BitArray.setRange and BitArray.clearRange

Author: isoos

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - Updated SDK constraint, lints and format.
 - `BitArray.setWhere` and `BitArray.clearWhere` for callback-driven updates.
+- `BitArray.setRange` and `BitArray.clearRange` for efficient continous-range updates.
 - More efficient `BitArray` operations: `setAll`, `clearAll`.
 - More efficient `BitArray` operations: `and`, `andNot`, `or`, `xor` when the parameter is another `BitArray`.
 

lib/src/bit_array.dart

@@ -143,6 +143,35 @@ class BitArray extends BitSet {
     }
   }
 
+  /// Sets the bits from [start] (inclusive) up to [end] (exclusive) to false.
+  void clearRange(int start, int end) {
+    assert(start >= 0 && start < _length);
+    assert(start <= end && end <= _length);
+    if (start == end) return;
+    final dataStart = start >> 5;
+    final dataEnd = (end - 1) >> 5;
+    final maskStart = start & 0x1f;
+    final maskEnd = (end - 1) & 0x1f;
+
+    if (dataStart == dataEnd) {
+      for (var i = maskStart; i <= maskEnd; i++) {
+        _data[dataStart] &= _clearMask[i];
+      }
+      return;
+    }
+    if (maskStart == 0) {
+      _data[dataStart] = 0;
+    } else {
+      for (var i = maskStart; i < _clearMask.length; i++) {
+        _data[dataStart] &= _clearMask[i];
+      }
+    }
+    _data.fillRange(dataStart + 1, dataEnd, 0);
+    for (var i = 0; i <= maskEnd; i++) {
+      _data[dataEnd] &= _clearMask[i];
+    }
+  }
+
   /// Sets all of the bits in the current [BitArray] to false.
   void clearAll() {
     _data.fillRange(0, _data.length, 0);
@@ -180,6 +209,35 @@ class BitArray extends BitSet {
     }
   }
 
+  /// Sets the bits from [start] (inclusive) up to [end] (exclusive) to false.
+  void setRange(int start, int end) {
+    assert(start >= 0 && start < _length);
+    assert(start <= end && end <= _length);
+    if (start == end) return;
+    final dataStart = start >> 5;
+    final dataEnd = (end - 1) >> 5;
+    final maskStart = start & 0x1f;
+    final maskEnd = (end - 1) & 0x1f;
+
+    if (dataStart == dataEnd) {
+      for (var i = maskStart; i <= maskEnd; i++) {
+        _data[dataStart] |= _bitMask[i];
+      }
+      return;
+    }
+    if (maskStart == 0) {
+      _data[dataStart] = -1;
+    } else {
+      for (var i = maskStart; i < _bitMask.length; i++) {
+        _data[dataStart] |= _bitMask[i];
+      }
+    }
+    _data.fillRange(dataStart + 1, dataEnd, -1);
+    for (var i = 0; i <= maskEnd; i++) {
+      _data[dataEnd] |= _bitMask[i];
+    }
+  }
+
   /// Sets all the bit values in the current [BitArray] to true.
   void setAll() {
     _data.fillRange(0, _data.length, -1);

test/bit_array_test.dart

@@ -188,6 +188,45 @@ void main() {
         }
       }
     });
+
+    test('clearRange', () {
+      for (var start = 0; start < 128; start++) {
+        for (var end = start; end <= 128; end++) {
+          final array = BitArray(128);
+          array.clearRange(start, end);
+          expect(array.cardinality, 0);
+          array.setAll();
+          array.clearRange(start, end);
+          for (var i = 0; i < 128; i++) {
+            expect(
+              array[i],
+              i < start || i >= end,
+              reason: '$start-$end $i ${array[i]}',
+            );
+          }
+        }
+      }
+    });
+
+    test('setRange', () {
+      for (var start = 0; start < 128; start++) {
+        for (var end = start; end <= 128; end++) {
+          final array = BitArray(128);
+          array.setAll();
+          array.setRange(start, end);
+          expect(array.cardinality, 128);
+          array.clearAll();
+          array.setRange(start, end);
+          for (var i = 0; i < 128; i++) {
+            expect(
+              array[i],
+              i >= start && i < end,
+              reason: '$start-$end $i ${array[i]}',
+            );
+          }
+        }
+      }
+    });
   });
 
   group('BitArray equals and hashCode', () {