From 4891c6af0e964bdbaf549bc2c7bd038ccee1bb73 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Wed, 15 Jun 2011 22:38:58 +1000
Subject: [PATCH] Add sign_cast functions

These safely cast between signed and unsigned numeric quantities,
aborting if the result cannot be safely converted (as opposed to size
expanding or throwing).
---
 types.hpp | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/types.hpp b/types.hpp
index f101a529..afee0e5a 100644
--- a/types.hpp
+++ b/types.hpp
@@ -3,6 +3,7 @@
 
 #include <cstdint>
 #include <string>
+#include <limits>
 
 template <int BITS>
 struct bits_type;
@@ -53,4 +54,43 @@ template <typename T>
 std::string type_to_string (void);
 
 
+template <typename T>
+struct sign_types;
+
+
+template <> struct sign_types <signed int> {
+    typedef   signed int with_sign;
+    typedef unsigned int without_sign;
+};
+
+
+template <> struct sign_types <unsigned int> {
+    typedef   signed int with_sign;
+    typedef unsigned int without_sign;
+};
+
+
+/// Safely cast a numeric type to its signed comparison, aborting if the
+/// result is not representable.
+template <typename T>
+typename sign_types<T>::with_sign
+sign_cast (const typename sign_types<T>::without_sign v)
+{
+    check_hard (v <= std::numeric_limits<typename sign_types<T>::without_sign>::max () >> 1);
+    return static_cast <typename sign_types<T>::with_sign> (v);
+}
+
+
+/// Safely cast a numeric type to its unsigned comparison, aborting if the
+/// result is not representable.
+template <typename T>
+typename sign_types<T>::without_sign
+sign_cast (const typename sign_types<T>::with_sign v)
+{
+    check_hard (v >= 0);
+    return static_cast <typename sign_types<T>::without_sign> (v);
+}
+
+
+
 #endif // __TYPES_HPP