Fix BinaryReader on BE (#17893)

Fix BinaryReader on BE

The ints passed into the int array ctor needed to be endian swapped.
Interestingly, the BinaryWriter implementation currently being used
(not refsrc AFAIK) does this on write just fine.

Fixes ReadDecimal test on AIX, and adds another test to ensure that
Write(decimal) can be read back by ReadDecimal in case.

1 files changed, 7 insertions, 0 deletions

diff --git a/mcs/class/referencesource/mscorlib/system/io/binaryreader.cs b/mcs/class/referencesource/mscorlib/system/io/binaryreader.cs
index e4e1ecfe376..9f1b89de5d5 100644
--- a/mcs/class/referencesource/mscorlib/system/io/binaryreader.cs
+++ b/mcs/class/referencesource/mscorlib/system/io/binaryreader.cs
@@ -23,6 +23,7 @@ namespace System.IO {
     using System.Globalization;
     using System.Diagnostics.Contracts;
     using System.Security;
+    using System.Buffers.Binary;
 
 [System.Runtime.InteropServices.ComVisible(true)]
     public class BinaryReader : IDisposable
@@ -243,6 +244,12 @@ namespace System.IO {
             try {
                 int[] ints = new int[4];
                 Buffer.BlockCopy(m_buffer, 0, ints, 0, 16);
+                if (!BitConverter.IsLittleEndian) {
+                    // We need to reverse the ints on BE
+                    for (int i = 0; i < 4; i++) {
+                         ints[i] = BinaryPrimitives.ReverseEndianness(ints[i]);
+                    }
+                }
                 return new decimal(ints);
             }
             catch (ArgumentException e) {