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      1 //===- llvm/ADT/SmallBitVector.h - 'Normally small' bit vectors -*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file implements the SmallBitVector class.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #ifndef LLVM_ADT_SMALLBITVECTOR_H
     15 #define LLVM_ADT_SMALLBITVECTOR_H
     16 
     17 #include "llvm/ADT/BitVector.h"
     18 #include "llvm/Support/MathExtras.h"
     19 #include <cassert>
     20 
     21 namespace llvm {
     22 
     23 /// SmallBitVector - This is a 'bitvector' (really, a variable-sized bit array),
     24 /// optimized for the case when the array is small.  It contains one
     25 /// pointer-sized field, which is directly used as a plain collection of bits
     26 /// when possible, or as a pointer to a larger heap-allocated array when
     27 /// necessary.  This allows normal "small" cases to be fast without losing
     28 /// generality for large inputs.
     29 ///
     30 class SmallBitVector {
     31   // TODO: In "large" mode, a pointer to a BitVector is used, leading to an
     32   // unnecessary level of indirection. It would be more efficient to use a
     33   // pointer to memory containing size, allocation size, and the array of bits.
     34   uintptr_t X;
     35 
     36   enum {
     37     // The number of bits in this class.
     38     NumBaseBits = sizeof(uintptr_t) * CHAR_BIT,
     39 
     40     // One bit is used to discriminate between small and large mode. The
     41     // remaining bits are used for the small-mode representation.
     42     SmallNumRawBits = NumBaseBits - 1,
     43 
     44     // A few more bits are used to store the size of the bit set in small mode.
     45     // Theoretically this is a ceil-log2. These bits are encoded in the most
     46     // significant bits of the raw bits.
     47     SmallNumSizeBits = (NumBaseBits == 32 ? 5 :
     48                         NumBaseBits == 64 ? 6 :
     49                         SmallNumRawBits),
     50 
     51     // The remaining bits are used to store the actual set in small mode.
     52     SmallNumDataBits = SmallNumRawBits - SmallNumSizeBits
     53   };
     54 
     55 public:
     56   // Encapsulation of a single bit.
     57   class reference {
     58     SmallBitVector &TheVector;
     59     unsigned BitPos;
     60 
     61   public:
     62     reference(SmallBitVector &b, unsigned Idx) : TheVector(b), BitPos(Idx) {}
     63 
     64     reference& operator=(reference t) {
     65       *this = bool(t);
     66       return *this;
     67     }
     68 
     69     reference& operator=(bool t) {
     70       if (t)
     71         TheVector.set(BitPos);
     72       else
     73         TheVector.reset(BitPos);
     74       return *this;
     75     }
     76 
     77     operator bool() const {
     78       return const_cast<const SmallBitVector &>(TheVector).operator[](BitPos);
     79     }
     80   };
     81 
     82 private:
     83   bool isSmall() const {
     84     return X & uintptr_t(1);
     85   }
     86 
     87   BitVector *getPointer() const {
     88     assert(!isSmall());
     89     return reinterpret_cast<BitVector *>(X);
     90   }
     91 
     92   void switchToSmall(uintptr_t NewSmallBits, size_t NewSize) {
     93     X = 1;
     94     setSmallSize(NewSize);
     95     setSmallBits(NewSmallBits);
     96   }
     97 
     98   void switchToLarge(BitVector *BV) {
     99     X = reinterpret_cast<uintptr_t>(BV);
    100     assert(!isSmall() && "Tried to use an unaligned pointer");
    101   }
    102 
    103   // Return all the bits used for the "small" representation; this includes
    104   // bits for the size as well as the element bits.
    105   uintptr_t getSmallRawBits() const {
    106     assert(isSmall());
    107     return X >> 1;
    108   }
    109 
    110   void setSmallRawBits(uintptr_t NewRawBits) {
    111     assert(isSmall());
    112     X = (NewRawBits << 1) | uintptr_t(1);
    113   }
    114 
    115   // Return the size.
