit(bm, 1)
 		SetBit(bm, 2)