* Endian::little(x) little <-> native
* Endian::swap(x) big <-> little
*
- * BitIterator
- * Wrapper around an iterator over an integral type that iterates
- * over its underlying bits in MSb to LSb order
- *
- * findFirstSet(BitIterator begin, BitIterator end)
- * return a BitIterator pointing to the first 1 bit in [begin, end), or
- * end if all bits in [begin, end) are 0
- *
* @author Tudor Bosman (tudorb@fb.com)
*/
#pragma once
-#if !defined(__clang__) && !(defined(_MSC_VER) && (_MSC_VER < 1900))
-#define FOLLY_INTRINSIC_CONSTEXPR constexpr
-#else
-// GCC and MSVC 2015+ are the only compilers with
-// intrinsics constexpr.
+// MSVC does not support intrinsics constexpr
+#if defined(_MSC_VER)
#define FOLLY_INTRINSIC_CONSTEXPR const
+#else
+#define FOLLY_INTRINSIC_CONSTEXPR constexpr
#endif
#include <cassert>
#include <cinttypes>
#include <cstdint>
#include <cstring>
-#include <iterator>
#include <limits>
#include <type_traits>
-#include <boost/iterator/iterator_adaptor.hpp>
-
-#include <folly/Assume.h>
-#include <folly/Likely.h>
#include <folly/Portability.h>
-#include <folly/detail/BitIteratorDetail.h>
+#include <folly/lang/Assume.h>
#include <folly/portability/Builtins.h>
namespace folly {
#undef FB_GEN2
#undef FB_GEN1
-/**
- * Fast bit iteration facility.
- */
-
-
-template <class BaseIter> class BitIterator;
-template <class BaseIter>
-BitIterator<BaseIter> findFirstSet(BitIterator<BaseIter>,
- BitIterator<BaseIter>);
-/**
- * Wrapper around an iterator over an integer type that iterates
- * over its underlying bits in LSb to MSb order.
- *
- * BitIterator models the same iterator concepts as the base iterator.
- */
-template <class BaseIter>
-class BitIterator
- : public bititerator_detail::BitIteratorBase<BaseIter>::type {
- public:
- /**
- * Return the number of bits in an element of the underlying iterator.
- */
- static unsigned int bitsPerBlock() {
- return std::numeric_limits<
- typename std::make_unsigned<
- typename std::iterator_traits<BaseIter>::value_type
- >::type
- >::digits;
- }
-
- /**
- * Construct a BitIterator that points at a given bit offset (default 0)
- * in iter.
- */
- explicit BitIterator(const BaseIter& iter, size_t bitOff=0)
- : bititerator_detail::BitIteratorBase<BaseIter>::type(iter),
- bitOffset_(bitOff) {
- assert(bitOffset_ < bitsPerBlock());
- }
-
- size_t bitOffset() const {
- return bitOffset_;
- }
-
- void advanceToNextBlock() {
- bitOffset_ = 0;
- ++this->base_reference();
- }
-
- BitIterator& operator=(const BaseIter& other) {
- this->~BitIterator();
- new (this) BitIterator(other);
- return *this;
- }
-
- private:
- friend class boost::iterator_core_access;
- friend BitIterator findFirstSet<>(BitIterator, BitIterator);
-
- typedef bititerator_detail::BitReference<
- typename std::iterator_traits<BaseIter>::reference,
- typename std::iterator_traits<BaseIter>::value_type
- > BitRef;
-
- void advanceInBlock(size_t n) {
- bitOffset_ += n;
- assert(bitOffset_ < bitsPerBlock());
- }
-
- BitRef dereference() const {
- return BitRef(*this->base_reference(), bitOffset_);
- }
-
- void advance(ssize_t n) {
- size_t bpb = bitsPerBlock();
- ssize_t blocks = n / ssize_t(bpb);
- bitOffset_ += n % bpb;
- if (bitOffset_ >= bpb) {
- bitOffset_ -= bpb;
- ++blocks;
- }
- this->base_reference() += blocks;
- }
-
- void increment() {
- if (++bitOffset_ == bitsPerBlock()) {
- advanceToNextBlock();
- }
- }
-
- void decrement() {
- if (bitOffset_-- == 0) {
- bitOffset_ = bitsPerBlock() - 1;
- --this->base_reference();
- }
- }
-
- bool equal(const BitIterator& other) const {
- return (bitOffset_ == other.bitOffset_ &&
- this->base_reference() == other.base_reference());
- }
-
- ssize_t distance_to(const BitIterator& other) const {
- return ssize_t(
- (other.base_reference() - this->base_reference()) * bitsPerBlock() +
- other.bitOffset_ - bitOffset_);
- }
-
- size_t bitOffset_;
-};
-
-/**
- * Helper function, so you can write
- * auto bi = makeBitIterator(container.begin());
- */
-template <class BaseIter>
-BitIterator<BaseIter> makeBitIterator(const BaseIter& iter) {
- return BitIterator<BaseIter>(iter);
-}
-
-
-/**
- * Find first bit set in a range of bit iterators.
- * 4.5x faster than the obvious std::find(begin, end, true);
- */
-template <class BaseIter>
-BitIterator<BaseIter> findFirstSet(BitIterator<BaseIter> begin,
- BitIterator<BaseIter> end) {
- // shortcut to avoid ugly static_cast<>
- static const typename BaseIter::value_type one = 1;
-
- while (begin.base() != end.base()) {
- typename BaseIter::value_type v = *begin.base();
- // mask out the bits that don't matter (< begin.bitOffset)
- v &= ~((one << begin.bitOffset()) - 1);
- size_t firstSet = findFirstSet(v);
- if (firstSet) {
- --firstSet; // now it's 0-based
- assert(firstSet >= begin.bitOffset());
- begin.advanceInBlock(firstSet - begin.bitOffset());
- return begin;
- }
- begin.advanceToNextBlock();
- }
-
- // now begin points to the same block as end
- if (end.bitOffset() != 0) { // assume end is dereferenceable
- typename BaseIter::value_type v = *begin.base();
- // mask out the bits that don't matter (< begin.bitOffset)
- v &= ~((one << begin.bitOffset()) - 1);
- // mask out the bits that don't matter (>= end.bitOffset)
- v &= (one << end.bitOffset()) - 1;
- size_t firstSet = findFirstSet(v);
- if (firstSet) {
- --firstSet; // now it's 0-based
- assert(firstSet >= begin.bitOffset());
- begin.advanceInBlock(firstSet - begin.bitOffset());
- return begin;
- }
- }
-
- return end;
-}
-
template <class T, class Enable=void> struct Unaligned;
projects / folly.git / blobdiff