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SERVER-82971 Implement optimized block-based simple8b sum 

This is significantly faster than the previous implementation.
The block-based sum will be used to efficiently calculate the delta for the last element in a BSONColumn.
This commit is contained in:
Henrik Edin 2023-11-30 18:17:58 +00:00 committed by Evergreen Agent
parent dd52961205
commit 20d0dd80d4
7 changed files with 674 additions and 4 deletions
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1
src/mongo/bson/util/SConscript
View File

@ -19,6 +19,7 @@ env.Library(
source=[ source=[
'bsoncolumn.cpp', 'bsoncolumn.cpp',
'bsoncolumnbuilder.cpp', 'bsoncolumnbuilder.cpp',
'simple8b.cpp',
'simple8b_builder.cpp', 'simple8b_builder.cpp',
'simple8b_type_util.cpp', 'simple8b_type_util.cpp',
], ],

530
src/mongo/bson/util/simple8b.cpp Normal file
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@ -0,0 +1,530 @@
/**
* Copyright (C) 2023-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/bson/util/simple8b.h"
#include "mongo/bson/util/simple8b_type_util.h"
#include <limits>
namespace mongo::simple8b {
namespace {
// Performs addition as unsigned and cast back to signed to get overflow defined to wrapped around
// instead of undefined behavior.
static constexpr int64_t add(int64_t lhs, int64_t rhs) {
return static_cast<int64_t>(static_cast<uint64_t>(lhs) + static_cast<uint64_t>(rhs));
}
static constexpr int128_t add(int128_t lhs, int128_t rhs) {
return static_cast<int128_t>(static_cast<uint128_t>(lhs) + static_cast<uint128_t>(rhs));
}
// Simple Simple8b decoder for decoding any basic simple8b block where all bits are used for the
// value, decodes signed integer at runtime. Suitable for selectors with many bits per slot. Encoded
// should be be machine endian and first slot should start at least significant bit.
template <int bits>
struct SimpleDecoder {
// Number of values in this block.
static constexpr int iters = 60 / bits;
// Bit mask to extract a single slot and to check for the missing bit pattern.
static constexpr uint64_t mask = (1ull << bits) - 1;
// Calculate the sum of all slots.
template <typename T>
static T sum(uint64_t encoded) {
T decoded = 0;
for (int i = iters; i; --i) {
uint64_t slot = encoded & mask;
if (slot != mask) {
decoded = add(decoded, Simple8bTypeUtil::decodeInt64(slot));
}
encoded >>= bits;
};
return decoded;
}
// Returns value of last slot. Treats missing as 0.
static int64_t lastIgnoreSkip(uint64_t encoded) {
encoded >>= (bits * (iters - 1));
if (encoded == mask)
return 0;
return Simple8bTypeUtil::decodeInt64(encoded);
}
};
// Table-based decoder that uses a lookup table for decoding unsigned integers into signed. Suitable
// for selectors with few bits per slot as the internal lookup table grows with bits per slot.
// Encoded should be be machine endian and first slot should start at least significant bit.
template <int bits>
struct TableDecoder {
// Type to store in lookup table, depends on bit width per slot.
using T = std::conditional_t<bits <= 8, int8_t, int16_t>;
// Constant to constrain table size.
static constexpr int kMaxTableSize = 1 << 13;
static constexpr int shift = bits;
// Number of values in this block
static constexpr int iters = (60 / bits * bits + shift - 1) / shift;
// Number of entries in lookup table
static constexpr int entries = 1 << shift;
// Bit mask to extract a single slot and to check for the missing bit pattern.
