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Commit dabc9802 authored by Giuseppe Ottaviano's avatar Giuseppe Ottaviano Committed by Facebook GitHub Bot
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Revert D22211304: Eliminate need for reading upper bound at construction. 

Differential Revision:
D22211304 (https://github.com/facebook/folly/commit/c9c5564232aaffbc0f1d3807b21bb2cd60ec4d2d)

Original commit changeset: 0dbe904c9fd8

fbshipit-source-id: 49cf24dab4f91fcebf9dc5a2db66d23683fcaa37
parent e739084e
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Showing with 103 additions and 180 deletions
folly/experimental/EliasFanoCoding.h
View file @ dabc9802
......@@ -24,11 +24,9 @@
#pragma once
#include <algorithm>
#include <cstddef>
#include <cstdlib>
#include <limits>
#include <type_traits>
#include <utility>
#include <folly/Likely.h>
#include <folly/Portability.h>
......@@ -356,24 +354,18 @@ struct EliasFanoEncoderV2<
namespace detail {
template <
class Encoder,
class Instructions,
class SizeType,
bool kUnchecked = false>
template <class Encoder, class Instructions, class SizeType>
class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
SkipPointers<Encoder::skipQuantum> {
using SkipValueType = typename Encoder::SkipValueType;
typedef typename Encoder::SkipValueType SkipValueType;
public:
using ValueType = typename Encoder::ValueType;
typedef typename Encoder::ValueType ValueType;
explicit UpperBitsReader(const typename Encoder::CompressedList& list)
: ForwardPointers<Encoder::forwardQuantum>(list.forwardPointers),
SkipPointers<Encoder::skipQuantum>(list.skipPointers),
start_(list.upper),
size_(list.size),
upperBound_(8 * list.upperSizeBytes - size_) {
start_(list.upper) {
reset();
}
......@@ -388,23 +380,11 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
FOLLY_ALWAYS_INLINE SizeType position() const {
return position_;
}
FOLLY_ALWAYS_INLINE ValueType value() const {
return value_;
}
FOLLY_ALWAYS_INLINE bool valid() const {
return position() < size();
}
FOLLY_ALWAYS_INLINE SizeType size() const {
return size_;
}
FOLLY_ALWAYS_INLINE bool previous() {
if (!kUnchecked && UNLIKELY(position() == 0)) {
return false;
}
FOLLY_ALWAYS_INLINE ValueType previous() {
size_t inner;
block_t block;
getPreviousInfo(block, inner, outer_);
......@@ -414,12 +394,7 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
return setValue(inner);
}
// Returns `true` if the next position is within bounds.
FOLLY_ALWAYS_INLINE bool next() {
if (!kUnchecked && UNLIKELY(position() + 1 >= size())) {
return setDone();
}
FOLLY_ALWAYS_INLINE ValueType next() {
// Skip to the first non-zero block.
while (block_ == 0) {
outer_ += sizeof(block_t);
......@@ -429,14 +404,12 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
++position_;
size_t inner = Instructions::ctz(block_);
block_ = Instructions::blsr(block_);
return setValue(inner);
}
FOLLY_ALWAYS_INLINE bool skip(SizeType n) {
FOLLY_ALWAYS_INLINE ValueType skip(SizeType n) {
DCHECK_GT(n, 0);
if (!kUnchecked && UNLIKELY(position_ + n >= size())) {
return setDone();
}
position_ += n; // n 1-bits will be read.
......@@ -462,18 +435,15 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
DCHECK_GT(n, 0);
size_t inner = select64<Instructions>(block_, n - 1);
block_ &= (block_t(-1) << inner) << 1;
return setValue(inner);
}
// Skip to the first element that is >= v and located *after* the current
// one (so even if current value equals v, position will be increased by 1).
FOLLY_ALWAYS_INLINE bool skipToNext(ValueType v) {
FOLLY_ALWAYS_INLINE ValueType skipToNext(ValueType v) {
DCHECK_GE(v, value_);
if (!kUnchecked && UNLIKELY(v > upperBound_)) {
return setDone();
}
// Use skip pointer.
if (Encoder::skipQuantum > 0 &&
UNLIKELY(v >= value_ + Encoder::skipQuantum)) {
......@@ -481,12 +451,6 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
const size_t dest = folly::loadUnaligned<SkipValueType>(
this->skipPointers_ + (steps - 1) * sizeof(SkipValueType));
DCHECK_LE(dest, size());
// Check if we've reached the end.
if (!kUnchecked && UNLIKELY(dest == size())) {
return setDone();
}
reposition(dest + Encoder::skipQuantum * steps);
position_ = dest - 1;
......@@ -506,7 +470,6 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
skip -= cnt;
position_ += kBitsPerBlock - cnt;
outer_ += sizeof(block_t);
DCHECK_LT(outer_, (static_cast<size_t>(upperBound_) + size()) / 8);
block_ = folly::loadUnaligned<block_t>(start_ + outer_);
}
......@@ -516,24 +479,17 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
block_ &= block_t(-1) << inner;
}
DCHECK_LT(position() + 1, size() + 1);
return next();
next();
return value_;
}
/**
* Try to prepare to skip to value. This is a constant-time operation
* that will attempt to prefetch memory required for a subsequent
* skipTo(value) call if the value to skip to is within this list.
