From 5cc317cdab432d670c823f3399ef0efed9c38867 Mon Sep 17 00:00:00 2001
From: Christian Henning <chhenning@gmail.com>
Date: Sat, 6 Nov 2010 18:17:10 +0000
Subject: [PATCH] Introducing base_channel_type metafunction which helps to
 avoid useless casting between integral data types. For older compilers it
 also reduces warnings about those castings operations.

[SVN r66416]
---
 include/boost/gil/channel.hpp           | 27 +++++++++++++++++++++++++
 include/boost/gil/channel_algorithm.hpp |  6 +++---
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/include/boost/gil/channel.hpp b/include/boost/gil/channel.hpp
index 823691b35..d8cf78c79 100644
--- a/include/boost/gil/channel.hpp
+++ b/include/boost/gil/channel.hpp
@@ -27,6 +27,7 @@
 #include <limits>
 #include <cassert>
 #include <boost/cstdint.hpp>
+#include <boost/type_traits/remove_cv.hpp>
 #include "gil_config.hpp"
 #include "utilities.hpp"
 
@@ -669,4 +670,30 @@ struct is_integral<gil::scoped_channel_value<BaseChannelValue,MinVal,MaxVal> > :
 
 }
 
+// \brief Determines the fundamental type which may be used, e.g., to cast from larger to smaller channel types.
+namespace boost { namespace gil {
+template <typename T>
+struct base_channel_type_impl { typedef T type; };
+
+template <int N>
+struct base_channel_type_impl<packed_channel_value<N> >
+{ typedef typename packed_channel_value<N>::integer_t type; };
+
+template <typename B, int F, int N, bool M>
+struct base_channel_type_impl<packed_channel_reference<B, F, N, M> >
+{ typedef typename packed_channel_reference<B,F,N,M>::integer_t type; };
+
+template <typename B, int N, bool M>
+struct base_channel_type_impl<packed_dynamic_channel_reference<B, N, M> >
+{ typedef typename packed_dynamic_channel_reference<B,N,M>::integer_t type; };
+
+template <typename ChannelValue, typename MinV, typename MaxV>
+struct base_channel_type_impl<scoped_channel_value<ChannelValue, MinV, MaxV> >
+{ typedef ChannelValue type; };
+
+template <typename T>
+struct base_channel_type : base_channel_type_impl<typename remove_cv<T>::type > {};
+
+} } //namespace boost::gil
+
 #endif
diff --git a/include/boost/gil/channel_algorithm.hpp b/include/boost/gil/channel_algorithm.hpp
index 1361219a3..8d39fafdf 100644
--- a/include/boost/gil/channel_algorithm.hpp
+++ b/include/boost/gil/channel_algorithm.hpp
@@ -226,8 +226,8 @@ struct channel_converter_unsigned_integral_impl<SrcChannelV,DstChannelV,SrcLessT
 template <typename SrcChannelV, typename DstChannelV> 
 struct channel_converter_unsigned_integral_nondivisible<SrcChannelV,DstChannelV,true,false> {
     DstChannelV operator()(SrcChannelV src) const {
-        typedef typename detail::min_fast_uint<unsigned_integral_num_bits<SrcChannelV>::value+unsigned_integral_num_bits<DstChannelV>::value>::type integer_t;
-        return DstChannelV(integer_t(src * unsigned_integral_max_value<DstChannelV>::value) / unsigned_integral_max_value<SrcChannelV>::value);
+        typedef typename base_channel_type<DstChannelV>::type dest_t;
+        return DstChannelV(static_cast<dest_t>( src * unsigned_integral_max_value<DstChannelV>::value) / unsigned_integral_max_value<SrcChannelV>::value);
     }
 };
 
@@ -410,7 +410,7 @@ assert(mul == 64);    // 64 = 128 * 128 / 255
 template <typename ChannelValue>
 struct channel_multiplier_unsigned : public std::binary_function<ChannelValue,ChannelValue,ChannelValue> {
     ChannelValue operator()(ChannelValue a, ChannelValue b) const {
-        return ChannelValue(a / double(channel_traits<ChannelValue>::max_value()) * b);
+        return ChannelValue(static_cast<typename base_channel_type<ChannelValue>::type>(a / double(channel_traits<ChannelValue>::max_value()) * b));
     }
 };