1 files changed, 82 insertions, 0 deletions
diff --git a/js/src/ds/BitArray.h b/js/src/ds/BitArray.h
new file mode 100644
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+++ b/js/src/ds/BitArray.h
@@ -0,0 +1,82 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef ds_BitArray_h
+#define ds_BitArray_h
+
+#include "mozilla/TemplateLib.h"
+
+#include <limits.h>
+
+#include "jstypes.h"
+
+namespace js {
+
+template <size_t nbits>
+class BitArray
+{
+  private:
+    // Use a 32 bit word to make it easier to access a BitArray from JIT code.
+    using WordT = uint32_t;
+
+    static const size_t bitsPerElement = sizeof(WordT) * CHAR_BIT;
+    static const size_t numSlots = nbits / bitsPerElement + (nbits % bitsPerElement == 0 ? 0 : 1);
+    static const size_t paddingBits = (numSlots * bitsPerElement) - nbits;
+    static_assert(paddingBits < bitsPerElement, "More padding bits than expected.");
+    static const WordT paddingMask = WordT(-1) >> paddingBits;
+
+    WordT map[numSlots];
+
+  public:
+    void clear(bool value) {
+        memset(map, value ? 0xFF : 0, sizeof(map));
+        if (value)
+            map[numSlots - 1] &= paddingMask;
+    }
+
+    inline bool get(size_t offset) const {
+        size_t index;
+        WordT mask;
+        getIndexAndMask(offset, &index, &mask);
+        return map[index] & mask;
+    }
+
+    void set(size_t offset) {
+        size_t index;
+        WordT mask;
+        getIndexAndMask(offset, &index, &mask);
+        map[index] |= mask;
+    }
+
+    void unset(size_t offset) {
+        size_t index;
+        WordT mask;
+        getIndexAndMask(offset, &index, &mask);
+        map[index] &= ~mask;
+    }
+
+    bool isAllClear() const {
+        for (size_t i = 0; i < numSlots; i++) {
+            if (map[i])
+                return false;
+        }
+        return true;
+    }
+
+    static void getIndexAndMask(size_t offset, size_t* indexp, WordT* maskp) {
+        static_assert(bitsPerElement == 32, "unexpected bitsPerElement value");
+        *indexp = offset / bitsPerElement;
+        *maskp = WordT(1) << (offset % bitsPerElement);
+    }
+
+    static size_t offsetOfMap() {
+        return offsetof(BitArray<nbits>, map);
+    }
+};
+
+} /* namespace js */
+
+#endif /* ds_BitArray_h */