From 0572790504b1939fe5cab2976dd8531aca315c8b Mon Sep 17 00:00:00 2001
From: Daniel Lemire <lemire@gmail.com>
Date: Fri, 16 Apr 2021 15:24:29 -0400
Subject: [PATCH 1/3] This should reduce bound checks in a function.

---
 setutil_generic.go | 36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/setutil_generic.go b/setutil_generic.go
index 9edcc902..3668f800 100644
--- a/setutil_generic.go
+++ b/setutil_generic.go
@@ -2,10 +2,13 @@
 
 package roaring
 
+
 func union2by2(set1 []uint16, set2 []uint16, buffer []uint16) int {
-	pos := 0
-	k1 := 0
-	k2 := 0
+	pos := uint(0)
+	k1 := uint(0)
+	k2 := uint(0)
+	len1 := uint(len(set1))
+	len2 := uint(len(set2))
 	if 0 == len(set2) {
 		buffer = buffer[:len(set1)]
 		copy(buffer, set1[:])
@@ -20,29 +23,34 @@ func union2by2(set1 []uint16, set2 []uint16, buffer []uint16) int {
 	s2 := set2[k2]
 	buffer = buffer[:cap(buffer)]
 	for {
+		if pos >= uint(len(buffer)) {
+			panic("You provided a buffer with insufficient capacity")
+		}
 		if s1 < s2 {
 			buffer[pos] = s1
 			pos++
 			k1++
-			if k1 >= len(set1) {
+			if k1 >= len1 {
 				copy(buffer[pos:], set2[k2:])
-				pos += len(set2) - k2
-				break
+				pos += len2 - k2
+				return int(pos)
+			}
+			if k1 < len1 {
+			  s1 = set1[k1]
 			}
-			s1 = set1[k1]
 		} else if s1 == s2 {
 			buffer[pos] = s1
 			pos++
 			k1++
 			k2++
-			if k1 >= len(set1) {
+			if k1 >= len1 {
 				copy(buffer[pos:], set2[k2:])
-				pos += len(set2) - k2
+				pos += len2 - k2
 				break
 			}
-			if k2 >= len(set2) {
+			if k2 >= len2 {
 				copy(buffer[pos:], set1[k1:])
-				pos += len(set1) - k1
+				pos += len1 - k1
 				break
 			}
 			s1 = set1[k1]
@@ -51,13 +59,13 @@ func union2by2(set1 []uint16, set2 []uint16, buffer []uint16) int {
 			buffer[pos] = s2
 			pos++
 			k2++
-			if k2 >= len(set2) {
+			if k2 >= len2 {
 				copy(buffer[pos:], set1[k1:])
-				pos += len(set1) - k1
+				pos += len1 - k1
 				break
 			}
 			s2 = set2[k2]
 		}
 	}
-	return pos
+	return int(pos)
 }

From 9f95696ce93b44ce22c97ad064481cab5c2e5771 Mon Sep 17 00:00:00 2001
From: Daniel Lemire <lemire@gmail.com>
Date: Fri, 16 Apr 2021 15:31:32 -0400
Subject: [PATCH 2/3] Tuning.

---
 setutil_generic.go | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/setutil_generic.go b/setutil_generic.go
index 3668f800..aa5bc7d0 100644
--- a/setutil_generic.go
+++ b/setutil_generic.go
@@ -21,8 +21,8 @@ func union2by2(set1 []uint16, set2 []uint16, buffer []uint16) int {
 	}
 	s1 := set1[k1]
 	s2 := set2[k2]
-	buffer = buffer[:cap(buffer)]
-	for {
+	buffer = buffer[:len1 + len2]
+	for pos < uint(len(buffer)) {
 		if pos >= uint(len(buffer)) {
 			panic("You provided a buffer with insufficient capacity")
 		}
@@ -35,9 +35,7 @@ func union2by2(set1 []uint16, set2 []uint16, buffer []uint16) int {
 				pos += len2 - k2
 				return int(pos)
 			}
-			if k1 < len1 {
-			  s1 = set1[k1]
-			}
+			s1 = set1[k1]
 		} else if s1 == s2 {
 			buffer[pos] = s1
 			pos++

From 2e7b454e4198e29b23f64589d15a05f911474096 Mon Sep 17 00:00:00 2001
From: Daniel Lemire <lemire@gmail.com>
Date: Fri, 16 Apr 2021 15:40:34 -0400
Subject: [PATCH 3/3] Removing dead code.

---
 setutil_generic.go | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/setutil_generic.go b/setutil_generic.go
index aa5bc7d0..9fcdd0b6 100644
--- a/setutil_generic.go
+++ b/setutil_generic.go
@@ -23,9 +23,6 @@ func union2by2(set1 []uint16, set2 []uint16, buffer []uint16) int {
 	s2 := set2[k2]
 	buffer = buffer[:len1 + len2]
 	for pos < uint(len(buffer)) {
-		if pos >= uint(len(buffer)) {
-			panic("You provided a buffer with insufficient capacity")
-		}
 		if s1 < s2 {
 			buffer[pos] = s1
 			pos++