static constexpr uint64_t mask = (1ull << bits) - 1;
// Largest possible value that can be stored in this slot
static constexpr int64_t kMaxSlotValue = Simple8bTypeUtil::decodeInt64(mask - 1);
// Smallest possible value that can be stored in this slot
static constexpr int64_t kMinSlotValue = Simple8bTypeUtil::decodeInt64(mask - 2);
// Verify that lookup table is within size limit and that it can store our possible range of
// values
static_assert(entries <= kMaxTableSize, "lookup table too large");
static_assert(kMaxSlotValue <= std::numeric_limits<T>::max(),
"lookup table cannot store full decoded value range");
static_assert(kMinSlotValue >= std::numeric_limits<T>::min(),
"lookup table cannot store full decoded value range");
T table[entries];
// Initialize lookup table
constexpr TableDecoder() : table() {
for (unsigned i = 0; i < entries; ++i) {
uint64_t slot = i;
bool skip = slot == mask;
if (!skip) {
table[i] += Simple8bTypeUtil::decodeInt64(slot);
}
}
}
// Calculate the sum of all slots
template <typename T>
T sum(uint64_t encoded) const {
T decoded = 0;
for (int i = iters; i; --i) {
decoded += table[encoded % entries];
encoded >>= shift;
};
return decoded;
}
// Returns value of last slot. Treats missing as 0
int64_t lastIgnoreSkip(uint64_t encoded) const {
encoded >>= (bits * (iters - 1));
return table[encoded];
}
};
// Table-based decoder that uses a lookup table for decoding multiple unsigned integers into signed
// at once. Suitable for selectors with few bits per slot as the internal lookup table grows with
// bits per slot. Encoded should be be machine endian and first slot should start at least
// significant bit.
template <int bits>
struct ParallelTableDecoder {
// Constant to constrain table size, 2^X.
static constexpr int kMaxTableSizeExp = 13;
static constexpr int kMaxTableSize = 1 << kMaxTableSizeExp;
// Number of slots that we can decode together
static constexpr int parallel = kMaxTableSizeExp / bits;
// Number of shift to get to the next decoding iteration.
static constexpr int shift = bits * parallel;
// Number of decoding iterations in this block
static constexpr int iters = (60 / bits * bits + shift - 1) / shift;
// Number of entries in lookup table
static constexpr int entries = 1 << shift;
// Bit mask to extract a single slot and to check for the missing bit pattern.
static constexpr uint64_t mask = (1ull << bits) - 1;
// Largest possible value that can be stored in this slot
static constexpr int64_t kMaxSlotValue = Simple8bTypeUtil::decodeInt64(mask - 1);
// Smallest possible value that can be stored in this slot
static constexpr int64_t kMinSlotValue = Simple8bTypeUtil::decodeInt64(mask - 2);
// Verify that lookup table is within size limit and that it can store our possible range of
// values
static_assert(
bits > 1,
"simple8b slots needs to use at least 2 bits to be meaningful for parallel decoding");
static_assert(parallel > 1, "bit size too large to fit in table for parallel decoding");
static_assert(kMaxSlotValue * parallel <= std::numeric_limits<int8_t>::max(),
"lookup table cannot store full decoded value range");
static_assert(kMinSlotValue * parallel >= std::numeric_limits<int8_t>::min(),
"lookup table cannot store full decoded value range");
int8_t table[entries];
// Initialize lookup table
constexpr ParallelTableDecoder() : table() {
for (unsigned i = 0; i < entries; ++i) {
for (int j = 0; j < parallel; ++j) {
uint64_t slot = (i >> (j * bits)) & mask;
if (slot != mask) {
table[i] += Simple8bTypeUtil::decodeInt64(slot);
}
}
}
}
// Calculate the sum of all slots
template <typename T>
T sum(uint64_t encoded) const {
T decoded = 0;
for (int i = iters; i; --i) {
decoded = add(decoded, table[encoded % entries]);
encoded >>= shift;
};
return decoded;
}
};
// Special Simple8b decoder for decoding the extended selectors where the slot bits are split up in
// a value and count for a left shift. Encoded should be be machine endian and first slot should
// start at least significant bit.
