From 320cbfc818984b69b6f35039db53f6ad7a8ac47a Mon Sep 17 00:00:00 2001
From: Gang Wu <ustcwg@gmail.com>
Date: Wed, 2 Sep 2026 14:40:02 +0800
Subject: [PATCH] GH-51135: [C++][Parquet] Avoid misaligned stores when reading
 BYTE_ARRAY decimals

---
 cpp/src/parquet/arrow/reader_internal.cc | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/cpp/src/parquet/arrow/reader_internal.cc b/cpp/src/parquet/arrow/reader_internal.cc
index 12f36fe39cf8..b5207aca253f 100644
--- a/cpp/src/parquet/arrow/reader_internal.cc
+++ b/cpp/src/parquet/arrow/reader_internal.cc
@@ -725,9 +725,7 @@ struct DecimalConverter<DecimalArrayType, ByteArrayType> {
         return Status::Invalid("Invalid BYTE_ARRAY length for ", type->ToString());
       }
 
-      auto out_ptr_view = reinterpret_cast<uint64_t*>(out_ptr);
-      out_ptr_view[0] = 0;
-      out_ptr_view[1] = 0;
+      std::memset(out_ptr, 0, type_length);
 
       // only convert rows that are not null if there are nulls, or
       // all rows, if there are not