From 2fabfad4438d346cf6b77f25a05b71a5326a577a Mon Sep 17 00:00:00 2001
From: Gawain Bolton <45885849+gawain-bolton@users.noreply.github.com>
Date: Thu, 10 Oct 2019 22:07:48 +0200
Subject: [PATCH] Improve performance of adding and subtracting time durations
 from a ptime. (#99)

Modifying ptime objects by adding and subtracting time durations was
inefficient because it extracted the date and time of day and then
re-constructed a ptime using the date and modified time of day.

This can be avoided by using the existing time_system utilities which
perform the operation by adjusting the number of ticks.

Performance is improved by a factor of 48 on my system.
---
 include/boost/date_time/time.hpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/boost/date_time/time.hpp b/include/boost/date_time/time.hpp
index 632f10d7f..1eafe8810 100644
--- a/include/boost/date_time/time.hpp
+++ b/include/boost/date_time/time.hpp
@@ -164,7 +164,7 @@ namespace date_time {
     }
     time_type operator+=(const time_duration_type& td)
     {
-      time_ = (time_system::get_time_rep(date(), time_of_day() + td));
+      time_ = time_system::add_time_duration(time_,td);
       return time_type(time_);
     }
     //! subtract time durations
@@ -174,7 +174,7 @@ namespace date_time {
     }
     time_type operator-=(const time_duration_type& td) 
     {
-      time_ = (time_system::get_time_rep(date(), time_of_day() - td));
+      time_ = time_system::subtract_time_duration(time_, td);
       return time_type(time_);
     }