/*
- * Copyright 2014 Facebook, Inc.
+ * Copyright 2015 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
namespace folly { namespace compression {
-struct EliasFanoCompressedList {
- EliasFanoCompressedList() { }
+template <class Pointer>
+struct EliasFanoCompressedListBase {
+ EliasFanoCompressedListBase() = default;
+
+ template <class OtherPointer>
+ EliasFanoCompressedListBase(
+ const EliasFanoCompressedListBase<OtherPointer>& other)
+ : size(other.size),
+ numLowerBits(other.numLowerBits),
+ data(other.data),
+ skipPointers(reinterpret_cast<Pointer>(other.skipPointers)),
+ forwardPointers(reinterpret_cast<Pointer>(other.forwardPointers)),
+ lower(reinterpret_cast<Pointer>(other.lower)),
+ upper(reinterpret_cast<Pointer>(other.upper)) {
+ }
void free() {
- ::free(const_cast<unsigned char*>(lower.data()));
- ::free(const_cast<unsigned char*>(upper.data()));
- ::free(const_cast<unsigned char*>(skipPointers.data()));
- ::free(const_cast<unsigned char*>(forwardPointers.data()));
+ ::free(const_cast<unsigned char*>(data.data()));
+ }
+
+ size_t upperSize() const {
+ return data.end() - upper;
}
size_t size = 0;
uint8_t numLowerBits = 0;
- // WARNING: EliasFanoCompressedList has no ownership of
- // lower, upper, skipPointers and forwardPointers.
- // The 7 bytes following the last byte of lower and upper
- // sequences should be readable.
- folly::ByteRange lower;
- folly::ByteRange upper;
+ // WARNING: EliasFanoCompressedList has no ownership of data. The 7
+ // bytes following the last byte should be readable.
+ folly::Range<Pointer> data;
- folly::ByteRange skipPointers;
- folly::ByteRange forwardPointers;
+ Pointer skipPointers = nullptr;
+ Pointer forwardPointers = nullptr;
+ Pointer lower = nullptr;
+ Pointer upper = nullptr;
};
-// Version history:
-// In version 1 skip / forward pointers encoding has been changed,
-// so SkipValue = uint32_t is able to address up to ~4B elements,
-// instead of only ~2B.
+typedef EliasFanoCompressedListBase<const uint8_t*> EliasFanoCompressedList;
+typedef EliasFanoCompressedListBase<uint8_t*> MutableEliasFanoCompressedList;
+
template <class Value,
class SkipValue = size_t,
size_t kSkipQuantum = 0, // 0 = disabled
- size_t kForwardQuantum = 0, // 0 = disabled
- size_t kVersion = 0>
-struct EliasFanoEncoder {
+ size_t kForwardQuantum = 0> // 0 = disabled
+struct EliasFanoEncoderV2 {
static_assert(std::is_integral<Value>::value &&
std::is_unsigned<Value>::value,
"Value should be unsigned integral");
typedef Value ValueType;
typedef SkipValue SkipValueType;
+ struct Layout;
static constexpr size_t skipQuantum = kSkipQuantum;
static constexpr size_t forwardQuantum = kForwardQuantum;
- static constexpr size_t version = kVersion;
static uint8_t defaultNumLowerBits(size_t upperBound, size_t size) {
if (size == 0 || upperBound < size) {
if (begin == end) {
return EliasFanoCompressedList();
}
- EliasFanoEncoder encoder(end - begin, *(end - 1));
+ EliasFanoEncoderV2 encoder(end - begin, *(end - 1));
for (; begin != end; ++begin) {
encoder.add(*begin);
}
return encoder.finish();
}
- EliasFanoEncoder(size_t size, ValueType upperBound) {
- if (size == 0) {
- return;
- }
-
- uint8_t numLowerBits = defaultNumLowerBits(upperBound, size);
-
- // This is detail::writeBits56 limitation.
- numLowerBits = std::min<uint8_t>(numLowerBits, 56);
- CHECK_LT(numLowerBits, 8 * sizeof(Value)); // As we shift by numLowerBits.
-
- // WARNING: Current read/write logic assumes that the 7 bytes
- // following the last byte of lower and upper sequences are
- // readable (stored value doesn't matter and won't be changed),
- // so we allocate additional 7B, but do not include them in size
- // of returned value.
-
- // *** Lower bits.
