From 8ca5d1f676d9632ae286b43d9b0c5d45592ff385 Mon Sep 17 00:00:00 2001
From: Bradley Lowekamp <blowekamp@mail.nih.gov>
Date: Wed, 19 Apr 2023 14:23:23 -0400
Subject: [PATCH] BUG: MRC write full machine stamp

The MRC2014 specification updated/clarifed the spec that the first two
bytes should contain the specified value to determine endian. This
appears to be enforced with Python mrcfile. This patch enables
compatibility.
---
 Modules/IO/MRC/include/itkMRCHeaderObject.h | 4 ++--
 Modules/IO/MRC/src/itkMRCImageIO.cxx        | 2 ++
 Modules/IO/MRC/test/itkMRCImageIOTest2.cxx  | 3 +++
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/Modules/IO/MRC/include/itkMRCHeaderObject.h b/Modules/IO/MRC/include/itkMRCHeaderObject.h
index 6b95976ce7d..23cd3357486 100644
--- a/Modules/IO/MRC/include/itkMRCHeaderObject.h
+++ b/Modules/IO/MRC/include/itkMRCHeaderObject.h
@@ -164,8 +164,8 @@ class ITKIOMRC_EXPORT MRCHeaderObject : public LightObject
     float zorg;
 
     char cmap[4];  /**< Contains "MAP "  */
-    char stamp[4]; /**< First byte has 17 for big- or 68 for
-                     little-endian  */
+    char stamp[4]; /**< First two bytes have 17 and 17 for big-endian or
+                        68 and 68 for little-endian */
     float rms;
 
     // ALL HEADERS:
diff --git a/Modules/IO/MRC/src/itkMRCImageIO.cxx b/Modules/IO/MRC/src/itkMRCImageIO.cxx
index f866f37e9e5..5293963d67a 100644
--- a/Modules/IO/MRC/src/itkMRCImageIO.cxx
+++ b/Modules/IO/MRC/src/itkMRCImageIO.cxx
@@ -358,10 +358,12 @@ MRCImageIO::UpdateHeaderFromImageIO()
   if (ByteSwapper<void *>::SystemIsBigEndian())
   {
     header.stamp[0] = 17;
+    header.stamp[1] = 17;
   }
   else
   {
     header.stamp[0] = 68;
+    header.stamp[1] = 68;
   }
 
   header.alpha = 90;
diff --git a/Modules/IO/MRC/test/itkMRCImageIOTest2.cxx b/Modules/IO/MRC/test/itkMRCImageIOTest2.cxx
index 2a16dbee158..444d8c4f546 100644
--- a/Modules/IO/MRC/test/itkMRCImageIOTest2.cxx
+++ b/Modules/IO/MRC/test/itkMRCImageIOTest2.cxx
@@ -24,6 +24,9 @@
 #include "itkMetaDataObject.h"
 #include "itkTestingHashImageFilter.h"
 
+
+static_assert(sizeof(itk::MRCHeaderObject::Header) == 1024, " Ill defined MRC Header struct");
+
 namespace
 {