    116   size_t getSmallSize() const {
    117     return getSmallRawBits() >> SmallNumDataBits;
    118   }
    119 
    120   void setSmallSize(size_t Size) {
    121     setSmallRawBits(getSmallBits() | (Size << SmallNumDataBits));
    122   }
    123 
    124   // Return the element bits.
    125   uintptr_t getSmallBits() const {
    126     return getSmallRawBits() & ~(~uintptr_t(0) << getSmallSize());
    127   }
    128 
    129   void setSmallBits(uintptr_t NewBits) {
    130     setSmallRawBits((NewBits & ~(~uintptr_t(0) << getSmallSize())) |
    131                     (getSmallSize() << SmallNumDataBits));
    132   }
    133 
    134 public:
    135   /// SmallBitVector default ctor - Creates an empty bitvector.
    136   SmallBitVector() : X(1) {}
    137 
    138   /// SmallBitVector ctor - Creates a bitvector of specified number of bits. All
    139   /// bits are initialized to the specified value.
    140   explicit SmallBitVector(unsigned s, bool t = false) {
    141     if (s <= SmallNumDataBits)
    142       switchToSmall(t ? ~uintptr_t(0) : 0, s);
    143     else
    144       switchToLarge(new BitVector(s, t));
    145   }
    146 
    147   /// SmallBitVector copy ctor.
    148   SmallBitVector(const SmallBitVector &RHS) {
    149     if (RHS.isSmall())
    150       X = RHS.X;
    151     else
    152       switchToLarge(new BitVector(*RHS.getPointer()));
    153   }
    154 
    155   ~SmallBitVector() {
    156     if (!isSmall())
    157       delete getPointer();
    158   }
    159 
    160   /// empty - Tests whether there are no bits in this bitvector.
    161   bool empty() const {
    162     return isSmall() ? getSmallSize() == 0 : getPointer()->empty();
    163   }
    164 
    165   /// size - Returns the number of bits in this bitvector.
    166   size_t size() const {
    167     return isSmall() ? getSmallSize() : getPointer()->size();
    168   }
    169 
    170   /// count - Returns the number of bits which are set.
    171   unsigned count() const {
    172     if (isSmall()) {
    173       uintptr_t Bits = getSmallBits();
    174       if (sizeof(uintptr_t) * CHAR_BIT == 32)
    175         return CountPopulation_32(Bits);
    176       if (sizeof(uintptr_t) * CHAR_BIT == 64)
    177         return CountPopulation_64(Bits);
    178       assert(0 && "Unsupported!");
    179     }
    180     return getPointer()->count();
    181   }
    182 
    183   /// any - Returns true if any bit is set.
    184   bool any() const {
    185     if (isSmall())
    186       return getSmallBits() != 0;
    187     return getPointer()->any();
    188   }
    189 
    190   /// all - Returns true if all bits are set.
    191   bool all() const {
    192     if (isSmall())
    193       return getSmallBits() == (uintptr_t(1) << getSmallSize()) - 1;
    194     return getPointer()->all();
    195   }
    196 
    197   /// none - Returns true if none of the bits are set.
    198   bool none() const {
    199     if (isSmall())
    200       return getSmallBits() == 0;
    201     return getPointer()->none();
    202   }
    203 
    204   /// find_first - Returns the index of the first set bit, -1 if none
    205   /// of the bits are set.
    206   int find_first() const {
    207     if (isSmall()) {
    208       uintptr_t Bits = getSmallBits();
    209       if (Bits == 0)
    210         return -1;
    211       if (sizeof(uintptr_t) * CHAR_BIT == 32)
    212         return CountTrailingZeros_32(Bits);
    213       if (sizeof(uintptr_t) * CHAR_BIT == 64)
    214         return CountTrailingZeros_64(Bits);
    215       assert(0 && "Unsupported!");
    216     }
    217     return getPointer()->find_first();
    218   }
    219 
    220   /// find_next - Returns the index of the next set bit following the
    221   /// "Prev" bit. Returns -1 if the next set bit is not found.
    222   int find_next(unsigned Prev) const {
    223     if (isSmall()) {
    224       uintptr_t Bits = getSmallBits();
    225       // Mask off previous bits.
