BitUnpacking for continuous values

Fast bit unpacking shows up to 9x improvement over Arrow BitUnpacker,
up to 30x over DuckDB, up to 10x over Lemire's FastPForLib, up to 1.6x
over Lemire's bmipacking, and 2x over the rewritten version decode1To24
in velox/dwio/common/IntDecoder.cpp. Design doc is at
#2353

velox/dwio/common/tests/BitUnpackingTest.cpp

@@ -0,0 +1,149 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed 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 "velox/dwio/common/BitUnpacking.h"
+
+#include <arrow/util/rle_encoding.h> // @manual
+#include <gtest/gtest.h>
+
+#include <random>
+
+using namespace facebook::velox;
+using namespace facebook::velox::dwio::common;
+
+template <typename T>
+class BitUnpackingTest {
+ public:
+  BitUnpackingTest() {
+    inputBuffer.resize(kNumValues * 4, 0);
+    outputBuffer.resize(kNumValues * 4, 0);
+    expectedOutputBuffer.resize(kNumValues * 4, 0);
+  }
+
+  void populateInputBuffer(
+      uint8_t bitWidth,
+      uint8_t* inputBuf,
+      uint32_t inputBytes) {
+    auto gen = std::bind(
+        std::uniform_int_distribution<uint32_t>(0, (1UL << bitWidth) - 1),
+        std::default_random_engine());
+    arrow::bit_util::BitWriter bitWriter(inputBuf, inputBytes);
+    for (auto j = 0; j < kNumValues; j++) {
+      uint32_t val = gen();
+      bitWriter.PutValue(val, bitWidth);
+    }
+    bitWriter.Flush(true);
+  }
+
+  uint32_t bytes(uint8_t bitWidth) {
+    return (kNumValues * bitWidth + 7) / 8;
+  }
+
+  void testUnpack(uint8_t bitWidth) {
+    populateInputBuffer(bitWidth, inputBuffer.data(), bytes(bitWidth));
+
+    const uint8_t* inputIter = inputBuffer.data();
+    T* outputIter = outputBuffer.data();
+    facebook::velox::dwio::common::unpack(
+        bitWidth, inputIter, bytes(bitWidth), kNumValues, outputIter);
+
+    inputIter = inputBuffer.data();
+    T* expectedOutputIter = expectedOutputBuffer.data();
+    arrow::bit_util::BitReader bitReader(inputIter, bytes(bitWidth));
+    bitReader.GetBatch(bitWidth, expectedOutputIter, kNumValues);
+
+    for (int i = 0; i < kNumValues; i++) {
+      if (outputBuffer[i] != expectedOutputBuffer[i]) {
+        break;
+      }
+      ASSERT_EQ(outputBuffer[i], expectedOutputBuffer[i]);
+    }
+  }
+  // multiple of 8
+  static const uint32_t kNumValues = 1024;
+
+  std::vector<uint8_t> inputBuffer;
+  std::vector<T> outputBuffer;
+  std::vector<T> expectedOutputBuffer;
+};
+
+TEST(BitUnpackingTest, uint8) {
+  BitUnpackingTest<uint8_t> test;
+  test.testUnpack(1);
+  test.testUnpack(2);
+  test.testUnpack(3);
+  test.testUnpack(4);
+  test.testUnpack(5);
+  test.testUnpack(6);
+  test.testUnpack(7);
+  test.testUnpack(8);
+}
+
+TEST(BitUnpackingTest, uint16) {
+  BitUnpackingTest<uint16_t> test;
+  test.testUnpack(1);
+  test.testUnpack(2);
+  test.testUnpack(3);
+  test.testUnpack(4);
+  test.testUnpack(5);
+  test.testUnpack(6);
+  test.testUnpack(7);
+  test.testUnpack(8);
+  test.testUnpack(9);
+  test.testUnpack(10);
+  test.testUnpack(11);
+  test.testUnpack(12);
+  test.testUnpack(13);
+  test.testUnpack(14);
+  test.testUnpack(15);
+  test.testUnpack(16);
+}
+
+TEST(BitUnpackingTest, uint32) {
+  BitUnpackingTest<uint32_t> test;
+  test.testUnpack(1);
+  test.testUnpack(2);
+  test.testUnpack(3);
+  test.testUnpack(4);
+  test.testUnpack(5);
+  test.testUnpack(6);
+  test.testUnpack(7);
+  test.testUnpack(8);
+  test.testUnpack(9);
+  test.testUnpack(10);
+  test.testUnpack(11);
+  test.testUnpack(12);
+  test.testUnpack(13);
+  test.testUnpack(14);
+  test.testUnpack(15);
+  test.testUnpack(16);
+  test.testUnpack(17);
+  test.testUnpack(18);
+  test.testUnpack(19);
+  test.testUnpack(20);
+  test.testUnpack(21);
+  test.testUnpack(22);
+  test.testUnpack(23);
+  test.testUnpack(24);
+  test.testUnpack(25);
+  test.testUnpack(26);
+  test.testUnpack(27);
+  test.testUnpack(28);
+  test.testUnpack(29);
+  test.testUnpack(30);
+  test.testUnpack(31);
+  test.testUnpack(32);
+}

velox/dwio/common/tests/CMakeLists.txt

@@ -65,3 +65,18 @@ target_link_libraries(
   ${ZSTD}
   ${ZLIB_LIBRARIES}
   ${TEST_LINK_LIBS})
+
+# The bit unpacking benchmark tests require arrow and duckdb
+if(VELOX_ENABLE_ARROW)
+  add_executable(velox_dwio_common_bitunpacking_test BitUnpackingTest.cpp)
+  add_test(velox_dwio_common_bitunpacking_test
+           velox_dwio_common_bitunpacking_test)
+  target_link_libraries(velox_dwio_common_bitunpacking_test arrow
+                        ${VELOX_LINK_LIBS} gtest gtest_main)
+
+  add_executable(velox_dwio_common_bitunpacking_benchmark
+                 BitUnpackingBenchmark.cpp)
+  target_link_libraries(
+    velox_dwio_common_bitunpacking_benchmark velox_dwio_common arrow duckdb
+    ${FOLLY} ${FOLLY_BENCHMARK})
+endif()