GH-48206 Fix Statistics logic to enable Parquet DB support on s390x

Author: Vishwanatha-HD

cpp/src/parquet/statistics.cc

@@ -30,6 +30,7 @@
 #include "arrow/type_traits.h"
 #include "arrow/util/bit_run_reader.h"
 #include "arrow/util/checked_cast.h"
+#include "arrow/util/endian.h"
 #include "arrow/util/float16.h"
 #include "arrow/util/logging_internal.h"
 #include "arrow/util/ubsan.h"
@@ -925,6 +926,38 @@ void TypedStatisticsImpl<DType>::UpdateSpaced(const T* values, const uint8_t* va
 
 template <typename DType>
 void TypedStatisticsImpl<DType>::PlainEncode(const T& src, std::string* dst) const {
+#if !ARROW_LITTLE_ENDIAN
+  // For fixed-width numeric types, write explicit little-endian bytes per spec
+  if constexpr (std::is_same_v<DType, Int32Type>) {
+    uint32_t u;
+    std::memcpy(&u, &src, sizeof(u));
+    u = ::arrow::bit_util::ToLittleEndian(u);
+    dst->assign(reinterpret_cast<const char*>(&u), sizeof(u));
+    return;
+  } else if constexpr (std::is_same_v<DType, Int64Type>) {
+    uint64_t u;
+    std::memcpy(&u, &src, sizeof(u));
+    u = ::arrow::bit_util::ToLittleEndian(u);
+    dst->assign(reinterpret_cast<const char*>(&u), sizeof(u));
+    return;
+  } else if constexpr (std::is_same_v<DType, FloatType>) {
+    uint32_t u;
+    static_assert(sizeof(u) == sizeof(float), "size");
+    std::memcpy(&u, &src, sizeof(u));
+    u = ::arrow::bit_util::ToLittleEndian(u);
+    dst->assign(reinterpret_cast<const char*>(&u), sizeof(u));
+    return;
+  } else if constexpr (std::is_same_v<DType, DoubleType>) {
+    uint64_t u;
+    static_assert(sizeof(u) == sizeof(double), "size");
+    std::memcpy(&u, &src, sizeof(u));
+    u = ::arrow::bit_util::ToLittleEndian(u);
+    dst->assign(reinterpret_cast<const char*>(&u), sizeof(u));
+    return;
+  }
+#endif
+
+  // Fallback: use encoder for other types
   auto encoder = MakeTypedEncoder<DType>(Encoding::PLAIN, false, descr_, pool_);
   encoder->Put(&src, 1);
   auto buffer = encoder->FlushValues();
@@ -934,6 +967,35 @@ void TypedStatisticsImpl<DType>::PlainEncode(const T& src, std::string* dst) con
 
 template <typename DType>
 void TypedStatisticsImpl<DType>::PlainDecode(const std::string& src, T* dst) const {
+#if !ARROW_LITTLE_ENDIAN
+  if constexpr (std::is_same_v<DType, Int32Type>) {
+    uint32_t u = 0;
+    std::memcpy(&u, src.data(), std::min(src.size(), sizeof(u)));
+    u = ::arrow::bit_util::FromLittleEndian(u);
+    std::memcpy(dst, &u, sizeof(u));
+    return;
+  } else if constexpr (std::is_same_v<DType, Int64Type>) {
+    uint64_t u = 0;
+    std::memcpy(&u, src.data(), std::min(src.size(), sizeof(u)));
+    u = ::arrow::bit_util::FromLittleEndian(u);
+    std::memcpy(dst, &u, sizeof(u));
+    return;
+  } else if constexpr (std::is_same_v<DType, FloatType>) {
+    uint32_t u = 0;
+    std::memcpy(&u, src.data(), std::min(src.size(), sizeof(u)));
+    u = ::arrow::bit_util::FromLittleEndian(u);
+    std::memcpy(dst, &u, sizeof(u));
+    return;
+  } else if constexpr (std::is_same_v<DType, DoubleType>) {
+    uint64_t u = 0;
+    std::memcpy(&u, src.data(), std::min(src.size(), sizeof(u)));
+    u = ::arrow::bit_util::FromLittleEndian(u);
+    std::memcpy(dst, &u, sizeof(u));
+    return;
+  }
+#endif
+
+  // Fallback: use decoder for other types
   auto decoder = MakeTypedDecoder<DType>(Encoding::PLAIN, descr_);
   decoder->SetData(1, reinterpret_cast<const uint8_t*>(src.c_str()),
                    static_cast<int>(src.size()));