- const size_t lowerSize = (numLowerBits * size + 7) / 8;
- if (lowerSize > 0) { // numLowerBits != 0
- lower_ = static_cast<unsigned char*>(calloc(lowerSize + 7, 1));
- }
-
- // *** Upper bits.
- // Upper bits are stored using unary delta encoding.
- // For example, (3 5 5 9) will be encoded as 1000011001000_2.
- const size_t upperSizeBits =
- (upperBound >> numLowerBits) + // Number of 0-bits to be stored.
- size; // 1-bits.
- const size_t upperSize = (upperSizeBits + 7) / 8;
- upper_ = static_cast<unsigned char*>(calloc(upperSize + 7, 1));
-
- // *** Skip pointers.
- // Store (1-indexed) position of every skipQuantum-th
- // 0-bit in upper bits sequence.
- size_t numSkipPointers = 0;
- /* static */ if (skipQuantum != 0) {
- /* static */ if (kVersion > 0) {
- CHECK_LT(size, std::numeric_limits<SkipValueType>::max());
- } else {
- CHECK_LT(upperSizeBits, std::numeric_limits<SkipValueType>::max());
- }
- // 8 * upperSize is used here instead of upperSizeBits, as that is
- // more serialization-friendly way (upperSizeBits isn't known outside of
- // this function, unlike upperSize; thus numSkipPointers could easily be
- // deduced from upperSize).
- numSkipPointers = (8 * upperSize - size) / (skipQuantum ?: 1);
- skipPointers_ = static_cast<SkipValueType*>(
- numSkipPointers == 0
- ? nullptr
- : calloc(numSkipPointers, sizeof(SkipValueType)));
- }
-
- // *** Forward pointers.
- // Store (1-indexed) position of every forwardQuantum-th
- // 1-bit in upper bits sequence.
- size_t numForwardPointers = 0;
- /* static */ if (forwardQuantum != 0) {
- /* static */ if (kVersion > 0) {
- CHECK_LT(upperBound >> numLowerBits,
- std::numeric_limits<SkipValueType>::max());
- } else {
- CHECK_LT(upperSizeBits, std::numeric_limits<SkipValueType>::max());
- }
-
- // '?: 1' is a workaround for false 'division by zero' compile-time error.
- numForwardPointers = size / (forwardQuantum ?: 1);
- forwardPointers_ = static_cast<SkipValueType*>(
- numForwardPointers == 0
- ? nullptr
- : malloc(numForwardPointers * sizeof(SkipValueType)));
- }
+ explicit EliasFanoEncoderV2(const MutableEliasFanoCompressedList& result)
+ : lower_(result.lower),
+ upper_(result.upper),
+ skipPointers_(reinterpret_cast<SkipValueType*>(
+ result.skipPointers)),
+ forwardPointers_(reinterpret_cast<SkipValueType*>(
+ result.forwardPointers)),
+ result_(result) {
+ }
- // *** Result.
- result_.size = size;
- result_.numLowerBits = numLowerBits;
- result_.lower.reset(lower_, lowerSize);
- result_.upper.reset(upper_, upperSize);
- result_.skipPointers.reset(
- reinterpret_cast<unsigned char*>(skipPointers_),
- numSkipPointers * sizeof(SkipValueType));
- result_.forwardPointers.reset(
- reinterpret_cast<unsigned char*>(forwardPointers_),
- numForwardPointers * sizeof(SkipValueType));
+ EliasFanoEncoderV2(size_t size, ValueType upperBound)
+ : EliasFanoEncoderV2(
+ Layout::fromUpperBoundAndSize(upperBound, size).allocList()) {
}
void add(ValueType value) {
/* static */ if (skipQuantum != 0) {
while ((skipPointersSize_ + 1) * skipQuantum <= upperBits) {
- /* static */ if (kVersion > 0) {
- // Since version 1, just the number of preceding 1-bits is stored.
- skipPointers_[skipPointersSize_] = size_;
- } else {
- skipPointers_[skipPointersSize_] =
- size_ + (skipPointersSize_ + 1) * skipQuantum;
- }
- ++skipPointersSize_;
+ // Store the number of preceding 1-bits.
+ skipPointers_[skipPointersSize_++] = size_;
}
}
/* static */ if (forwardQuantum != 0) {
if ((size_ + 1) % forwardQuantum == 0) {
const auto pos = size_ / forwardQuantum;
- /* static */ if (kVersion > 0) {
- // Since version 1, just the number of preceding 0-bits is stored.
