From 25696b7fb338f87045154a27e223f896c67c53a4 Mon Sep 17 00:00:00 2001
From: Howard Hinnant <howard.hinnant@gmail.com>
Date: Tue, 24 Oct 2017 15:44:41 -0400
Subject: [PATCH] Optimize to_stream for zoned_time

* Decrease the number of lookups in the database from 2 to 1.
---
 include/date/tz.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/date/tz.h b/include/date/tz.h
index 1387bf1b..6d6a2c2f 100644
--- a/include/date/tz.h
+++ b/include/date/tz.h
@@ -1774,8 +1774,13 @@ std::basic_ostream<CharT, Traits>&
 to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
           const zoned_time<Duration, TimeZonePtr>& tp)
 {
-    auto const info = tp.get_info();
-    return to_stream(os, fmt, tp.get_local_time(), &info.abbrev, &info.offset);
+    using duration = typename zoned_time<Duration, TimeZonePtr>::duration;
+    using LT = local_time<duration>;
+    auto const tz = tp.get_time_zone();
+    auto const st = tp.get_sys_time();
+    auto const info = tz->get_info(st);
+    return to_stream(os, fmt, LT{(st+info.offset).time_since_epoch()},
+                     &info.abbrev, &info.offset);
 }
 
 template <class CharT, class Traits, class Duration, class TimeZonePtr>