* Prepare to skip to `value`. This is a constant-time operation that will
* prefetch memory required for a `skipTo(value)` call.
*
* Returns:
* {true, position of the reader} if the skip is valid,
* {false, size()} otherwise.
* @return position of reader
*/
FOLLY_ALWAYS_INLINE std::pair<bool, SizeType> prepareSkipTo(
ValueType v) const {
if (!kUnchecked && UNLIKELY(v > upperBound_)) {
return std::make_pair(false, size());
}
FOLLY_ALWAYS_INLINE SizeType prepareSkipTo(ValueType v) const {
auto position = position_;
if (Encoder::skipQuantum > 0 && v >= value_ + Encoder::skipQuantum) {
......@@ -542,12 +498,6 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
const size_t dest = folly::loadUnaligned<SkipValueType>(
this->skipPointers_ + (steps - 1) * sizeof(SkipValueType));
DCHECK_LE(dest, size());
// Check if we're going out of bounds.
if (!kUnchecked && UNLIKELY(dest == size())) {
return std::make_pair(false, size());
}
position = dest - 1;
outer = (dest + Encoder::skipQuantum * steps) / 8;
......@@ -562,7 +512,7 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
__builtin_prefetch(addr + kCacheLineSize);
}
return std::make_pair(true, position);
return position;
}
FOLLY_ALWAYS_INLINE ValueType previousValue() const {
......@@ -584,15 +534,14 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
return (start_[bitPos / 8] & (1 << (bitPos % 8))) == 0;
}
FOLLY_ALWAYS_INLINE bool setDone() {
position_ = size_;
return false;
FOLLY_ALWAYS_INLINE void setDone(SizeType endPos) {
position_ = endPos;
}
private:
FOLLY_ALWAYS_INLINE bool setValue(size_t inner) {
FOLLY_ALWAYS_INLINE ValueType setValue(size_t inner) {
value_ = static_cast<ValueType>(8 * outer_ + inner - position_);
return true;
return value_;
}
FOLLY_ALWAYS_INLINE void reposition(SizeType dest) {
......@@ -624,8 +573,6 @@ class UpperBitsReader : ForwardPointers<Encoder::forwardQuantum>,
}
const unsigned char* const start_;
const SizeType size_; // Size of the list.
const ValueType upperBound_; // Upper bound of values in this list.
block_t block_;
SizeType position_; // Index of current value (= #reads - 1).
OuterType outer_; // Outer offset: number of consumed bytes in upper.
......@@ -651,8 +598,24 @@ class EliasFanoReader {
typedef typename Encoder::ValueType ValueType;
explicit EliasFanoReader(const typename Encoder::CompressedList& list)
: upper_(list), lower_(list.lower), numLowerBits_(list.numLowerBits) {
: upper_(list),
lower_(list.lower),
size_(list.size),
numLowerBits_(list.numLowerBits) {
DCHECK(Instructions::supported());
// To avoid extra branching during skipTo() while reading
// upper sequence we need to know the last element.
// If kUnchecked == true, we do not check that skipTo() is called
// within the bounds, so we can avoid initializing lastValue_.
if (kUnchecked || UNLIKELY(list.size == 0)) {
lastValue_ = 0;
return;
}
ValueType lastUpperValue = ValueType(8 * list.upperSizeBytes - size_);
auto it = list.upper + list.upperSizeBytes - 1;
DCHECK_NE(*it, 0);
lastUpperValue -= 8 - folly::findLastSet(*it);
lastValue_ = readLowerPart(size_ - 1) | (lastUpperValue << numLowerBits_);
}
void reset() {
......@@ -661,20 +624,24 @@ class EliasFanoReader {
}
bool previous() {
if (LIKELY(upper_.previous())) {
setCurrentValue();
return true;
if (!kUnchecked && UNLIKELY(position() == 0)) {
reset();
return false;
}
reset();
return false;
upper_.previous();
value_ =
readLowerPart(upper_.position()) | (upper_.value() << numLowerBits_);
return true;
}
bool next() {
if (LIKELY(upper_.next())) {
setCurrentValue();
return true;
if (!kUnchecked && UNLIKELY(position() + 1 >= size_)) {
return setDone();
}
return setDone();
upper_.next();
value_ =
readLowerPart(upper_.position()) | (upper_.value() << numLowerBits_);
return true;
}
/**
......@@ -686,11 +653,14 @@ class EliasFanoReader {
return valid();
}
if (!upper_.skip(n)) {
return setDone();
if (kUnchecked || LIKELY(position() + n < size_)) {
upper_.skip(n);
value_ =
readLowerPart(upper_.position()) | (upper_.value() << numLowerBits_);
return true;
}
setCurrentValue();
return true;
return setDone();
}
/**
......@@ -701,25 +671,18 @@ class EliasFanoReader {
bool skipTo(ValueType value) {
if (value != kInvalidValue) {
DCHECK_GE(value + 1, value_ + 1);
if (UNLIKELY(value == value_)) {
return true;
}
}
ValueType upperValue = value >> numLowerBits_;
if (UNLIKELY(!upper_.skipToNext(upperValue))) {
// The value is beyond the last value in the list.
