diff options
Diffstat (limited to 'include/llvm/ADT/BitVector.h')
| -rw-r--r-- | include/llvm/ADT/BitVector.h | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/include/llvm/ADT/BitVector.h b/include/llvm/ADT/BitVector.h index 8240d01ae977..e48c023ae7df 100644 --- a/include/llvm/ADT/BitVector.h +++ b/include/llvm/ADT/BitVector.h @@ -14,6 +14,8 @@ #ifndef LLVM_ADT_BITVECTOR_H #define LLVM_ADT_BITVECTOR_H +#include "llvm/ADT/ArrayRef.h" +#include "llvm/ADT/STLExtras.h" #include "llvm/Support/MathExtras.h" #include <algorithm> #include <cassert> @@ -455,6 +457,105 @@ public: return *this; } + BitVector &operator>>=(unsigned N) { + assert(N <= Size); + if (LLVM_UNLIKELY(empty() || N == 0)) + return *this; + + unsigned NumWords = NumBitWords(Size); + assert(NumWords >= 1); + + wordShr(N / BITWORD_SIZE); + + unsigned BitDistance = N % BITWORD_SIZE; + if (BitDistance == 0) + return *this; + + // When the shift size is not a multiple of the word size, then we have + // a tricky situation where each word in succession needs to extract some + // of the bits from the next word and or them into this word while + // shifting this word to make room for the new bits. This has to be done + // for every word in the array. + + // Since we're shifting each word right, some bits will fall off the end + // of each word to the right, and empty space will be created on the left. + // The final word in the array will lose bits permanently, so starting at + // the beginning, work forwards shifting each word to the right, and + // OR'ing in the bits from the end of the next word to the beginning of + // the current word. + + // Example: + // Starting with {0xAABBCCDD, 0xEEFF0011, 0x22334455} and shifting right + // by 4 bits. + // Step 1: Word[0] >>= 4 ; 0x0ABBCCDD + // Step 2: Word[0] |= 0x10000000 ; 0x1ABBCCDD + // Step 3: Word[1] >>= 4 ; 0x0EEFF001 + // Step 4: Word[1] |= 0x50000000 ; 0x5EEFF001 + // Step 5: Word[2] >>= 4 ; 0x02334455 + // Result: { 0x1ABBCCDD, 0x5EEFF001, 0x02334455 } + const BitWord Mask = maskTrailingOnes<BitWord>(BitDistance); + const unsigned LSH = BITWORD_SIZE - BitDistance; + + for (unsigned I = 0; I < NumWords - 1; ++I) { + Bits[I] >>= BitDistance; + Bits[I] |= (Bits[I + 1] & Mask) << LSH; + } + + Bits[NumWords - 1] >>= BitDistance; + + return *this; + } + + BitVector &operator<<=(unsigned N) { + assert(N <= Size); + if (LLVM_UNLIKELY(empty() || N == 0)) + return *this; + + unsigned NumWords = NumBitWords(Size); + assert(NumWords >= 1); + + wordShl(N / BITWORD_SIZE); + + unsigned BitDistance = N % BITWORD_SIZE; + if (BitDistance == 0) + return *this; + + // When the shift size is not a multiple of the word size, then we have + // a tricky situation where each word in succession needs to extract some + // of the bits from the previous word and or them into this word while + // shifting this word to make room for the new bits. This has to be done + // for every word in the array. This is similar to the algorithm outlined + // in operator>>=, but backwards. + + // Since we're shifting each word left, some bits will fall off the end + // of each word to the left, and empty space will be created on the right. + // The first word in the array will lose bits permanently, so starting at + // the end, work backwards shifting each word to the left, and OR'ing + // in the bits from the end of the next word to the beginning of the + // current word. + + // Example: + // Starting with {0xAABBCCDD, 0xEEFF0011, 0x22334455} and shifting left + // by 4 bits. + // Step 1: Word[2] <<= 4 ; 0x23344550 + // Step 2: Word[2] |= 0x0000000E ; 0x2334455E + // Step 3: Word[1] <<= 4 ; 0xEFF00110 + // Step 4: Word[1] |= 0x0000000A ; 0xEFF0011A + // Step 5: Word[0] <<= 4 ; 0xABBCCDD0 + // Result: { 0xABBCCDD0, 0xEFF0011A, 0x2334455E } + const BitWord Mask = maskLeadingOnes<BitWord>(BitDistance); + const unsigned RSH = BITWORD_SIZE - BitDistance; + + for (int I = NumWords - 1; I > 0; --I) { + Bits[I] <<= BitDistance; + Bits[I] |= (Bits[I - 1] & Mask) >> RSH; + } + Bits[0] <<= BitDistance; + clear_unused_bits(); + + return *this; + } + // Assignment operator. const BitVector &operator=(const BitVector &RHS) { if (this == &RHS) return *this; @@ -538,6 +639,54 @@ public: } private: + /// \brief Perform a logical left shift of \p Count words by moving everything + /// \p Count words to the right in memory. + /// + /// While confusing, words are stored from least significant at Bits[0] to + /// most significant at Bits[NumWords-1]. A logical shift left, however, + /// moves the current least significant bit to a higher logical index, and + /// fills the previous least significant bits with 0. Thus, we actually + /// need to move the bytes of the memory to the right, not to the left. + /// Example: + /// Words = [0xBBBBAAAA, 0xDDDDFFFF, 0x00000000, 0xDDDD0000] + /// represents a BitVector where 0xBBBBAAAA contain the least significant + /// bits. So if we want to shift the BitVector left by 2 words, we need to + /// turn this into 0x00000000 0x00000000 0xBBBBAAAA 0xDDDDFFFF by using a + /// memmove which moves right, not left. + void wordShl(uint32_t Count) { + if (Count == 0) + return; + + uint32_t NumWords = NumBitWords(Size); + + auto Src = ArrayRef<BitWord>(Bits, NumWords).drop_back(Count); + auto Dest = MutableArrayRef<BitWord>(Bits, NumWords).drop_front(Count); + + // Since we always move Word-sized chunks of data with src and dest both + // aligned to a word-boundary, we don't need to worry about endianness + // here. + std::memmove(Dest.begin(), Src.begin(), Dest.size() * sizeof(BitWord)); + std::memset(Bits, 0, Count * sizeof(BitWord)); + clear_unused_bits(); + } + + /// \brief Perform a logical right shift of \p Count words by moving those + /// words to the left in memory. See wordShl for more information. + /// + void wordShr(uint32_t Count) { + if (Count == 0) + return; + + uint32_t NumWords = NumBitWords(Size); + + auto Src = ArrayRef<BitWord>(Bits, NumWords).drop_front(Count); + auto Dest = MutableArrayRef<BitWord>(Bits, NumWords).drop_back(Count); + assert(Dest.size() == Src.size()); + + std::memmove(Dest.begin(), Src.begin(), Dest.size() * sizeof(BitWord)); + std::memset(Dest.end(), 0, Count * sizeof(BitWord)); + } + int next_unset_in_word(int WordIndex, BitWord Word) const { unsigned Result = WordIndex * BITWORD_SIZE + countTrailingOnes(Word); return Result < size() ? Result : -1; |