    226       Bits &= ~uintptr_t(0) << (Prev + 1);
    227       if (Bits == 0 || Prev + 1 >= getSmallSize())
    228         return -1;
    229       if (sizeof(uintptr_t) * CHAR_BIT == 32)
    230         return CountTrailingZeros_32(Bits);
    231       if (sizeof(uintptr_t) * CHAR_BIT == 64)
    232         return CountTrailingZeros_64(Bits);
    233       assert(0 && "Unsupported!");
    234     }
    235     return getPointer()->find_next(Prev);
    236   }
    237 
    238   /// clear - Clear all bits.
    239   void clear() {
    240     if (!isSmall())
    241       delete getPointer();
    242     switchToSmall(0, 0);
    243   }
    244 
    245   /// resize - Grow or shrink the bitvector.
    246   void resize(unsigned N, bool t = false) {
    247     if (!isSmall()) {
    248       getPointer()->resize(N, t);
    249     } else if (SmallNumDataBits >= N) {
    250       uintptr_t NewBits = t ? ~uintptr_t(0) << getSmallSize() : 0;
    251       setSmallSize(N);
    252       setSmallBits(NewBits | getSmallBits());
    253     } else {
    254       BitVector *BV = new BitVector(N, t);
    255       uintptr_t OldBits = getSmallBits();
    256       for (size_t i = 0, e = getSmallSize(); i != e; ++i)
    257         (*BV)[i] = (OldBits >> i) & 1;
    258       switchToLarge(BV);
    259     }
    260   }
    261 
    262   void reserve(unsigned N) {
    263     if (isSmall()) {
    264       if (N > SmallNumDataBits) {
    265         uintptr_t OldBits = getSmallRawBits();
    266         size_t SmallSize = getSmallSize();
    267         BitVector *BV = new BitVector(SmallSize);
    268         for (size_t i = 0; i < SmallSize; ++i)
    269           if ((OldBits >> i) & 1)
    270             BV->set(i);
    271         BV->reserve(N);
    272         switchToLarge(BV);
    273       }
    274     } else {
    275       getPointer()->reserve(N);
    276     }
    277   }
    278 
    279   // Set, reset, flip
    280   SmallBitVector &set() {
    281     if (isSmall())
    282       setSmallBits(~uintptr_t(0));
    283     else
    284       getPointer()->set();
    285     return *this;
    286   }
    287 
    288   SmallBitVector &set(unsigned Idx) {
    289     if (isSmall())
    290       setSmallBits(getSmallBits() | (uintptr_t(1) << Idx));
    291     else
    292       getPointer()->set(Idx);
    293     return *this;
    294   }
    295 
    296   SmallBitVector &reset() {
    297     if (isSmall())
    298       setSmallBits(0);
    299     else
    300       getPointer()->reset();
    301     return *this;
    302   }
    303 
    304   SmallBitVector &reset(unsigned Idx) {
    305     if (isSmall())
    306       setSmallBits(getSmallBits() & ~(uintptr_t(1) << Idx));
    307     else
    308       getPointer()->reset(Idx);
    309     return *this;
    310   }
    311 
    312   SmallBitVector &flip() {
    313     if (isSmall())
    314       setSmallBits(~getSmallBits());
    315     else
    316       getPointer()->flip();
    317     return *this;
    318   }
    319 
    320   SmallBitVector &flip(unsigned Idx) {
    321     if (isSmall())
    322       setSmallBits(getSmallBits() ^ (uintptr_t(1) << Idx));
    323     else
    324       getPointer()->flip(Idx);
    325     return *this;
    326   }
    327 
    328   // No argument flip.
    329   SmallBitVector operator~() const {
    330     return SmallBitVector(*this).flip();
    331   }
    332 
    333   // Indexing.
    334   reference operator[](unsigned Idx) {
    335     assert(Idx < size() && "Out-of-bounds Bit access.");
    336     return reference(*this, Idx);
    337   }
    338 
    339   bool operator[](unsigned Idx) const {
    340     assert(Idx < size() && "Out-of-bounds Bit access.");
    341     if (isSmall())
    342       return ((getSmallBits() >> Idx) & 1) != 0;
    343     return getPointer()->operator[](Idx);
    344   }
    345 
    346   bool test(unsigned Idx) const {
    347     return (*this)[Idx];
    348   }
    349 
    350   // Comparison operators.