- forwardPointers_[pos] = upperBits;
- } else {
- forwardPointers_[pos] = upperBits + size_ + 1;
- }
+ // Store the number of preceding 0-bits.
+ forwardPointers_[pos] = upperBits;
}
}
EliasFanoCompressedList result_;
};
+template <class Value,
+ class SkipValue,
+ size_t kSkipQuantum,
+ size_t kForwardQuantum>
+struct EliasFanoEncoderV2<Value,
+ SkipValue,
+ kSkipQuantum,
+ kForwardQuantum>::Layout {
+ static Layout fromUpperBoundAndSize(size_t upperBound, size_t size) {
+ // numLowerBits can be at most 56 because of detail::writeBits56.
+ const uint8_t numLowerBits = std::min(defaultNumLowerBits(upperBound,
+ size),
+ uint8_t(56));
+ // *** Upper bits.
+ // Upper bits are stored using unary delta encoding.
+ // For example, (3 5 5 9) will be encoded as 1000011001000_2.
+ const size_t upperSizeBits =
+ (upperBound >> numLowerBits) + // Number of 0-bits to be stored.
+ size; // 1-bits.
+ const size_t upper = (upperSizeBits + 7) / 8;
+
+ // *** Validity checks.
+ // Shift by numLowerBits must be valid.
+ CHECK_LT(numLowerBits, 8 * sizeof(Value));
+ CHECK_LT(size, std::numeric_limits<SkipValueType>::max());
+ CHECK_LT(upperBound >> numLowerBits,
+ std::numeric_limits<SkipValueType>::max());
+
+ return fromInternalSizes(numLowerBits, upper, size);
+ }
+
+ static Layout fromInternalSizes(uint8_t numLowerBits,
+ size_t upper,
+ size_t size) {
+ Layout layout;
+ layout.size = size;
+ layout.numLowerBits = numLowerBits;
+
+ layout.lower = (numLowerBits * size + 7) / 8;
+ layout.upper = upper;
+
+ // *** Skip pointers.
+ // Store (1-indexed) position of every skipQuantum-th
+ // 0-bit in upper bits sequence.
+ /* static */ if (skipQuantum != 0) {
+ // 8 * upper is used here instead of upperSizeBits, as that is
+ // more serialization-friendly way (upperSizeBits doesn't need
+ // to be known by this function, unlike upper).
+
+ // '?: 1' is a workaround for false 'division by zero'
+ // compile-time error.
+ size_t numSkipPointers = (8 * upper - size) / (skipQuantum ?: 1);
+ layout.skipPointers = numSkipPointers * sizeof(SkipValueType);
+ }
+
+ // *** Forward pointers.
+ // Store (1-indexed) position of every forwardQuantum-th
+ // 1-bit in upper bits sequence.
+ /* static */ if (forwardQuantum != 0) {
+ size_t numForwardPointers = size / (forwardQuantum ?: 1);
+ layout.forwardPointers = numForwardPointers * sizeof(SkipValueType);
+ }
+
+ return layout;
+ }
+
+ size_t bytes() const {
+ return lower + upper + skipPointers + forwardPointers;
+ }
+
+ template <typename Range>
+ EliasFanoCompressedListBase<typename Range::iterator>
+ openList(Range& buf) const {
+ EliasFanoCompressedListBase<typename Range::iterator> result;
+ result.size = size;
+ result.numLowerBits = numLowerBits;
+ result.data = buf.subpiece(0, bytes());
+
+ auto advance = [&] (size_t n) {
+ auto begin = buf.data();
+ buf.advance(n);
+ return begin;
+ };
+
+ result.skipPointers = advance(skipPointers);
+ result.forwardPointers = advance(forwardPointers);
+ result.lower = advance(lower);
+ result.upper = advance(upper);
+
+ return result;
+ }
+
+ MutableEliasFanoCompressedList allocList() const {
+ uint8_t* buf = nullptr;
+ // WARNING: Current read/write logic assumes that the 7 bytes
+ // following the last byte of lower and upper sequences are
+ // readable (stored value doesn't matter and won't be changed),
+ // so we allocate additional 7B, but do not include them in size
+ // of returned value.