template <int valueBits, int countBits, int countScale>
struct ExtendedDecoder {
static constexpr int bits = valueBits + countBits;
static constexpr int iters = 56 / bits;
static constexpr uint64_t mask = (1ull << bits) - 1;
static constexpr uint64_t valueMask = (1ull << valueBits) - 1;
static constexpr uint64_t countMask = (1ull << countBits) - 1;
// Calculate the sum of all slots
template <typename T>
T sum(uint64_t encoded) const {
T decoded = 0;
for (int i = iters; i; --i) {
if ((encoded & mask) != mask) {
uint64_t count = encoded & countMask;
make_unsigned_t<T> value = (encoded >> countBits) & valueMask;
decoded = add(decoded, Simple8bTypeUtil::decodeInt(value << (count * countScale)));
}
encoded >>= bits;
};
return decoded;
}
// Returns value of last slot. Treats missing as 0
template <typename T>
T lastIgnoreSkip(uint64_t encoded) const {
encoded >>= (bits * (iters - 1));
if ((encoded & mask) == mask)
return 0;
uint64_t count = encoded & countMask;
make_unsigned_t<T> value = (encoded >> countBits) & valueMask;
return Simple8bTypeUtil::decodeInt(value << (count * countScale));
}
};
// Storage for all decoders that we need for our various selector types
static constexpr ParallelTableDecoder<2> decoderParallel2;
static constexpr ParallelTableDecoder<3> decoderParallel3;
static constexpr ParallelTableDecoder<4> decoderParallel4;
static constexpr ParallelTableDecoder<5> decoderParallel5;
static constexpr ParallelTableDecoder<6> decoderParallel6;
static constexpr TableDecoder<2> decoder2;
static constexpr TableDecoder<3> decoder3;
static constexpr TableDecoder<4> decoder4;
static constexpr TableDecoder<5> decoder5;
static constexpr TableDecoder<6> decoder6;
static constexpr TableDecoder<7> decoder7;
static constexpr TableDecoder<8> decoder8;
static constexpr TableDecoder<10> decoder10;
static constexpr TableDecoder<12> decoder12;
static constexpr SimpleDecoder<15> decoder15;
static constexpr SimpleDecoder<20> decoder20;
static constexpr SimpleDecoder<30> decoder30;
static constexpr SimpleDecoder<60> decoder60;
static constexpr ExtendedDecoder<2, 4, 1> decoderExtended7_1;
static constexpr ExtendedDecoder<3, 4, 1> decoderExtended7_2;
static constexpr ExtendedDecoder<4, 4, 1> decoderExtended7_3;
static constexpr ExtendedDecoder<5, 4, 1> decoderExtended7_4;
static constexpr ExtendedDecoder<7, 4, 1> decoderExtended7_5;
static constexpr ExtendedDecoder<10, 4, 1> decoderExtended7_6;
static constexpr ExtendedDecoder<14, 4, 1> decoderExtended7_7;
static constexpr ExtendedDecoder<24, 4, 1> decoderExtended7_8;
static constexpr ExtendedDecoder<52, 4, 1> decoderExtended7_9;
static constexpr ExtendedDecoder<4, 4, 4> decoderExtended8_1;
static constexpr ExtendedDecoder<5, 4, 4> decoderExtended8_2;
static constexpr ExtendedDecoder<7, 4, 4> decoderExtended8_3;
static constexpr ExtendedDecoder<10, 4, 4> decoderExtended8_4;
static constexpr ExtendedDecoder<14, 4, 4> decoderExtended8_5;
static constexpr ExtendedDecoder<24, 4, 4> decoderExtended8_6;
static constexpr ExtendedDecoder<52, 4, 4> decoderExtended8_7;
static constexpr ExtendedDecoder<4, 5, 4> decoderExtended8_8;
static constexpr ExtendedDecoder<6, 5, 4> decoderExtended8_9;
static constexpr ExtendedDecoder<9, 5, 4> decoderExtended8_10;
static constexpr ExtendedDecoder<13, 5, 4> decoderExtended8_11;
static constexpr ExtendedDecoder<23, 5, 4> decoderExtended8_12;
static constexpr ExtendedDecoder<51, 5, 4> decoderExtended8_13;
// Decodes last slot for simple8b block. Treats missing as 0.
