/*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* "Quasi-succinct indices" (arxiv:1206.4300).
*/
-#ifndef FOLLY_EXPERIMENTAL_ELIAS_FANO_CODING_H
-#define FOLLY_EXPERIMENTAL_ELIAS_FANO_CODING_H
+#pragma once
+#include <algorithm>
#include <cstdlib>
#include <limits>
#include <type_traits>
#include <folly/experimental/Select64.h>
#include <glog/logging.h>
-#ifndef __GNUC__
-#error EliasFanoCoding.h requires GCC
-#endif
-
#if !FOLLY_X64
#error EliasFanoCoding.h requires x86_64
#endif
-#if __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__
-#error EliasFanoCoding.h requires little endianness
-#endif
-
namespace folly { namespace compression {
+static_assert(kIsLittleEndian, "EliasFanoCoding.h requires little endianness");
+
template <class Pointer>
struct EliasFanoCompressedListBase {
EliasFanoCompressedListBase() = default;
return ::free(data.data());
}
- size_t upperSize() const { return data.end() - upper; }
+ size_t upperSize() const {
+ return size_t(data.end() - upper);
+ }
size_t size = 0;
uint8_t numLowerBits = 0;
static constexpr size_t forwardQuantum = kForwardQuantum;
static uint8_t defaultNumLowerBits(size_t upperBound, size_t size) {
- if (size == 0 || upperBound < size) {
+ if (UNLIKELY(size == 0 || upperBound < size)) {
return 0;
}
- // floor(log(upperBound / size));
- return folly::findLastSet(upperBound / size) - 1;
+ // Result that should be returned is "floor(log(upperBound / size))".
+ // In order to avoid expensive division, we rely on
+ // "floor(a) - floor(b) - 1 <= floor(a - b) <= floor(a) - floor(b)".
+ // Assuming "candidate = floor(log(upperBound)) - floor(log(upperBound))",
+ // then result is either "candidate - 1" or "candidate".
+ auto candidate = folly::findLastSet(upperBound) - folly::findLastSet(size);
+ // NOTE: As size != 0, "candidate" is always < 64.
+ return (size > (upperBound >> candidate)) ? candidate - 1 : candidate;
}
// Requires: input range (begin, end) is sorted (encoding
if (begin == end) {
return MutableCompressedList();
}
- EliasFanoEncoderV2 encoder(end - begin, *(end - 1));
+ EliasFanoEncoderV2 encoder(size_t(end - begin), *(end - 1));
for (; begin != end; ++begin) {
encoder.add(*begin);
}
forwardPointers_(reinterpret_cast<SkipValueType*>(
result.forwardPointers)),
result_(result) {
- memset(result.data.data(), 0, result.data.size());
+ std::fill(result.data.begin(), result.data.end(), 0);
}
EliasFanoEncoderV2(size_t size, ValueType upperBound)
/* static */ if (skipQuantum != 0) {
while ((skipPointersSize_ + 1) * skipQuantum <= upperBits) {
// Store the number of preceding 1-bits.
- skipPointers_[skipPointersSize_++] = size_;
+ skipPointers_[skipPointersSize_++] = SkipValue(size_);
}
}
/* static */ if (forwardQuantum != 0) {
if ((size_ + 1) % forwardQuantum == 0) {
- const auto pos = size_ / forwardQuantum;
+ const auto k = size_ / forwardQuantum;
// Store the number of preceding 0-bits.
- forwardPointers_[pos] = upperBits;
+ forwardPointers_[k] = upperBits;
}
}
// 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);
+ size_t numSkipPointers = (8 * upper - size) / skipQuantum;
layout.skipPointers = numSkipPointers * sizeof(SkipValueType);
}
// Store (1-indexed) position of every forwardQuantum-th
// 1-bit in upper bits sequence.
/* static */ if (forwardQuantum != 0) {
- size_t numForwardPointers = size / (forwardQuantum ?: 1);
+ size_t numForwardPointers = size / forwardQuantum;
layout.forwardPointers = numForwardPointers * sizeof(SkipValueType);
}
void reset() {
block_ = start_ != nullptr ? folly::loadUnaligned<block_t>(start_) : 0;
outer_ = 0;
- inner_ = -1;
- position_ = -1;
+ inner_ = std::numeric_limits<size_t>::max();
+ position_ = std::numeric_limits<size_t>::max();
value_ = 0;
}
}
++position_;
- inner_ = Instructions::ctz(block_);
+ inner_ = size_t(Instructions::ctz(block_));
block_ = Instructions::blsr(block_);
return setValue();
// Use forward pointer.
if (Encoder::forwardQuantum > 0 && n > Encoder::forwardQuantum) {
- // Workaround to avoid 'division by zero' compile-time error.
- constexpr size_t q = Encoder::forwardQuantum ?: 1;
-
- const size_t steps = position_ / q;
+ const size_t steps = position_ / Encoder::forwardQuantum;
const size_t dest =
folly::loadUnaligned<SkipValueType>(
forwardPointers_ + (steps - 1) * sizeof(SkipValueType));
- reposition(dest + steps * q);
- n = position_ + 1 - steps * q; // n is > 0.
+ reposition(dest + steps * Encoder::forwardQuantum);
+ n = position_ + 1 - steps * Encoder::forwardQuantum; // n is > 0.
// Correct inner_ will be set at the end.
}
// Use skip pointer.
if (Encoder::skipQuantum > 0 && v >= value_ + Encoder::skipQuantum) {
- // Workaround to avoid 'division by zero' compile-time error.
- constexpr size_t q = Encoder::skipQuantum ?: 1;
-
- const size_t steps = v / q;
+ const size_t steps = v / Encoder::skipQuantum;
const size_t dest =
folly::loadUnaligned<SkipValueType>(
skipPointers_ + (steps - 1) * sizeof(SkipValueType));
- reposition(dest + q * steps);
+ reposition(dest + Encoder::skipQuantum * steps);
position_ = dest - 1;
// Correct inner_ and value_ will be set during the next()
if (Encoder::forwardQuantum == 0 || n <= Encoder::forwardQuantum) {
reset();
} else {
- position_ = -1; // Avoid reading the head, skip() will reposition.
+ position_ = size_t(-1); // Avoid reading the head, skip() will reposition.
}
return skip(n);
}
block &= (block_t(1) << inner_) - 1;
while (UNLIKELY(block == 0)) {
- DCHECK_GE(outer, sizeof(block_t));
- outer -= sizeof(block_t);
+ DCHECK_GT(outer, 0);
+ outer -= std::min(sizeof(block_t), outer);
block = folly::loadUnaligned<block_t>(start_ + outer);
}
lastValue_ = 0;
return;
}
- ValueType lastUpperValue = 8 * list.upperSize() - size_;
+ ValueType lastUpperValue = ValueType(8 * list.upperSize() - size_);
auto it = list.upper + list.upperSize() - 1;
DCHECK_NE(*it, 0);
lastUpperValue -= 8 - folly::findLastSet(*it);
return true;
}
- size_t upperValue = (value >> numLowerBits_);
- size_t upperSkip = upperValue - upper_.value();
+ ValueType upperValue = (value >> numLowerBits_);
+ ValueType upperSkip = upperValue - upper_.value();
// The average density of ones in upper bits is 1/2.
// LIKELY here seems to make things worse, even for small skips.
if (upperSkip < 2 * kLinearScanThreshold) {
};
}} // namespaces
-
-#endif // FOLLY_EXPERIMENTAL_ELIAS_FANO_CODING_H
projects / folly.git / blobdiff