Optimize test for pointer being in a partition on 32-bit.

Source/wtf/PageAllocator.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef WTF_PageAllocator_h
 #define WTF_PageAllocator_h
 
+#include "wtf/Assertions.h"
+#include "wtf/CPU.h"
+#include <stdint.h>
+
 namespace WTF {
 
 // Our granulatity of page allocation is 64KB. This is a Windows limitation,
 // but we apply the same requirement for all platforms in order to keep
 // things simple and consistent.
 // We term these 64KB allocations "super pages". They're just a clump of
 // underlying 4KB system pages.
-static const size_t kSuperPageSize = 1 << 16; // 64KB
+static const size_t kSuperPageShift = 16; // 64KB
+static const size_t kSuperPageSize = 1 << kSuperPageShift;
 static const size_t kSuperPageOffsetMask = kSuperPageSize - 1;
 static const size_t kSuperPageBaseMask = ~kSuperPageOffsetMask;
 
 // All Blink-supported systems have 4096 sized system pages and can handle
 // permissions and commit / decommit at this granularity.
 static const size_t kSystemPageSize = 4096;
 static const size_t kSystemPageOffsetMask = kSystemPageSize - 1;
 
 static const size_t kNumSystemPagesPerSuperPage = kSuperPageSize / kSystemPageSize;
 
@@ skipping 13 matching lines @@
 // Subsequently accessing any address in the range will fault, the addresses
 // will not be re-used by future allocations.
 // len must be a multiple of kSystemPageSize bytes.
 void setSystemPagesInaccessible(void* addr, size_t len);
 
 // Decommit one or more system pages. Decommitted means that the physical memory
 // is released to the system, but the virtual address space remains reserved.
 // System pages are re-committed by writing to them.
 // Clients should not make any assumptions about the contents of decommitted
 // system pages, before or after they write to the page. The only guarantee
-// provided is that the contents of the system page will be deterministic again // after writing to it. In particlar note that system pages are not guaranteed
+// provided is that the contents of the system page will be deterministic again
+// after writing to it. In particlar note that system pages are not guaranteed
 // to be zero-filled upon re-commit.
 // len must be a multiple of kSystemPageSize bytes.
 void decommitSystemPages(void* addr, size_t len);
 
 // Returns a suitable pointer for starting to allocate super pages.
 // The pointer is not guaranteed to be "unused", but does represent an address
 // that has a good chance of being unused. The pointer is also randomized to
 // provide reasonable ASLR.
 char* getRandomSuperPageBase();
 
+class SuperPageBitmap {
+public:
+    ALWAYS_INLINE static bool isAvailable()
+    {
+#if CPU(32BIT)
+        return true;
+#else
+        return false;
+#endif
+    }
+
+    ALWAYS_INLINE static bool isPointerInSuperPage(void* ptr)
+    {
+#if CPU(32BIT)
+        uintptr_t raw = reinterpret_cast<uintptr_t>(ptr);
+        raw >>= kSuperPageShift;
+        size_t idx = raw >> 3;
+        size_t bit = raw & 7;
+        ASSERT(idx < sizeof(s_bitmap));
+        return s_bitmap[idx] & (1 << bit);
+#else
+        ASSERT(false);
+        return false;
+#endif
+    }
+
+    static void registerSuperPage(void* ptr);
+    static void unregisterSuperPage(void* ptr);
+
+private:
+    static unsigned char s_bitmap[1 << (32 - kSuperPageShift - 3)];
+};
+
 } // namespace WTF
 
 #endif // WTF_PageAllocator_h