[Flang] Shift the data from lower to higher order bits in the big endian environment (llvm#73670)

Shift the data from lower to higher order bits when memcpy the value in
the namelist in the big endian environment

---------

Co-authored-by: Mark Danial <mark.danial@ibm.com>
Co-authored-by: Kelvin Li <kli@ca.ibm.com>

Author: madanial0

flang/include/flang/Common/uint128.h

@@ -33,15 +33,18 @@ template <bool IS_SIGNED = false> class Int128 {
   constexpr Int128(unsigned n) : low_{n} {}
   constexpr Int128(unsigned long n) : low_{n} {}
   constexpr Int128(unsigned long long n) : low_{n} {}
-  constexpr Int128(int n)
-      : low_{static_cast<std::uint64_t>(n)}, high_{-static_cast<std::uint64_t>(
-                                                 n < 0)} {}
-  constexpr Int128(long n)
-      : low_{static_cast<std::uint64_t>(n)}, high_{-static_cast<std::uint64_t>(
-                                                 n < 0)} {}
-  constexpr Int128(long long n)
-      : low_{static_cast<std::uint64_t>(n)}, high_{-static_cast<std::uint64_t>(
-                                                 n < 0)} {}
+  constexpr Int128(int n) {
+    low_ = static_cast<std::uint64_t>(n);
+    high_ = -static_cast<std::uint64_t>(n < 0);
+  }
+  constexpr Int128(long n) {
+    low_ = static_cast<std::uint64_t>(n);
+    high_ = -static_cast<std::uint64_t>(n < 0);
+  }
+  constexpr Int128(long long n) {
+    low_ = static_cast<std::uint64_t>(n);
+    high_ = -static_cast<std::uint64_t>(n < 0);
+  }
   constexpr Int128(const Int128 &) = default;
   constexpr Int128(Int128 &&) = default;
   constexpr Int128 &operator=(const Int128 &) = default;
@@ -246,7 +249,10 @@ template <bool IS_SIGNED = false> class Int128 {
   }
 
 private:
-  constexpr Int128(std::uint64_t hi, std::uint64_t lo) : low_{lo}, high_{hi} {}
+  constexpr Int128(std::uint64_t hi, std::uint64_t lo) {
+    low_ = lo;
+    high_ = hi;
+  }
   constexpr int LeadingZeroes() const {
     if (high_ == 0) {
       return 64 + LeadingZeroBitCount(low_);
@@ -255,7 +261,13 @@ template <bool IS_SIGNED = false> class Int128 {
     }
   }
   static constexpr std::uint64_t topBit{std::uint64_t{1} << 63};
+#if FLANG_LITTLE_ENDIAN
   std::uint64_t low_{0}, high_{0};
+#elif FLANG_BIG_ENDIAN
+  std::uint64_t high_{0}, low_{0};
+#else
+#error host endianness is not known
+#endif
 };
 
 using UnsignedInt128 = Int128<false>;

flang/runtime/edit-input.cpp

@@ -244,7 +244,16 @@ bool EditIntegerInput(
     value = -value;
   }
   if (any || !io.GetConnectionState().IsAtEOF()) {
-    std::memcpy(n, &value, kind); // a blank field means zero
+    // The value is stored in the lower order bits on big endian platform.
+    // When memcpy, shift the value to the higher order bit.
+    auto shft{static_cast<int>(sizeof(value.low())) - kind};
+    // For kind==8 (i.e. shft==0), the value is stored in low_ in big endian.
+    if (!isHostLittleEndian && shft >= 0) {
+      auto l{value.low() << (8 * shft)};
+      std::memcpy(n, &l, kind);
+    } else {
+      std::memcpy(n, &value, kind); // a blank field means zero
+    }
   }
   return any;
 }