From a1cbd25ceaff1ab298754d3855009d2d0c6980c5 Mon Sep 17 00:00:00 2001
From: Daniel Lemire <lemire@gmail.com>
Date: Fri, 4 Mar 2022 17:04:56 -0500
Subject: [PATCH] Verifying and checking issue 92.

---
 bitset.go      |  4 +++-
 bitset_test.go | 12 ++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/bitset.go b/bitset.go
index 8eff273..d60eaf2 100644
--- a/bitset.go
+++ b/bitset.go
@@ -226,7 +226,9 @@ func (b *BitSet) FlipRange(start, end uint) *BitSet {
 	for i := startWord; i < endWord; i++ {
 		b.set[i] = ^b.set[i]
 	}
-	b.set[endWord] ^= ^uint64(0) >> (-end & (wordSize - 1))
+	if end & (wordSize - 1) != 0 {
+		b.set[endWord] ^= ^uint64(0) >> (-end & (wordSize - 1))
+    }
 	return b
 }
 
diff --git a/bitset_test.go b/bitset_test.go
index 7df653f..a4abf72 100644
--- a/bitset_test.go
+++ b/bitset_test.go
@@ -1409,6 +1409,18 @@ func TestFlipRange(t *testing.T) {
 		t.Error("Unexpected value: ", d.length)
 		return
 	}
+	//
+	for i := uint(0); i < 256; i++ {
+		for j := uint(0); j <= i; j++ {
+			bits := New(i)
+			bits.FlipRange(0, j)
+			c := bits.Count()
+			if c != j {
+				t.Error("Unexpected value: ", c, " expected: ", j)
+				return
+			}
+		}
+	}
 }
 
 func TestCopy(t *testing.T) {