From c6ff00561d0ed27d0a0e092c713812a3279272b1 Mon Sep 17 00:00:00 2001
From: Daniel Lemire <daniel@lemire.me>
Date: Tue, 24 Jan 2023 10:43:58 -0500
Subject: [PATCH 1/2] Fixing issue 116.

---
 bitset.go | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/bitset.go b/bitset.go
index fbf0496..d0fbff9 100644
--- a/bitset.go
+++ b/bitset.go
@@ -115,6 +115,12 @@ func wordsNeeded(i uint) int {
 	return int((i + (wordSize - 1)) >> log2WordSize)
 }
 
+// wordsNeededUnbound calculates the number of words needed for i bits, possibly exceeding the capacity.
+// This function is useful if you know that the capacity cannot be exceeded (e.g., you have an existing bitmap).
+func wordsNeededUnbound(i uint) int {
+	return int((i + (wordSize - 1)) >> log2WordSize)
+}
+
 // wordsIndex calculates the index of words in a `uint64`
 func wordsIndex(i uint) uint {
 	return i & (wordSize - 1)
@@ -530,7 +536,7 @@ func (b *BitSet) ClearAll() *BitSet {
 
 // wordCount returns the number of words used in a bit set
 func (b *BitSet) wordCount() int {
-	return len(b.set)
+	return wordsNeededUnbound(b.length)
 }
 
 // Clone this BitSet
@@ -606,10 +612,9 @@ func (b *BitSet) Equal(c *BitSet) bool {
 	if b.length == 0 { // if they have both length == 0, then could have nil set
 		return true
 	}
-	// testing for equality shoud not transform the bitset (no call to safeSet)
-
-	for p, v := range b.set {
-		if c.set[p] != v {
+	wn := b.wordCount()
+	for p:= 0; p < wn; p++ {
+		if c.set[p] != b.set[p] {
 			return false
 		}
 	}
@@ -898,7 +903,7 @@ func (b *BitSet) DumpAsBits() string {
 
 // BinaryStorageSize returns the binary storage requirements
 func (b *BitSet) BinaryStorageSize() int {
-	nWords := wordsNeeded(b.length)
+	nWords := b.wordCount()
 	return binary.Size(uint64(0)) + binary.Size(b.set[:nWords])
 }
 
@@ -917,7 +922,7 @@ func (b *BitSet) WriteTo(stream io.Writer) (int64, error) {
 	// binary.Write for large set
 	writer := bufio.NewWriter(stream)
 	var item = make([]byte, binary.Size(uint64(0))) // for serializing one uint64
-	nWords := wordsNeeded(uint(length))
+	nWords := b.wordCount()
 	for i := range b.set[:nWords] {
 		binaryOrder.PutUint64(item, b.set[i])
 		if nn, err := writer.Write(item); err != nil {
@@ -948,7 +953,7 @@ func (b *BitSet) ReadFrom(stream io.Reader) (int64, error) {
 	}
 
 	var item [8]byte
-	nWords := wordsNeeded(uint(length))
+	nWords := wordsNeeded(uint(length))//b.wordCount()
 	reader := bufio.NewReader(io.LimitReader(stream, 8*int64(nWords)))
 	for i := 0; i < nWords; i++ {
 		if _, err := io.ReadFull(reader, item[:]); err != nil {

From 184222871a2a579150c6f7a797e2c948514461d5 Mon Sep 17 00:00:00 2001
From: Daniel Lemire <daniel@lemire.me>
Date: Tue, 24 Jan 2023 10:49:18 -0500
Subject: [PATCH 2/2] Verifying.

---
 bitset.go      |  2 +-
 bitset_test.go | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/bitset.go b/bitset.go
index d0fbff9..5751b68 100644
--- a/bitset.go
+++ b/bitset.go
@@ -953,7 +953,7 @@ func (b *BitSet) ReadFrom(stream io.Reader) (int64, error) {
 	}
 
 	var item [8]byte
-	nWords := wordsNeeded(uint(length))//b.wordCount()
+	nWords := wordsNeeded(uint(length))
 	reader := bufio.NewReader(io.LimitReader(stream, 8*int64(nWords)))
 	for i := 0; i < nWords; i++ {
 		if _, err := io.ReadFull(reader, item[:]); err != nil {
diff --git a/bitset_test.go b/bitset_test.go
index efa202f..601c274 100644
--- a/bitset_test.go
+++ b/bitset_test.go
@@ -1395,6 +1395,16 @@ func TestSetBitsetFrom(t *testing.T) {
 	}
 }
 
+func TestIssue116(t *testing.T) {
+	a := []uint64{2, 3, 5, 7, 11}
+	b := []uint64{2, 3, 5, 7, 11, 0, 1}
+	bitset1 := FromWithLength(320, a)
+	bitset2 := FromWithLength(320, b)
+	if !bitset1.Equal(bitset2) || !bitset2.Equal(bitset1) {
+		t.Error("Bitsets should be equal irrespective of the underlying capacity")
+	}
+}
+
 func TestFrom(t *testing.T) {
 	u := []uint64{2, 3, 5, 7, 11}
 	b := From(u)