Make array Validate require strictly increasing values

arraycontainer.go

@@ -1338,7 +1338,7 @@ func (ac *arrayContainer) addOffset(x uint16) (container, container) {
 	return low, high
 }
 
-// validate checks cardinality and sort order of the array container
+// validate checks cardinality and that content is strictly increasing
 func (ac *arrayContainer) validate() error {
 	cardinality := ac.getCardinality()
 
@@ -1353,7 +1353,7 @@ func (ac *arrayContainer) validate() error {
 	previous := ac.content[0]
 	for i := 1; i < len(ac.content); i++ {
 		next := ac.content[i]
-		if previous > next {
+		if previous >= next {
 			return ErrArrayIncorrectSort
 		}
 		previous = next

arraycontainer_test.go

@@ -628,11 +628,20 @@ func TestArrayContainerValidation(t *testing.T) {
 	array.content[500] = uint16(upperBound + upperBound)
 
 	err = array.validate()
-	assert.Error(t, err)
+	assert.ErrorIs(t, err, ErrArrayIncorrectSort)
 
+	// Adjacent duplicates must be rejected (strictly increasing), matching
+	// CRoaring, Java, and Rust validators (previous >= next).
 	array = newArrayContainer()
+	for i := 0; i < 10; i++ {
+		array.iadd(uint16(i))
+	}
+	array.content[5] = array.content[4]
+	err = array.validate()
+	assert.ErrorIs(t, err, ErrArrayIncorrectSort)
 
-	// Technically a run, but make sure the incorrect sort detection handles equal elements
+	// Repeated iadd of the same value is a no-op; container stays valid.
+	array = newArrayContainer()
 	for i := 0; i < upperBound; i++ {
 		array.iadd(uint16(1))
 	}

roaring_test.go

@@ -3427,6 +3427,24 @@ func TestBitMapValidationFromDeserialization(t *testing.T) {
 			},
 			err: ErrArrayIncorrectSort,
 		},
+		{
+			name: "Array Adjacent Duplicates",
+			loader: func(bm *Bitmap) {
+				arrayEntries := make([]uint32, 0, 10)
+				for i := 0; i < 10; i++ {
+					arrayEntries = append(arrayEntries, uint32(i))
+				}
+				bm.AddMany(arrayEntries)
+			},
+			corruptor: func(s []byte) {
+				// Portable single-container array layout: values start at offset 16
+				// as little-endian uint16s: content[i] at 16+2*i.
+				// Set content[5] equal to content[4] (adjacent duplicate).
+				s[26] = 4
+				s[27] = 0
+			},
+			err: ErrArrayIncorrectSort,
+		},
 	}
 
 	for _, tt := range deserializationTests {