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.venv/Lib/site-packages/pyarrow/include/arrow/util/bitmap_visit.h

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+// 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.
+
+#pragma once
+
+#include <cstdint>
+
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_reader.h"
+
+namespace arrow {
+namespace internal {
+
+// A function that visits each bit in a bitmap and calls a visitor function with a
+// boolean representation of that bit. This is intended to be analogous to
+// GenerateBits.
+template <class Visitor>
+void VisitBits(const uint8_t* bitmap, int64_t start_offset, int64_t length,
+               Visitor&& visit) {
+  BitmapReader reader(bitmap, start_offset, length);
+  for (int64_t index = 0; index < length; ++index) {
+    visit(reader.IsSet());
+    reader.Next();
+  }
+}
+
+// Like VisitBits(), but unrolls its main loop for better performance.
+template <class Visitor>
+void VisitBitsUnrolled(const uint8_t* bitmap, int64_t start_offset, int64_t length,
+                       Visitor&& visit) {
+  if (length == 0) {
+    return;
+  }
+
+  // Start by visiting any bits preceding the first full byte.
+  int64_t num_bits_before_full_bytes =
+      bit_util::RoundUpToMultipleOf8(start_offset) - start_offset;
+  // Truncate num_bits_before_full_bytes if it is greater than length.
+  if (num_bits_before_full_bytes > length) {
+    num_bits_before_full_bytes = length;
+  }
+  // Use the non loop-unrolled VisitBits since we don't want to add branches
+  VisitBits<Visitor>(bitmap, start_offset, num_bits_before_full_bytes, visit);
+
+  // Shift the start pointer to the first full byte and compute the
+  // number of full bytes to be read.
+  const uint8_t* first_full_byte = bitmap + bit_util::CeilDiv(start_offset, 8);
+  const int64_t num_full_bytes = (length - num_bits_before_full_bytes) / 8;
+
+  // Iterate over each full byte of the input bitmap and call the visitor in
+  // a loop-unrolled manner.
+  for (int64_t byte_index = 0; byte_index < num_full_bytes; ++byte_index) {
+    // Get the current bit-packed byte value from the bitmap.
+    const uint8_t byte = *(first_full_byte + byte_index);
+
+    // Execute the visitor function on each bit of the current byte.
+    visit(bit_util::GetBitFromByte(byte, 0));
+    visit(bit_util::GetBitFromByte(byte, 1));
+    visit(bit_util::GetBitFromByte(byte, 2));
+    visit(bit_util::GetBitFromByte(byte, 3));
+    visit(bit_util::GetBitFromByte(byte, 4));
+    visit(bit_util::GetBitFromByte(byte, 5));
+    visit(bit_util::GetBitFromByte(byte, 6));
+    visit(bit_util::GetBitFromByte(byte, 7));
+  }
+
+  // Write any leftover bits in the last byte.
+  const int64_t num_bits_after_full_bytes = (length - num_bits_before_full_bytes) % 8;
+  VisitBits<Visitor>(first_full_byte + num_full_bytes, 0, num_bits_after_full_bytes,
+                     visit);
+}
+
+}  // namespace internal
+}  // namespace arrow