From 8b620bb5ef8a867ca802e424b3ab8c87bcacc41d Mon Sep 17 00:00:00 2001
From: Vishwanatha-HD <Vishwanatha.HD@ibm.com>
Date: Fri, 21 Nov 2025 22:50:44 +0530
Subject: [PATCH] GH-48214 Fix Arrow Reader Internal logic to enable Parquet DB
 support on s390x

---
 cpp/src/parquet/arrow/reader_internal.cc | 34 ++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/cpp/src/parquet/arrow/reader_internal.cc b/cpp/src/parquet/arrow/reader_internal.cc
index 12f36fe39cf..c33a200be35 100644
--- a/cpp/src/parquet/arrow/reader_internal.cc
+++ b/cpp/src/parquet/arrow/reader_internal.cc
@@ -851,7 +851,41 @@ Status TransferHalfFloat(RecordReader* reader, MemoryPool* pool,
   std::shared_ptr<ChunkedArray> chunked_array;
   RETURN_NOT_OK(
       TransferBinary(reader, pool, field->WithType(binary_type), &chunked_array));
+#if ARROW_LITTLE_ENDIAN
   ARROW_ASSIGN_OR_RAISE(*out, chunked_array->View(field->type()));
+#else
+  // Convert little-endian bytes from Parquet to native-endian HalfFloat
+  std::vector<std::shared_ptr<::arrow::Array>> out_chunks;
+  out_chunks.reserve(chunked_array->num_chunks());
+
+  for (const auto& chunk : chunked_array->chunks()) {
+    auto fsb = std::static_pointer_cast<::arrow::FixedSizeBinaryArray>(chunk);
+    const int64_t n = fsb->length();
+
+    // Allocate buffer for native-endian uint16 values
+    ARROW_ASSIGN_OR_RAISE(auto data_buf,
+                          ::arrow::AllocateBuffer(n * sizeof(uint16_t), pool));
+    auto* out16 = reinterpret_cast<uint16_t*>(data_buf->mutable_data());
+
+    // Copy and convert from little-endian (Parquet spec) to native-endian
+    for (int64_t i = 0; i < n; ++i) {
+      uint16_t v;
+      std::memcpy(&v, fsb->GetValue(i), sizeof(uint16_t));
+      // Parquet spec: float16 stored as little-endian; convert to native
+      out16[i] = ::arrow::bit_util::FromLittleEndian(v);
+    }
+
+    // Create HalfFloatArray with the converted data
+    auto arr_data = ::arrow::ArrayData::Make(::arrow::float16(), n,
+                                             {fsb->null_bitmap(), std::move(data_buf)},
+                                             fsb->null_count());
+
+    out_chunks.push_back(::arrow::MakeArray(std::move(arr_data)));
+  }
+
+  *out =
+      std::make_shared<::arrow::ChunkedArray>(std::move(out_chunks), ::arrow::float16());
+#endif
   return Status::OK();
 }