if (!kUnchecked && UNLIKELY(value > lastValue_)) {
return setDone();
} else if (UNLIKELY(value == value_)) {
return true;
}
do {
setCurrentValue();
if (LIKELY(value_ >= value)) {
return true;
}
} while (LIKELY(upper_.next()));
return setDone();
ValueType upperValue = value >> numLowerBits_;
upper_.skipToNext(upperValue);
iterateTo(value);
return true;
}
/**
......@@ -730,21 +693,19 @@ class EliasFanoReader {
// Also works when value_ == kInvalidValue.
if (value != kInvalidValue) {
DCHECK_GE(value + 1, value_ + 1);
if (UNLIKELY(value == value_)) {
return;
}
}
if ((!kUnchecked && value > lastValue_) || (value == value_)) {
return;
}
// Do minimal computation required to prefetch address used in
// `readLowerPart()`.
ValueType upperValue = (value >> numLowerBits_);
const auto skipDetails = upper_.prepareSkipTo(upperValue);
// If we have a valid skip position, prefetch the lower bits for it.
if (LIKELY(skipDetails.first)) {
const auto addr = lower_ + (skipDetails.second * numLowerBits_ / 8);
__builtin_prefetch(addr);
__builtin_prefetch(addr + kCacheLineSize);
}
const auto upperPosition = upper_.prepareSkipTo(upperValue);
const auto addr = lower_ + (upperPosition * numLowerBits_ / 8);
__builtin_prefetch(addr);
__builtin_prefetch(addr + kCacheLineSize);
}
/**
......@@ -752,11 +713,11 @@ class EliasFanoReader {
* false if n >= size().
*/
bool jump(SizeType n) {
if (n + 1 < position() + 1) { // Also works if position() == -1.
if (n + 1 < upper_.position() + 1) { // Also works if position() == -1.
reset();
n += 1; // Initial position is -1.
} else {
n -= position();
n -= upper_.position();
}
return skip(n);
}
......@@ -777,7 +738,7 @@ class EliasFanoReader {
// We might be in the middle of a run, iterate backwards to the beginning.
auto valueLower = Instructions::bzhi(value_, numLowerBits_);
while (!upper_.isAtBeginningOfRun() &&
readLowerPart(position() - 1) == valueLower) {
readLowerPart(upper_.position() - 1) == valueLower) {
upper_.previous();
}
return true;
......@@ -792,15 +753,20 @@ class EliasFanoReader {
return skipTo(value);
}
ValueType lastValue() const {
CHECK(!kUnchecked);
return lastValue_;
}
ValueType previousValue() const {
DCHECK_GT(position(), 0);
DCHECK_LT(position(), size());
return readLowerPart(position() - 1) |
return readLowerPart(upper_.position() - 1) |
(upper_.previousValue() << numLowerBits_);
}
SizeType size() const {
return upper_.size();
return size_;
}
bool valid() const {
......@@ -821,27 +787,37 @@ class EliasFanoReader {
FOLLY_ALWAYS_INLINE bool setDone() {
value_ = kInvalidValue;
return upper_.setDone();
}
FOLLY_ALWAYS_INLINE void setCurrentValue() {
value_ = readLowerPart(position()) | (upper_.value() << numLowerBits_);
upper_.setDone(size_);
return false;
}
FOLLY_ALWAYS_INLINE ValueType readLowerPart(SizeType i) const {
DCHECK_LT(i, size());
DCHECK_LT(i, size_);
const size_t pos = i * numLowerBits_;
const unsigned char* ptr = lower_ + (pos / 8);
const uint64_t ptrv = folly::loadUnaligned<uint64_t>(ptr);
// This removes the branch in the fallback implementation of
// bzhi. The condition is verified at encoding time.
