1 files changed, 43 insertions, 1 deletions
diff --git a/butl/filesystem.cxx b/butl/filesystem.cxx
index 230bc8e..7c8893e 100644
--- a/butl/filesystem.cxx
+++ b/butl/filesystem.cxx
@@ -4,7 +4,7 @@
 
 #include <butl/filesystem>
 
-#include <unistd.h>    // rmdir(), unlink()
+#include <unistd.h>    // stat, rmdir(), unlink()
 #include <sys/types.h> // stat
 #include <sys/stat.h>  // stat, lstat(), S_IS*, mkdir()
 
@@ -14,6 +14,48 @@ using namespace std;
 
 namespace butl
 {
+  // Figuring out whether we have the nanoseconds in some form.
+  //
+  template <typename S>
+  constexpr auto nsec (const S* s) -> decltype(s->st_mtim.tv_nsec)
+  {
+    return s->st_mtim.tv_nsec; // POSIX (GNU/Linux, Solaris).
+  }
+
+  template <typename S>
+  constexpr auto nsec (const S* s) -> decltype(s->st_mtimespec.tv_nsec)
+  {
+    return s->st_mtimespec.tv_nsec; // MacOS X.
+  }
+
+  template <typename S>
+  constexpr auto nsec (const S* s) -> decltype(s->st_mtime_n)
+  {
+    return s->st_mtime_n; // AIX 5.2 and later.
+  }
+
+  template <typename S>
+  constexpr int nsec (...) {return 0;}
+
+  timestamp
+  file_mtime (const path& p)
+  {
+    struct stat s;
+    if (::lstat (p.string ().c_str (), &s) != 0)
+    {
+      if (errno == ENOENT || errno == ENOTDIR)
+        return timestamp_nonexistent;
+      else
+        throw system_error (errno, system_category ());
+    }
+
+    return S_ISREG (s.st_mode)
+      ? system_clock::from_time_t (s.st_mtime) +
+      chrono::duration_cast<duration> (
+        chrono::nanoseconds (nsec<struct stat> (&s)))
+      : timestamp_nonexistent;
+  }
+
   bool
   dir_exists (const path& p)
   {