Add isPositive for symmetry with isNegative.

[oota-llvm.git] / include / llvm / ADT / SmallPtrSet.h

diff --git a/include/llvm/ADT/SmallPtrSet.h b/include/llvm/ADT/SmallPtrSet.h
index a1ce7ba0dc5d364aa44c751a02c77687fedf80d5..f77eb7d8ca71009b8d68e7e6b955c282726ceae9 100644 (file)
--- a/include/llvm/ADT/SmallPtrSet.h
+++ b/include/llvm/ADT/SmallPtrSet.h
@@ -7,7 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This file defines the SmallPtrSet class.
+// This file defines the SmallPtrSet class.  See the doxygen comment for
+// SmallPtrSetImpl for more details on the algorithm used.
 //
 //===----------------------------------------------------------------------===//
 
@@ -16,9 +17,28 @@
 
 #include <cassert>
 #include <cstring>
+#include "llvm/Support/DataTypes.h"
 
 namespace llvm {
 
+/// SmallPtrSetImpl - This is the common code shared among all the
+/// SmallPtrSet<>'s, which is almost everything.  SmallPtrSet has two modes, one
+/// for small and one for large sets.
+///
+/// Small sets use an array of pointers allocated in the SmallPtrSet object,
+/// which is treated as a simple array of pointers.  When a pointer is added to
+/// the set, the array is scanned to see if the element already exists, if not
+/// the element is 'pushed back' onto the array.  If we run out of space in the
+/// array, we grow into the 'large set' case.  SmallSet should be used when the
+/// sets are often small.  In this case, no memory allocation is used, and only
+/// light-weight and cache-efficient scanning is used.
+///
+/// Large sets use a classic exponentially-probed hash table.  Empty buckets are
+/// represented with an illegal pointer value (-1) to allow null pointers to be
+/// inserted.  Tombstones are represented with another illegal pointer value
+/// (-2), to allow deletion.  The hash table is resized when the table is 3/4 or
+/// more.  When this happens, the table is doubled in size.
+///
 class SmallPtrSetImpl {
 protected:
   /// CurArray - This is the current set of buckets.  If it points to
@@ -31,6 +51,7 @@ protected:
   
   // If small, this is # elts allocated consequtively
   unsigned NumElements;
+  unsigned NumTombstones;
   void *SmallArray[1];  // Must be last ivar.
 public:
   SmallPtrSetImpl(unsigned SmallSize) {
@@ -48,8 +69,9 @@ public:
       delete[] CurArray;
   }
   
-  bool isSmall() const { return CurArray == &SmallArray[0]; }
-
+  bool empty() const { return size() == 0; }
+  unsigned size() const { return NumElements; }
+  
   static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
   static void *getEmptyMarker() {
     // Note that -1 is chosen to make clear() efficiently implementable with
@@ -61,12 +83,17 @@ public:
     // Fill the array with empty markers.
     memset(CurArray, -1, CurArraySize*sizeof(void*));
     NumElements = 0;
+    NumTombstones = 0;
   }
   
   /// insert - This returns true if the pointer was new to the set, false if it
   /// was already in the set.
   bool insert(void *Ptr);
   
+  /// erase - If the set contains the specified pointer, remove it and return
+  /// true, otherwise return false.
+  bool erase(void *Ptr);
+  
   bool count(void *Ptr) const {
     if (isSmall()) {
       // Linear search for the item.
@@ -82,6 +109,8 @@ public:
   }
   
 private:
+  bool isSmall() const { return CurArray == &SmallArray[0]; }
+
   unsigned Hash(void *Ptr) const {
     return ((uintptr_t)Ptr >> 4) & (CurArraySize-1);
   }
@@ -142,13 +171,43 @@ public:
   }
 };
 
+/// NextPowerOfTwo - This is a helper template that rounds N up to the next
+/// power of two.
+template<unsigned N>
+struct NextPowerOfTwo;
+
+/// NextPowerOfTwoH - If N is not a power of two, increase it.  This is a helper
+/// template used to implement NextPowerOfTwo.
+template<unsigned N, bool isPowerTwo>
+struct NextPowerOfTwoH {
+  enum { Val = N };
+};
+template<unsigned N>
+struct NextPowerOfTwoH<N, false> {
+  enum {
+    // We could just use NextVal = N+1, but this converges faster.  N|(N-1) sets
+    // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
+    Val = NextPowerOfTwo<(N|(N-1)) + 1>::Val
+  };
+};
+
+template<unsigned N>
+struct NextPowerOfTwo {
+  enum { Val = NextPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
+};
+
 
-/// SmallPtrSet - This class implements 
+/// SmallPtrSet - This class implements a set which is optimizer for holding
+/// SmallSize or less elements.  This internally rounds up SmallSize to the next
+/// power of two if it is not already a power of two.  See the comments above
+/// SmallPtrSetImpl for details of the algorithm.
 template<class PtrType, unsigned SmallSize>
 class SmallPtrSet : public SmallPtrSetImpl {
-  void *SmallArray[SmallSize];
+  // Make sure that SmallSize is a power of two, round up if not.
+  enum { SmallSizePowTwo = NextPowerOfTwo<SmallSize>::Val };
+  void *SmallArray[SmallSizePowTwo];
 public:
-  SmallPtrSet() : SmallPtrSetImpl(SmallSize) {}
+  SmallPtrSet() : SmallPtrSetImpl(NextPowerOfTwo<SmallSizePowTwo>::Val) {}
   
   typedef SmallPtrSetIterator<PtrType> iterator;
   typedef SmallPtrSetIterator<PtrType> const_iterator;