template <typename T>
T decodeLastSlotIgnoreSkip(uint64_t encoded) {
auto selector = encoded & simple8b_internal::kBaseSelectorMask;
encoded >>= 4;
switch (selector) {
case 1: // Only 0 or missing deltas
break;
case 2:
return decoder2.lastIgnoreSkip(encoded);
case 3:
return decoder3.lastIgnoreSkip(encoded);
case 4:
return decoder4.lastIgnoreSkip(encoded);
case 5:
return decoder5.lastIgnoreSkip(encoded);
case 6:
return decoder6.lastIgnoreSkip(encoded);
case 7: {
auto extended = encoded & simple8b_internal::kBaseSelectorMask;
encoded >>= 4;
switch (extended) {
case 0:
return decoder7.lastIgnoreSkip(encoded);
case 1:
return decoderExtended7_1.lastIgnoreSkip<T>(encoded);
case 2:
return decoderExtended7_2.lastIgnoreSkip<T>(encoded);
case 3:
return decoderExtended7_3.lastIgnoreSkip<T>(encoded);
case 4:
return decoderExtended7_4.lastIgnoreSkip<T>(encoded);
case 5:
return decoderExtended7_5.lastIgnoreSkip<T>(encoded);
case 6:
return decoderExtended7_6.lastIgnoreSkip<T>(encoded);
case 7:
return decoderExtended7_7.lastIgnoreSkip<T>(encoded);
case 8:
return decoderExtended7_8.lastIgnoreSkip<T>(encoded);
case 9:
return decoderExtended7_9.lastIgnoreSkip<T>(encoded);
default:
invariant(false); // invalid encoding
break;
}
break;
}
case 8: {
auto extended = encoded & simple8b_internal::kBaseSelectorMask;
encoded >>= 4;
switch (extended) {
case 0:
return decoder8.lastIgnoreSkip(encoded);
case 1:
return decoderExtended8_1.lastIgnoreSkip<T>(encoded);
case 2:
return decoderExtended8_2.lastIgnoreSkip<T>(encoded);
case 3:
return decoderExtended8_3.lastIgnoreSkip<T>(encoded);
case 4:
return decoderExtended8_4.lastIgnoreSkip<T>(encoded);
case 5:
return decoderExtended8_5.lastIgnoreSkip<T>(encoded);
case 6:
return decoderExtended8_6.lastIgnoreSkip<T>(encoded);
case 7:
return decoderExtended8_7.lastIgnoreSkip<T>(encoded);
case 8:
return decoderExtended8_8.lastIgnoreSkip<T>(encoded);
case 9:
return decoderExtended8_9.lastIgnoreSkip<T>(encoded);
case 10:
return decoderExtended8_10.lastIgnoreSkip<T>(encoded);
case 11:
return decoderExtended8_11.lastIgnoreSkip<T>(encoded);
case 12:
return decoderExtended8_12.lastIgnoreSkip<T>(encoded);
case 13:
return decoderExtended8_13.lastIgnoreSkip<T>(encoded);
default:
invariant(false); // invalid encoding
break;
}
break;
}
case 9:
return decoder10.lastIgnoreSkip(encoded);
case 10:
return decoder12.lastIgnoreSkip(encoded);
case 11:
return decoder15.lastIgnoreSkip(encoded);
case 12:
return decoder20.lastIgnoreSkip(encoded);
case 13:
return decoder30.lastIgnoreSkip(encoded);
case 14:
return decoder60.lastIgnoreSkip(encoded);
case 15:
break;
default:
break;
}
return 0;
}
// Decodes and sums all slots in simple8b block, writes last encountered non-rle block in
// 'prevNonRLE'.
template <typename T>
T decodeAndSum(uint64_t encoded, uint64_t* prevNonRLE) {
auto selector = encoded & simple8b_internal::kBaseSelectorMask;
if (selector != simple8b_internal::kRleSelector) {
*prevNonRLE = encoded;
}
encoded >>= 4;
switch (selector) {
case 1: // Only 0 or missing deltas
return 0;
case 2:
return decoderParallel2.sum<T>(encoded);
case 3:
return decoderParallel3.sum<T>(encoded);
case 4:
return decoderParallel4.sum<T>(encoded);
case 5:
return decoderParallel5.sum<T>(encoded);
