Big endian fix, thanks to @hyperair for hints and initial implementation.

xs/src/admesh/stl.h

@@ -26,11 +26,6 @@
 #include <stdio.h>
 #include <stdint.h>
 #include <stddef.h>
-#include <boost/detail/endian.hpp>
-
-#ifndef BOOST_LITTLE_ENDIAN
-#error "admesh works correctly on little endian machines only!"
-#endif
 
 #define STL_MAX(A,B) ((A)>(B)? (A):(B))
 #define STL_MIN(A,B) ((A)<(B)? (A):(B))
@@ -112,7 +107,7 @@ typedef struct {
 typedef struct {
   char          header[81];
   stl_type      type;
-  int           number_of_facets;
+  uint32_t      number_of_facets;
   stl_vertex    max;
   stl_vertex    min;
   stl_vertex    size;

xs/src/admesh/stl_io.cpp

@@ -23,9 +23,9 @@
 #include <stdlib.h>
 #include <string.h>
 #include "stl.h"
-//#include "config.h"
 
 #include <boost/nowide/cstdio.hpp>
+#include <boost/detail/endian.hpp>
 
 #if !defined(SEEK_SET)
 #define SEEK_SET 0
@@ -204,6 +204,17 @@ stl_print_neighbors(stl_file *stl, char *file) {
   fclose(fp);
 }
 
+#ifndef BOOST_LITTLE_ENDIAN
+// Swap a buffer of 32bit data from little endian to big endian and vice versa.
+void stl_internal_reverse_quads(char *buf, size_t cnt)
+{
+  for (size_t i = 0; i < cnt; i += 4) {
+    std::swap(buf[i], buf[i+3]);
+    std::swap(buf[i+1], buf[i+2]);
+  }
+}
+#endif
+
 void
 stl_write_binary(stl_file *stl, const char *file, const char *label) {
   FILE      *fp;
@@ -229,9 +240,23 @@ stl_write_binary(stl_file *stl, const char *file, const char *label) {
   for(i = strlen(label); i < LABEL_SIZE; i++) putc(0, fp);
 
   fseek(fp, LABEL_SIZE, SEEK_SET);
+#ifdef BOOST_LITTLE_ENDIAN
   fwrite(&stl->stats.number_of_facets, 4, 1, fp);
-  for(i = 0; i < stl->stats.number_of_facets; i++)
+  for (i = 0; i < stl->stats.number_of_facets; ++ i)
     fwrite(stl->facet_start + i, SIZEOF_STL_FACET, 1, fp);
+#else /* BOOST_LITTLE_ENDIAN */
+  char buffer[50];
+  // Convert the number of facets to little endian.
+  memcpy(buffer, &stl->stats.number_of_facets, 4);
+  stl_internal_reverse_quads(buffer, 4);
+  fwrite(buffer, 4, 1, fp);
+  for (i = 0; i < stl->stats.number_of_facets; ++ i) {
+    memcpy(buffer, stl->facet_start + i, 50);
+    // Convert to little endian.
+    stl_internal_reverse_quads(buffer, 48);
+    fwrite(buffer, SIZEOF_STL_FACET, 1, fp);
+  }
+#endif /* BOOST_LITTLE_ENDIAN */
   fclose(fp);
 }
 

xs/src/admesh/stlinit.cpp

@@ -27,6 +27,7 @@
 #include <assert.h>
 
 #include <boost/nowide/cstdio.hpp>
+#include <boost/detail/endian.hpp>
 
 #include "stl.h"
 
@@ -50,11 +51,15 @@ stl_initialize(stl_file *stl) {
   stl->stats.volume = -1.0;
 }
 
+#ifndef BOOST_LITTLE_ENDIAN
+extern void stl_internal_reverse_quads(char *buf, size_t cnt);
+#endif /* BOOST_LITTLE_ENDIAN */
+
 void
 stl_count_facets(stl_file *stl, const char *file) {
   long           file_size;
   int            header_num_facets;
-  int            num_facets;
+  uint32_t       num_facets;
   int            i;
   size_t         s;
   unsigned char  chtest[128];
@@ -113,7 +118,12 @@ stl_count_facets(stl_file *stl, const char *file) {
     }
 
     /* Read the int following the header.  This should contain # of facets */
-    if((!fread(&header_num_facets, sizeof(int), 1, stl->fp)) || (num_facets != header_num_facets)) {
+    bool header_num_faces_read = fread(&header_num_facets, sizeof(uint32_t), 1, stl->fp);
+#ifndef BOOST_LITTLE_ENDIAN
+    // Convert from little endian to big endian.
+    stl_internal_reverse_quads((char*)&header_num_facets, 4);
+#endif /* BOOST_LITTLE_ENDIAN */
+    if (! header_num_faces_read || num_facets != header_num_facets) {
       fprintf(stderr,
               "Warning: File size doesn't match number of facets in the header\n");
     }
@@ -268,6 +278,10 @@ stl_read(stl_file *stl, int first_facet, int first) {
         stl->error = 1;
         return;
       }
+#ifndef BOOST_LITTLE_ENDIAN
+      // Convert the loaded little endian data to big endian.
+      stl_internal_reverse_quads((char*)&facet, 48);
+#endif /* BOOST_LITTLE_ENDIAN */
     } else
       /* Read a single facet from an ASCII .STL file */
     {