    351   bool operator==(const SmallBitVector &RHS) const {
    352     if (size() != RHS.size())
    353       return false;
    354     if (isSmall())
    355       return getSmallBits() == RHS.getSmallBits();
    356     else
    357       return *getPointer() == *RHS.getPointer();
    358   }
    359 
    360   bool operator!=(const SmallBitVector &RHS) const {
    361     return !(*this == RHS);
    362   }
    363 
    364   // Intersection, union, disjoint union.
    365   SmallBitVector &operator&=(const SmallBitVector &RHS) {
    366     resize(std::max(size(), RHS.size()));
    367     if (isSmall())
    368       setSmallBits(getSmallBits() & RHS.getSmallBits());
    369     else if (!RHS.isSmall())
    370       getPointer()->operator&=(*RHS.getPointer());
    371     else {
    372       SmallBitVector Copy = RHS;
    373       Copy.resize(size());
    374       getPointer()->operator&=(*Copy.getPointer());
    375     }
    376     return *this;
    377   }
    378 
    379   SmallBitVector &operator|=(const SmallBitVector &RHS) {
    380     resize(std::max(size(), RHS.size()));
    381     if (isSmall())
    382       setSmallBits(getSmallBits() | RHS.getSmallBits());
    383     else if (!RHS.isSmall())
    384       getPointer()->operator|=(*RHS.getPointer());
    385     else {
    386       SmallBitVector Copy = RHS;
    387       Copy.resize(size());
    388       getPointer()->operator|=(*Copy.getPointer());
    389     }
    390     return *this;
    391   }
    392 
    393   SmallBitVector &operator^=(const SmallBitVector &RHS) {
    394     resize(std::max(size(), RHS.size()));
    395     if (isSmall())
    396       setSmallBits(getSmallBits() ^ RHS.getSmallBits());
    397     else if (!RHS.isSmall())
    398       getPointer()->operator^=(*RHS.getPointer());
    399     else {
    400       SmallBitVector Copy = RHS;
    401       Copy.resize(size());
    402       getPointer()->operator^=(*Copy.getPointer());
    403     }
    404     return *this;
    405   }
    406 
    407   // Assignment operator.
    408   const SmallBitVector &operator=(const SmallBitVector &RHS) {
    409     if (isSmall()) {
    410       if (RHS.isSmall())
    411         X = RHS.X;
    412       else
    413         switchToLarge(new BitVector(*RHS.getPointer()));
    414     } else {
    415       if (!RHS.isSmall())
    416         *getPointer() = *RHS.getPointer();
    417       else {
    418         delete getPointer();
    419         X = RHS.X;
    420       }
    421     }
    422     return *this;
    423   }
    424 
    425   void swap(SmallBitVector &RHS) {
    426     std::swap(X, RHS.X);
    427   }
    428 };
    429 
    430 inline SmallBitVector
    431 operator&(const SmallBitVector &LHS, const SmallBitVector &RHS) {
    432   SmallBitVector Result(LHS);
    433   Result &= RHS;
    434   return Result;
    435 }
    436 
    437 inline SmallBitVector
    438 operator|(const SmallBitVector &LHS, const SmallBitVector &RHS) {
    439   SmallBitVector Result(LHS);
    440   Result |= RHS;
    441   return Result;
    442 }
    443 
    444 inline SmallBitVector
    445 operator^(const SmallBitVector &LHS, const SmallBitVector &RHS) {
    446   SmallBitVector Result(LHS);
    447   Result ^= RHS;
    448   return Result;
    449 }
    450 
    451 } // End llvm namespace
    452 
    453 namespace std {
    454   /// Implement std::swap in terms of BitVector swap.
    455   inline void
    456   swap(llvm::SmallBitVector &LHS, llvm::SmallBitVector &RHS) {
    457     LHS.swap(RHS);
    458   }
    459 }
    460 
    461 #endif
    462