1 files changed, 114 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 +1,114 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * 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/MathAlgorithms.h"
+#include "mozilla/TemplateLib.h"
+
+#include <limits.h>
+#include <string.h>
+
+#include "jstypes.h"
+
+namespace js {
+
+namespace detail {
+
+template <typename WordT>
+inline uint_fast8_t CountTrailingZeroes(WordT word);
+
+template <>
+inline uint_fast8_t CountTrailingZeroes(uint32_t word) {
+  return mozilla::CountTrailingZeroes32(word);
+}
+
+template <>
+inline uint_fast8_t CountTrailingZeroes(uint64_t word) {
+  return mozilla::CountTrailingZeroes64(word);
+}
+
+}  // namespace detail
+
+template <size_t nbits>
+class BitArray {
+ public:
+  // 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);
+
+ private:
+  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:
+  constexpr BitArray() : map(){};
+
+  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);
+    MOZ_ASSERT(index < nbits);
+    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;
+  }
+
+  // For iterating over the set bits in the bit array, get a word at a time.
+  WordT getWord(size_t elementIndex) const {
+    MOZ_ASSERT(elementIndex < nbits);
+    return map[elementIndex];
+  }
+
+  static void getIndexAndMask(size_t offset, size_t* indexp, WordT* maskp) {
+    MOZ_ASSERT(offset < nbits);
+    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 */