GH-45819: [C++] Add OptionalBitmapAnd utility

cpp/src/arrow/util/bitmap_ops.cc

@@ -329,6 +329,25 @@ bool OptionalBitmapEquals(const std::shared_ptr<Buffer>& left, int64_t left_offs
                               right ? right->data() : nullptr, right_offset, length);
 }
 
+Result<std::shared_ptr<Buffer>> OptionalBitmapAnd(MemoryPool* pool,
+                                                  const std::shared_ptr<Buffer>& left,
+                                                  int64_t left_offset,
+                                                  const std::shared_ptr<Buffer>& right,
+                                                  int64_t right_offset, int64_t length,
+                                                  int64_t out_offset) {
+  if (left == nullptr && right == nullptr) {
+    return nullptr;
+  }
+  if (left == nullptr) {
+    return CopyBitmap(pool, right->data(), right_offset, length, out_offset);
+  }
+  if (right == nullptr) {
+    return CopyBitmap(pool, left->data(), left_offset, length, out_offset);
+  }
+  return BitmapAnd(pool, left->data(), left_offset, right->data(), right_offset, length,
+                   out_offset);
+}
+
 namespace {
 
 template <template <typename> class BitOp>

cpp/src/arrow/util/bitmap_ops.h

@@ -166,6 +166,29 @@ ARROW_EXPORT
 void BitmapAnd(const uint8_t* left, int64_t left_offset, const uint8_t* right,
                int64_t right_offset, int64_t length, int64_t out_offset, uint8_t* out);
 
+/// \brief Do a "bitmap and" on two buffers, handling null buffers safely.
+///
+/// If both buffers are null, returns nullptr.
+/// If one buffer is null, allocates a new buffer and copies the valid buffer into it.
+/// If both buffers are valid, allocates a new buffer and performs a bitwise AND.
+///
+/// \param[in] pool memory pool to allocate memory from
+/// \param[in] left left source buffer (may be null)
+/// \param[in] left_offset bit offset into the left buffer
+/// \param[in] right right source buffer (may be null)
+/// \param[in] right_offset bit offset into the right buffer
+/// \param[in] length number of bits to compute
+/// \param[in] out_offset bit offset into the output buffer
+///
+/// \return Resulting buffer (may be null)
+ARROW_EXPORT
+Result<std::shared_ptr<Buffer>> OptionalBitmapAnd(MemoryPool* pool,
+                                                  const std::shared_ptr<Buffer>& left,
+                                                  int64_t left_offset,
+                                                  const std::shared_ptr<Buffer>& right,
+                                                  int64_t right_offset, int64_t length,
+                                                  int64_t out_offset);
+
 /// \brief Do a "bitmap or" for the given bit length on right and left buffers
 /// starting at their respective bit-offsets and put the results in out_buffer
 /// starting at the given bit-offset.

cpp/src/arrow/util/bitmap_test.cc

@@ -17,6 +17,7 @@
 
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
+#include <cstring>
 
 #include "arrow/array/array_base.h"
 #include "arrow/array/data.h"
@@ -1236,6 +1237,45 @@ TEST(BitmapOpTest, PartialLeadingByteSafety) {
   }
 }
 
+TEST(BitmapOpTest, OptionalBitmapAnd) {
+  MemoryPool* pool = default_memory_pool();
+  int64_t length = 16;
+  int64_t phys_bits = length;
+
+  // Create two distinct test buffers
+  ASSERT_OK_AND_ASSIGN(auto buf1, AllocateEmptyBitmap(phys_bits, pool));
+  ASSERT_OK_AND_ASSIGN(auto buf2, AllocateEmptyBitmap(phys_bits, pool));
+
+  // Fill buf1 with 1s (true)
+  std::memset(buf1->mutable_data(), 0xFF, buf1->size());
+  // Fill buf2 with alternating bits 01010101 (0xAA)
+  std::memset(buf2->mutable_data(), 0xAA, buf2->size());
+
+  // State 1: Both nullptr
+  ASSERT_OK_AND_ASSIGN(auto result1,
+                       OptionalBitmapAnd(pool, nullptr, 0, nullptr, 0, length, 0));
+  ASSERT_EQ(result1, nullptr);
+
+  // State 2: Left nullptr, Right valid (Should copy Right)
+  ASSERT_OK_AND_ASSIGN(auto result2,
+                       OptionalBitmapAnd(pool, nullptr, 0, buf2, 0, length, 0));
+  ASSERT_NE(result2, nullptr);
+  EXPECT_TRUE(BitmapEquals(buf2->data(), 0, result2->data(), 0, length));
+
+  // State 3: Left valid, Right nullptr (Should copy Left)
+  ASSERT_OK_AND_ASSIGN(auto result3,
+                       OptionalBitmapAnd(pool, buf1, 0, nullptr, 0, length, 0));
+  ASSERT_NE(result3, nullptr);
+  EXPECT_TRUE(BitmapEquals(buf1->data(), 0, result3->data(), 0, length));
+
+  // State 4: Both valid (Should perform Bitwise AND)
+  ASSERT_OK_AND_ASSIGN(auto result4,
+                       OptionalBitmapAnd(pool, buf1, 0, buf2, 0, length, 0));
+  ASSERT_NE(result4, nullptr);
+  // Since buf1 is all 1s, (buf1 AND buf2) should perfectly equal buf2
+  EXPECT_TRUE(BitmapEquals(buf2->data(), 0, result4->data(), 0, length));
+}
+
 // Tests for Bitmap visiting.
 
 // test the basic assumption of word level Bitmap::Visit