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ARROW-764: [C++] Improves performance of CopyBitmap and adds benchmarks #1422

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ARROW-764: [C++] Improves performance of CopyBitmap and adds benchmarks #1422

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6 changes: 4 additions & 2 deletions cpp/src/arrow/util/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -63,10 +63,10 @@ if (ARROW_BUILD_BENCHMARKS)
Shlwapi.lib
)
else()
target_link_libraries(arrow_benchmark_main
target_link_libraries(arrow_benchmark_main
benchmark
pthread
)
)
endif()

# TODO(wesm): Some benchmarks include gtest.h
Expand All @@ -80,4 +80,6 @@ ADD_ARROW_TEST(key-value-metadata-test)
ADD_ARROW_TEST(rle-encoding-test)
ADD_ARROW_TEST(stl-util-test)

ADD_ARROW_BENCHMARK(bit-util-benchmark)

add_subdirectory(variant)
58 changes: 58 additions & 0 deletions cpp/src/arrow/util/bit-util-benchmark.cc
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@@ -0,0 +1,58 @@
// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.

#include "benchmark/benchmark.h"

#include <vector>

#include "arrow/buffer.h"
#include "arrow/builder.h"
#include "arrow/memory_pool.h"
#include "arrow/test-util.h"
#include "arrow/util/bit-util.h"

namespace arrow {
namespace BitUtil {

static void BM_CopyBitmap(benchmark::State& state) { // NOLINT non-const reference
const int kBufferSize = state.range(0);

std::shared_ptr<Buffer> buffer;
ASSERT_OK(AllocateBuffer(default_memory_pool(), kBufferSize, &buffer));
memset(buffer->mutable_data(), 0, kBufferSize);
test::random_bytes(kBufferSize, 0, buffer->mutable_data());

const int num_bits = kBufferSize * 8;
const uint8_t* src = buffer->data();

std::shared_ptr<Buffer> copy;
while (state.KeepRunning()) {
ABORT_NOT_OK(CopyBitmap(default_memory_pool(), src, state.range(1), num_bits, &copy));
}
state.SetBytesProcessed(state.iterations() * kBufferSize * sizeof(int8_t));
}

BENCHMARK(BM_CopyBitmap)
->Args({100000, 0})
->Args({1000000, 0})
->Args({100000, 4})
->Args({1000000, 4})
->MinTime(1.0)
->Unit(benchmark::kMicrosecond);

} // namespace BitUtil
} // namespace arrow
17 changes: 9 additions & 8 deletions cpp/src/arrow/util/bit-util-test.cc
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Expand Up @@ -165,19 +165,20 @@ TEST(BitUtilTests, TestCopyBitmap) {
memset(buffer->mutable_data(), 0, kBufferSize);
test::random_bytes(kBufferSize, 0, buffer->mutable_data());

const int num_bits = kBufferSize * 8;

const uint8_t* src = buffer->data();

std::vector<int64_t> lengths = {kBufferSize * 8 - 4, kBufferSize * 8};
std::vector<int64_t> offsets = {0, 12, 16, 32, 37, 63, 64, 128};
for (int64_t offset : offsets) {
const int64_t copy_length = num_bits - offset;
for (int64_t num_bits : lengths) {
for (int64_t offset : offsets) {
const int64_t copy_length = num_bits - offset;

std::shared_ptr<Buffer> copy;
ASSERT_OK(CopyBitmap(default_memory_pool(), src, offset, copy_length, &copy));
std::shared_ptr<Buffer> copy;
ASSERT_OK(CopyBitmap(default_memory_pool(), src, offset, copy_length, &copy));

for (int64_t i = 0; i < copy_length; ++i) {
ASSERT_EQ(BitUtil::GetBit(src, i + offset), BitUtil::GetBit(copy->data(), i));
for (int64_t i = 0; i < copy_length; ++i) {
ASSERT_EQ(BitUtil::GetBit(src, i + offset), BitUtil::GetBit(copy->data(), i));
}
}
}
}
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32 changes: 30 additions & 2 deletions cpp/src/arrow/util/bit-util.cc
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Expand Up @@ -109,9 +109,37 @@ Status CopyBitmap(MemoryPool* pool, const uint8_t* data, int64_t offset, int64_t
std::shared_ptr<Buffer> buffer;
RETURN_NOT_OK(GetEmptyBitmap(pool, length, &buffer));
uint8_t* dest = buffer->mutable_data();
for (int64_t i = 0; i < length; ++i) {
BitUtil::SetBitTo(dest, i, BitUtil::GetBit(data, i + offset));

int64_t byte_offset = offset / 8;
int64_t bit_offset = offset % 8;
int64_t num_bytes = BitUtil::BytesForBits(length);
int64_t bits_to_zero = num_bytes * 8 - length;

if (bit_offset > 0) {
uint32_t carry_mask = BitUtil::kBitmask[bit_offset] - 1U;
uint32_t carry_shift = 8U - static_cast<uint32_t>(bit_offset);

uint32_t carry = 0U;
if (BitUtil::BytesForBits(length + bit_offset) > num_bytes) {
carry = (data[byte_offset + num_bytes] & carry_mask) << carry_shift;
}

int64_t i = num_bytes - 1;
while (i + 1 > 0) {
uint8_t cur_byte = data[byte_offset + i];
dest[i] = static_cast<uint8_t>((cur_byte >> bit_offset) | carry);
carry = (cur_byte & carry_mask) << carry_shift;
--i;
}
} else {
std::memcpy(dest, data + byte_offset, static_cast<size_t>(num_bytes));
}

for (int64_t i = length; i < length + bits_to_zero; ++i) {
// Both branches may copy extra bits - unsetting to match specification.
BitUtil::SetBitTo(dest, i, false);
}

*out = buffer;
return Status::OK();
}
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9 changes: 3 additions & 6 deletions cpp/src/arrow/util/bit-util.h
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Expand Up @@ -139,13 +139,10 @@ static inline void SetArrayBit(uint8_t* bits, int i, bool is_set) {
}

static inline void SetBitTo(uint8_t* bits, int64_t i, bool bit_is_set) {
// TODO: speed up. See https://graphics.stanford.edu/~seander/bithacks.html
// https://graphics.stanford.edu/~seander/bithacks.html
// "Conditionally set or clear bits without branching"
if (bit_is_set) {
SetBit(bits, i);
} else {
ClearBit(bits, i);
}
bits[i / 8] ^= static_cast<uint8_t>(-static_cast<uint8_t>(bit_is_set) ^ bits[i / 8]) &
kBitmask[i % 8];
}

// Returns the minimum number of bits needed to represent the value of 'x'
Expand Down