If tmp2 and final files are in same filesystem, rename() not copy() (#…

…314)

* If the tmp2 and final files are in the same filesystem, rename() instead of
copy() into place.

* Final file doesn't exist yet, need to stat the parent directory

* gcc is able to convert that value for stat(2), but Windows needs a
reinterpret_cast.  Add that.

Co-authored-by: Chris Ross <cross+chia@distal.com>

src/plotter_disk.hpp

@@ -23,6 +23,7 @@
 
 #include <math.h>
 #include <stdio.h>
+#include <sys/stat.h>
 
 #include <algorithm>
 #include <fstream>
@@ -370,7 +371,13 @@ class DiskPlotter {
         Timer copy;
         do {
             std::error_code ec;
-            if (tmp_2_filename.parent_path() == final_filename.parent_path()) {
+            struct stat tmp2_stat, final_stat;
+            int rc;
+            rc = ::stat(reinterpret_cast<const char *>(tmp_2_filename.c_str()), &tmp2_stat);
+            if (rc == 0)
+                rc = ::stat(reinterpret_cast<const char *>(final_filename.parent_path().c_str()), &final_stat);
+            if ((rc == 0 && tmp2_stat.st_dev == final_stat.st_dev) ||
+                tmp_2_filename.parent_path() == final_filename.parent_path()) {
                 fs::rename(tmp_2_filename, final_filename, ec);
                 if (ec.value() != 0) {
                     std::cout << "Could not rename " << tmp_2_filename << " to " << final_filename