case 6:
return decoderParallel6.sum<T>(encoded);
case 7: {
auto extended = encoded & simple8b_internal::kBaseSelectorMask;
encoded >>= 4;
switch (extended) {
case 0:
return decoder7.sum<T>(encoded);
case 1:
return decoderExtended7_1.sum<T>(encoded);
case 2:
return decoderExtended7_2.sum<T>(encoded);
case 3:
return decoderExtended7_3.sum<T>(encoded);
case 4:
return decoderExtended7_4.sum<T>(encoded);
case 5:
return decoderExtended7_5.sum<T>(encoded);
case 6:
return decoderExtended7_6.sum<T>(encoded);
case 7:
return decoderExtended7_7.sum<T>(encoded);
case 8:
return decoderExtended7_8.sum<T>(encoded);
case 9:
return decoderExtended7_9.sum<T>(encoded);
default:
break;
}
break;
}
case 8: {
auto extended = encoded & simple8b_internal::kBaseSelectorMask;
encoded >>= 4;
switch (extended) {
case 0:
return decoder8.sum<T>(encoded);
case 1:
return decoderExtended8_1.sum<T>(encoded);
case 2:
return decoderExtended8_2.sum<T>(encoded);
case 3:
return decoderExtended8_3.sum<T>(encoded);
case 4:
return decoderExtended8_4.sum<T>(encoded);
case 5:
return decoderExtended8_5.sum<T>(encoded);
case 6:
return decoderExtended8_6.sum<T>(encoded);
case 7:
return decoderExtended8_7.sum<T>(encoded);
case 8:
return decoderExtended8_8.sum<T>(encoded);
case 9:
return decoderExtended8_9.sum<T>(encoded);
case 10:
return decoderExtended8_10.sum<T>(encoded);
case 11:
return decoderExtended8_11.sum<T>(encoded);
case 12:
return decoderExtended8_12.sum<T>(encoded);
case 13:
return decoderExtended8_13.sum<T>(encoded);
default:
break;
}
break;
}
case 9:
return decoder10.sum<T>(encoded);
case 10:
return decoder12.sum<T>(encoded);
case 11:
return decoder15.sum<T>(encoded);
case 12:
return decoder20.sum<T>(encoded);
case 13:
return decoder30.sum<T>(encoded);
case 14:
return decoder60.sum<T>(encoded);
case simple8b_internal::kRleSelector:
return decodeLastSlotIgnoreSkip<T>(*prevNonRLE) * ((encoded & 0xf) + 1) *
simple8b_internal::kRleMultiplier;
default:
break;
}
fassertFailed(8297100);
return 0;
}
} // namespace
template <typename T>
T sum(const char* buffer, size_t size, uint64_t& prevNonRLE) {
invariant(size % 8 == 0);
const char* end = buffer + size;
T sum = 0;
while (buffer != end) {
uint64_t encoded = ConstDataView(buffer).read<LittleEndian<uint64_t>>();
sum = add(sum, decodeAndSum<T>(encoded, &prevNonRLE));
buffer += sizeof(uint64_t);
}
return sum;
}
// Explicit template instantiations for our supported types
template int64_t sum<int64_t>(const char*, size_t, uint64_t&);
template int128_t sum<int128_t>(const char*, size_t, uint64_t&);
} // namespace mongo::simple8b

13
src/mongo/bson/util/simple8b.h
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@ -334,4 +334,17 @@ typename Simple8b<T>::Iterator Simple8b<T>::end() const {
return {_buffer + _size}; return {_buffer + _size};
} }
namespace simple8b {
// Constant for a simple8b block containing a single 'missing' value.
static constexpr uint64_t kSingleSkip = 0xFFFFFFFFFFFFFFFE;
/**
* Calculates the sum for multiple simple8b blocks in a buffer. 'prevNonRLE' should be initialized
* to 'kSingleSkip' when calculating sum for the first buffer. If the caller needs sum from multiple
* buffers the value should be passed along between the calls.