+ if (size > 0) {
+ buf = static_cast<uint8_t*>(calloc(bytes() + 7, 1));
+ }
+ folly::MutableByteRange bufRange(buf, bytes());
+ return openList(bufRange);
+ }
+
+ size_t size = 0;
+ uint8_t numLowerBits = 0;
+
+ // Sizes in bytes.
+ size_t lower = 0;
+ size_t upper = 0;
+ size_t skipPointers = 0;
+ size_t forwardPointers = 0;
+};
+
// NOTE: It's recommended to compile EF coding with -msse4.2, starting
// with Nehalem, Intel CPUs support POPCNT instruction and gcc will emit
// it for __builtin_popcountll intrinsic.
typedef typename Encoder::ValueType ValueType;
explicit UpperBitsReader(const EliasFanoCompressedList& list)
- : forwardPointers_(list.forwardPointers.data()),
- skipPointers_(list.skipPointers.data()),
- start_(list.upper.data()) {
+ : forwardPointers_(list.forwardPointers),
+ skipPointers_(list.skipPointers),
+ start_(list.upper) {
reset();
}
folly::loadUnaligned<SkipValueType>(
forwardPointers_ + (steps - 1) * sizeof(SkipValueType));
- /* static */ if (Encoder::version > 0) {
- reposition(dest + steps * q);
- } else {
- reposition(dest);
- }
+ reposition(dest + steps * q);
n = position_ + 1 - steps * q; // n is > 0.
- // correct inner_ will be set at the end.
+ // Correct inner_ will be set at the end.
}
size_t cnt;
folly::loadUnaligned<SkipValueType>(
skipPointers_ + (steps - 1) * sizeof(SkipValueType));
- /* static */ if (Encoder::version > 0) {
- reposition(dest + q * steps);
- position_ = dest - 1;
- } else {
- reposition(dest);
- position_ = dest - q * steps - 1;
- }
+ reposition(dest + q * steps);
+ position_ = dest - 1;
+
// Correct inner_ and value_ will be set during the next()
// call at the end.
lastValue_ = 0;
return;
}
- ValueType lastUpperValue = 8 * list_.upper.size() - list_.size;
- auto it = list_.upper.end() - 1;
+ ValueType lastUpperValue = 8 * list_.upperSize() - list_.size;
+ auto it = list_.upper + list_.upperSize() - 1;
DCHECK_NE(*it, 0);
lastUpperValue -= 8 - folly::findLastSet(*it);
lastValue_ = readLowerPart(list_.size - 1) |
}
bool next() {
- if (UNLIKELY(progress_ == list_.size)) {
- value_ = std::numeric_limits<ValueType>::max();
- return false;
+ if (UNLIKELY(progress_ >= list_.size)) {
+ return setDone();
}
value_ = readLowerPart(progress_) |
(upper_.next() << list_.numLowerBits);
return true;
}
- progress_ = list_.size;
- value_ = std::numeric_limits<ValueType>::max();
- return false;
+ return setDone();
}
bool skipTo(ValueType value) {
if (value <= value_) {
return true;
} else if (value > lastValue_) {
- progress_ = list_.size;
- value_ = std::numeric_limits<ValueType>::max();
- return false;
+ return setDone();
}
size_t upperValue = (value >> list_.numLowerBits);
reset();
return true;
}
- progress_ = list_.size;
- value_ = std::numeric_limits<ValueType>::max();
- return false;
+ return setDone();
}
- ValueType jumpTo(ValueType value) {
+ bool jumpTo(ValueType value) {
if (value <= 0) {
reset();
return true;
} else if (value > lastValue_) {
- progress_ = list_.size;
- value_ = std::numeric_limits<ValueType>::max();
- return false;
+ return setDone();
}
upper_.jumpToNext(value >> list_.numLowerBits);
ValueType value() const { return value_; }
private:
+ bool setDone() {
+ value_ = std::numeric_limits<ValueType>::max();
+ progress_ = list_.size + 1;
+ return false;
+ }
+
ValueType readLowerPart(size_t i) const {
DCHECK_LT(i, list_.size);
const size_t pos = i * list_.numLowerBits;
- const unsigned char* ptr = list_.lower.data() + (pos / 8);
+ const unsigned char* ptr = list_.lower + (pos / 8);
const uint64_t ptrv = folly::loadUnaligned<uint64_t>(ptr);
return lowerMask_ & (ptrv >> (pos % 8));
}
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