First step towards implementing stack map descriptions for the optimizing compiler.

vm/bitmap.h

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef VM_BITMAP_H_
+#define VM_BITMAP_H_
+
+#include "vm/allocation.h"
+
+namespace dart {
+
+// Forward declarations.
+class Bitmap;
+class RawBitmap;
+
+
+// BitmapBuilder is used to build a bitmap. The implementation is optimized for
+// a dense set of small bit maps without an upper bound (e.g: a pointer map
+// description of a stack).
+class BitmapBuilder : public ZoneAllocated {
+ public:
+  BitmapBuilder() : size_(kInitialSize), bit_list_dynamic_(NULL) {
+    memset(bit_list_, 0, kInitialSize);
+  }
+
+  // Get/Set individual bits in the bitmap, set expands the underlying bitmap
+  // if needed.
+  bool Get(int32_t bit_offset) const;
+  void Set(int32_t bit_offset, bool value);
+
+  // Return the bit offset of the highest bit set.
+  int32_t Maximum() const;

[srdjan, 2012/03/14 17:31:32]

intptr_t instead of int32_t for the offsets? Here and elsewhere.

[siva, 2012/03/14 22:54:20]

Done.

+
+  // Return the bit offset of the lowest bit set.
+  int32_t Minimum() const;
+
+  // Sets min..max (inclusive) to value.
+  void SetRange(int32_t min, int32_t max, bool value);
+
+  // Replicates the bit map setting of the passed in Bitmap object.
+  void SetBits(const Bitmap& bitmap);
+
+  // Returns a Bitmap object corrsponding to the bits built up so far.
+  RawBitmap* GetBitmap() const;
+
+ private:
+  static const int32_t kInitialSize = 16;
+  static const int32_t kIncrementSize = 16;
+
+  int32_t BitSize() const { return (size_ * kBitsPerByte); }

[srdjan, 2012/03/14 17:31:32]

Is it more readable to say SizeInBits?

[siva, 2012/03/14 22:54:20]

Done.

+
+  bool InRange(int32_t offset) const {
+    return (offset >= 0) && (offset < BitSize());
+  }
+
+  bool GetBit(int32_t bit_offset) const;
+  void SetBit(int32_t bit_offset, bool value);
+
+  int32_t size_;
+  uint8_t bit_list_[kInitialSize];

[srdjan, 2012/03/14 17:31:32]

Should this then be kInitialSizeInBytes? Size it typical word size, I think.

[siva, 2012/03/14 22:54:20]

Done.

+  uint8_t* bit_list_dynamic_;
+
+  DISALLOW_COPY_AND_ASSIGN(BitmapBuilder);
+};
+
+}  // namespace dart
+
+#endif  // VM_BITMAP_H_