*/
template <typename T>
T sum(const char* buffer, size_t size, uint64_t& prevNonRLE);
} // namespace simple8b
} // namespace mongo } // namespace mongo

67
src/mongo/bson/util/simple8b_bm.cpp
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@ -31,16 +31,42 @@
#include <cstddef> #include <cstddef>
#include <cstdint> #include <cstdint>
#include <iterator> #include <iterator>
#include <random>
#include <boost/cstdint.hpp> #include <boost/cstdint.hpp>
#include "mongo/bson/util/builder.h" #include "mongo/bson/util/builder.h"
#include "mongo/bson/util/simple8b.h" #include "mongo/bson/util/simple8b.h"
#include "mongo/bson/util/simple8b_builder.h" #include "mongo/bson/util/simple8b_builder.h"
#include "mongo/bson/util/simple8b_type_util.h"
#include "mongo/util/shared_buffer.h" #include "mongo/util/shared_buffer.h"
namespace mongo { namespace mongo {
BufBuilder generateIntegers() {
std::mt19937_64 seedGen(1337);
std::mt19937 gen(seedGen());
std::normal_distribution<> d(100, 10);
std::uniform_int_distribution skip(1, 100);
BufBuilder buffer;
Simple8bBuilder<uint64_t> s8bBuilder(
[&buffer](uint64_t simple8bBlock) { buffer.appendNum(simple8bBlock); });
// Generate 10k integers
for (int i = 0; i < 10000; ++i) {
// 5% chance for missing
if (skip(gen) <= 5) {
s8bBuilder.skip();
} else {
s8bBuilder.append(std::lround(d(gen)));
}
}
s8bBuilder.flush();
return buffer;
}
void BM_increasingValues(benchmark::State& state) { void BM_increasingValues(benchmark::State& state) {
size_t totalBytes = 0; size_t totalBytes = 0;
for (auto _ : state) { for (auto _ : state) {
@ -152,11 +178,52 @@ void BM_decode(benchmark::State& state) {
state.SetBytesProcessed(totalBytes); state.SetBytesProcessed(totalBytes);
} }
void BM_sum(benchmark::State& state) {
BufBuilder buffer = generateIntegers();
auto size = buffer.len();
auto buf = buffer.release();
size_t totalBytes = 0;
for (auto _ : state) {
benchmark::ClobberMemory();
uint64_t prev = simple8b::kSingleSkip;
benchmark::DoNotOptimize(simple8b::sum<int64_t>(buf.get(), size, prev));
totalBytes += size;
}
state.SetBytesProcessed(totalBytes);
}
void BM_sumUnoptimized(benchmark::State& state) {
BufBuilder buffer = generateIntegers();
auto size = buffer.len();
auto buf = buffer.release();
size_t totalBytes = 0;
for (auto _ : state) {
benchmark::ClobberMemory();
Simple8b<uint64_t> s8b(buf.get(), size);
int64_t sum = 0;
for (auto&& val : s8b) {
if (val) {
sum += Simple8bTypeUtil::decodeInt64(*val);
}
}
totalBytes += size;
}
state.SetBytesProcessed(totalBytes);
}
BENCHMARK(BM_increasingValues)->Arg(100); BENCHMARK(BM_increasingValues)->Arg(100);
BENCHMARK(BM_rle)->Arg(100); BENCHMARK(BM_rle)->Arg(100);
BENCHMARK(BM_changingSmallValues)->Arg(100); BENCHMARK(BM_changingSmallValues)->Arg(100);
BENCHMARK(BM_changingLargeValues)->Arg(100); BENCHMARK(BM_changingLargeValues)->Arg(100);
BENCHMARK(BM_selectorSeven)->Arg(100); BENCHMARK(BM_selectorSeven)->Arg(100);
BENCHMARK(BM_decode); BENCHMARK(BM_decode);
BENCHMARK(BM_sum);
BENCHMARK(BM_sumUnoptimized);
} // namespace mongo } // namespace mongo

22
src/mongo/bson/util/simple8b_test.cpp
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@ -46,6 +46,7 @@
#include "mongo/base/string_data.h" #include "mongo/base/string_data.h"
#include "mongo/bson/util/builder.h" #include "mongo/bson/util/builder.h"
#include "mongo/bson/util/simple8b_builder.h" #include "mongo/bson/util/simple8b_builder.h"
#include "mongo/bson/util/simple8b_type_util.h"
#include "mongo/platform/int128.h" #include "mongo/platform/int128.h"
#include "mongo/stdx/type_traits.h" #include "mongo/stdx/type_traits.h"
#include "mongo/unittest/assert.h" #include "mongo/unittest/assert.h"
@ -54,6 +55,16 @@
using namespace mongo; using namespace mongo;
// Performs addition as unsigned and cast back to signed to get overflow defined to wrapped around
// instead of undefined behavior.
