From 25933a55455b2a0927769b29d06e3b2779e3efb6 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 16 Dec 2015 18:18:22 +0200
Subject: Bugfix: accuracy loss in ODB mapping for butl:timestamp

---
 brep/package | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/brep/package b/brep/package
index 056e2a8..8a9dcb2 100644
--- a/brep/package
+++ b/brep/package
@@ -6,8 +6,10 @@
 #define BREP_PACKAGE
 
 #include <map>
+#include <ratio>
 #include <chrono>
-#include <iosfwd>  // ostream
+#include <iosfwd>      // ostream
+#include <type_traits> // static_assert
 
 #include <odb/core.hxx>
 #include <odb/forward.hxx>  // database
@@ -90,9 +92,23 @@ namespace brep
   #pragma db map type(dir_path) as(string)     \
     to((?).string ()) from(brep::dir_path (?))
 
-  #pragma db map type(timestamp) as(uint64_t)        \
-    to(std::chrono::system_clock::to_time_t (?))     \
-    from(std::chrono::system_clock::from_time_t (?))
+  // Ensure that timestamp can be represented in nonoseconds without loss of
+  // accuracy, so the following ODB mapping is adequate.
+  //
+  static_assert(
+    std::ratio_greater_equal<timestamp::period,
+                             std::chrono::nanoseconds::period>::value,
+    "The following timestamp ODB mapping is invalid");
+
+  // As it pointed out in butl/timestamp we will overflow in year 2262 but
+  // by that time some larger basic type will be available for mapping.
+  //
+  #pragma db map type(timestamp) as(uint64_t)                 \
+    to(std::chrono::duration_cast<std::chrono::nanoseconds> ( \
+         (?).time_since_epoch ()).count ())                   \
+    from(brep::timestamp (                                    \
+      std::chrono::duration_cast<brep::timestamp::duration> ( \
+        std::chrono::nanoseconds (?))))
 
   // version
   //
-- 
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