From 8a0eee50e37de52c7b8ae4d68088e213190a45b2 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Sat, 7 Mar 2015 03:20:07 +1100
Subject: [PATCH] point: add from function

---
 point.cpp | 17 +++++++++++++++--
 point.hpp |  1 +
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/point.cpp b/point.cpp
index 104e55fc..56c56e8f 100644
--- a/point.cpp
+++ b/point.cpp
@@ -28,10 +28,11 @@
 using namespace std;
 
 
-//-----------------------------------------------------------------------------
+///////////////////////////////////////////////////////////////////////////////
 template <size_t S, typename T>
 util::vector<S,T>
-util::point<S,T>::to (const point<S,T> &rhs) const {
+util::point<S,T>::to (const point<S,T> &rhs) const
+{
     util::vector<S,T> out;
 
     for (size_t i = 0; i < S; ++i)
@@ -42,6 +43,18 @@ util::point<S,T>::to (const point<S,T> &rhs) const {
 
 //-----------------------------------------------------------------------------
 template <size_t S, typename T>
+util::vector<S,T>
+util::point<S,T>::from (const point<S,T> &rhs) const
+{
+    util::vector<S,T> out;
+    for (size_t i = 0; i < S; ++i)
+        out.data[i] = this->data[i] - rhs.data[i];
+    return out;
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+template <size_t S, typename T>
 void
 util::point<S,T>::sanity (void) const {
     CHECK (std::all_of (begin (this->data),
diff --git a/point.hpp b/point.hpp
index 7c3b68b1..87ab14e2 100644
--- a/point.hpp
+++ b/point.hpp
@@ -42,6 +42,7 @@ namespace util {
         template <typename U> typename std::common_type<T,U>::type manhattan (const point<S,U> &) const;
 
         vector<S,T> to (const point&) const;
+        vector<S,T> from (const point&) const;
 
         template <size_t D> point<D,T> redim (void) const;
         template <size_t D> point<D,T> redim (const util::point<D,T> &fill) const;