folly::assume(numLowerBits_ < sizeof(ValueType) * 8);
assume(numLowerBits_ < sizeof(ValueType) * 8);
return Instructions::bzhi(ptrv >> (pos % 8), numLowerBits_);
}
detail::UpperBitsReader<Encoder, Instructions, SizeType, kUnchecked> upper_;
FOLLY_ALWAYS_INLINE void iterateTo(ValueType value) {
while (true) {
value_ =
readLowerPart(upper_.position()) | (upper_.value() << numLowerBits_);
if (LIKELY(value_ >= value)) {
break;
}
upper_.next();
}
}
detail::UpperBitsReader<Encoder, Instructions, SizeType> upper_;
const uint8_t* lower_;
SizeType size_;
ValueType value_ = kInvalidValue;
ValueType lastValue_;
uint8_t numLowerBits_;
};
......
folly/experimental/test/CodingTestUtils.h
View file @ dabc9802
......@@ -35,11 +35,6 @@
namespace folly {
namespace compression {
template <typename ValueType, class List>
folly::Optional<std::size_t> getUniverseUpperBound(const List& /* list */) {
return folly::none;
}
template <class URNG>
std::vector<uint64_t> generateRandomList(
size_t n,
......@@ -273,16 +268,6 @@ void testSkipTo(const std::vector<uint64_t>& data, const List& list) {
EXPECT_EQ(reader.position(), reader.size());
EXPECT_FALSE(reader.next());
}
// Skip past the last element and before the upperBound.
using ValueType = typename Reader::ValueType;
if (const auto upperBound = getUniverseUpperBound<ValueType>(list);
upperBound && *upperBound != data.back()) {
Reader reader(list);
EXPECT_FALSE(reader.skipTo(*upperBound));
EXPECT_FALSE(reader.valid());
EXPECT_EQ(reader.position(), reader.size());
EXPECT_FALSE(reader.next());
}
}
template <class Reader, class List>
......@@ -377,19 +362,9 @@ void testEmpty() {
}
}
// `upperBoundExtension` is required to inject additional 0-blocks
// at the end of the list. This allows us to test lists with a large gap between
// last element and universe upper bound, to exercise bounds-checking when
// skipping past the last element
template <class Reader, class Encoder>
void testAll(
const std::vector<uint64_t>& data,
uint64_t upperBoundExtension = 0) {
Encoder encoder(data.size(), data.back() + upperBoundExtension);
for (const auto value : data) {
encoder.add(value);
}
auto list = encoder.finish();
void testAll(const std::vector<uint64_t>& data) {
auto list = Encoder::encode(data.begin(), data.end());
testNext<Reader>(data, list);
testSkip<Reader>(data, list);
testSkipTo<Reader>(data, list);
......
folly/experimental/test/EliasFanoCodingTest.cpp
View file @ dabc9802
......@@ -21,32 +21,11 @@
#include <vector>
#include <folly/Benchmark.h>
#include <folly/Optional.h>
#include <folly/Random.h>
#include <folly/experimental/EliasFanoCoding.h>
#include <folly/experimental/Select64.h>
#include <folly/experimental/test/CodingTestUtils.h>
#include <folly/init/Init.h>
namespace folly {
namespace compression {
// Overload to help CodingTestUtils retrieve the universe upperbound
// of the list for certain test cases.
template <typename ValueType, typename T>
folly::Optional<std::size_t> getUniverseUpperBound(
const EliasFanoCompressedListBase<T>& list) {
constexpr ValueType maxUpperValue = std::numeric_limits<ValueType>::max();
const ValueType maxUpperBits = maxUpperValue >> list.numLowerBits;
const ValueType upperBitsUniverse = std::min(
static_cast<ValueType>(8 * list.upperSizeBytes - list.size),
maxUpperBits);
return (upperBitsUniverse << list.numLowerBits) |
((1 << list.numLowerBits) - 1);
}
} // namespace compression
} // namespace folly
using namespace folly::compression;
namespace {
......@@ -135,13 +114,6 @@ class EliasFanoCodingTest : public ::testing::Test {
// max() cannot be read, as it is assumed an invalid value.
// TODO(ott): It should be possible to lift this constraint.
testAll<Reader, Encoder>({0, 1, std::numeric_limits<uint32_t>::max() - 1});
// Test data with additional trailing 0s in the upperBits by extending
// the upper bound.
constexpr uint64_t minUpperBoundExtension = 2;
constexpr uint64_t maxUpperBoundExtension = 1024;
testAll<Reader, Encoder>(
generateRandomList(100 * 1000, 10 * 1000 * 1000),
folly::Random::rand32(minUpperBoundExtension, maxUpperBoundExtension));
}
};
......
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