static constexpr int64_t add(int64_t lhs, int64_t rhs) {
return static_cast<int64_t>(static_cast<uint64_t>(lhs) + static_cast<uint64_t>(rhs));
}
static constexpr int128_t add(int128_t lhs, int128_t rhs) {
return static_cast<int128_t>(static_cast<uint128_t>(lhs) + static_cast<uint128_t>(rhs));
}
template <typename T> template <typename T>
void assertValuesEqual(const Simple8b<T>& actual, const std::vector<boost::optional<T>>& expected) { void assertValuesEqual(const Simple8b<T>& actual, const std::vector<boost::optional<T>>& expected) {
auto it = actual.begin(); auto it = actual.begin();
@ -104,6 +115,17 @@ void testSimple8b(const std::vector<boost::optional<T>>& expectedValues,
Simple8b<T> s8b(buffer.get(), size); Simple8b<T> s8b(buffer.get(), size);
assertValuesEqual(s8b, expectedValues); assertValuesEqual(s8b, expectedValues);
make_signed_t<T> sum = 0;
for (auto&& val : expectedValues) {
if (val) {
sum = add(sum, Simple8bTypeUtil::decodeInt(*val));
}
}
uint64_t prev = simple8b::kSingleSkip;
auto s = simple8b::sum<make_signed_t<T>>(
reinterpret_cast<const char*>(expectedBinary.data()), expectedBinary.size(), prev);
ASSERT_EQ(s, sum);
} }
template <typename T> template <typename T>

21
src/mongo/bson/util/simple8b_type_util.h
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@ -54,13 +54,13 @@ public:
// store as an unsigned integer // store as an unsigned integer
// the most significant bit position to the least significant bit and call simple8b as an // the most significant bit position to the least significant bit and call simple8b as an
// unsigned integer. // unsigned integer.
static uint64_t encodeInt64(int64_t val) { static constexpr uint64_t encodeInt64(int64_t val) {
return (static_cast<uint64_t>(val) << 1) ^ (val >> 63); return (static_cast<uint64_t>(val) << 1) ^ (val >> 63);
} }
static int64_t decodeInt64(uint64_t val) { static constexpr int64_t decodeInt64(uint64_t val) {
return (val >> 1) ^ (~(val & 1) + 1); return (val >> 1) ^ (~(val & 1) + 1);
} }
static uint128_t encodeInt128(int128_t val) { static constexpr uint128_t encodeInt128(int128_t val) {
// The Abseil right shift implementation on signed int128 is not correct as an arithmetic // The Abseil right shift implementation on signed int128 is not correct as an arithmetic
// shift in their non-intrinsic implementation. When we detect this case we replace the // shift in their non-intrinsic implementation. When we detect this case we replace the
// right arithmetic shift of 127 positions that needs to produce 0xFF..FF or 0x00..00 // right arithmetic shift of 127 positions that needs to produce 0xFF..FF or 0x00..00
@ -77,10 +77,13 @@ public:
#endif #endif
} }
static int128_t decodeInt128(uint128_t val) { static constexpr int128_t decodeInt128(uint128_t val) {
return static_cast<int128_t>((val >> 1) ^ (~(val & 1) + 1)); return static_cast<int128_t>((val >> 1) ^ (~(val & 1) + 1));
} }
template <typename T>
static constexpr auto decodeInt(T val);
// These methods are for encoding OID with simple8b. The unique identifier is not part of // These methods are for encoding OID with simple8b. The unique identifier is not part of
// the encoded integer and must thus be provided when decoding. // the encoded integer and must thus be provided when decoding.
// Re-organize the bytes so that most of the entropy is in the least significant bytes. // Re-organize the bytes so that most of the entropy is in the least significant bytes.
@ -129,4 +132,14 @@ public:
static constexpr std::array<double, kMemoryAsInteger> kScaleMultiplier = { static constexpr std::array<double, kMemoryAsInteger> kScaleMultiplier = {
1, 10, 100, 10000, 100000000}; 1, 10, 100, 10000, 100000000};
}; };
template <>
inline auto Simple8bTypeUtil::decodeInt(uint64_t val) {
return decodeInt64(val);
}
template <>
inline auto Simple8bTypeUtil::decodeInt(uint128_t val) {
return decodeInt128(val);
}
} // namespace mongo } // namespace mongo

24
src/mongo/platform/int128.h
View File

@ -33,3 +33,27 @@
using uint128_t = absl::uint128; using uint128_t = absl::uint128;
using int128_t = absl::int128; using int128_t = absl::int128;
namespace mongo {
template <typename T>
struct make_unsigned : public std::make_unsigned<T> {};
template <>
struct make_unsigned<int128_t> {
using type = uint128_t;
};
template <typename T>
struct make_signed : public std::make_signed<T> {};
template <>
struct make_signed<uint128_t> {
using type = int128_t;
};
template <typename T>
using make_unsigned_t = typename make_unsigned<T>::type;
template <typename T>
using make_signed_t = typename make_signed<T>::type;
} // namespace mongo