Add safe_cast (RIPD-1702):

This change ensures that no overflow can occur when casting
between enums and integral types.

src/ripple/basics/impl/Sustain.cpp

@@ -17,6 +17,7 @@
 */
 //==============================================================================
 
+#include <ripple/basics/safe_cast.h>
 #include <ripple/basics/Sustain.h>
 #include <ripple/beast/core/CurrentThreadName.h>
 #include <boost/format.hpp>
@@ -41,8 +42,8 @@ namespace ripple {
 static auto const sleepBeforeWaiting = 10;
 static auto const sleepBetweenWaits = 1;
 
-static pid_t pManager = static_cast<pid_t> (0);
-static pid_t pChild = static_cast<pid_t> (0);
+static pid_t pManager = safe_cast<pid_t> (0);
+static pid_t pChild = safe_cast<pid_t> (0);
 
 static void pass_signal (int a)
 {

src/ripple/basics/safe_cast.h

@@ -0,0 +1,78 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of rippled: https://github.com/ripple/rippled
+    Copyright (c) 2018 Ripple Labs Inc.
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#ifndef RIPPLE_BASICS_SAFE_CAST_H_INCLUDED
+#define RIPPLE_BASICS_SAFE_CAST_H_INCLUDED
+
+#include <type_traits>
+
+namespace ripple {
+
+// safe_cast adds compile-time checks to a static_cast to ensure that
+// the destination can hold all values of the source.  This is particularly
+// handy when the source or destination is an enumeration type.
+
+template <class Dest, class Src>
+inline
+constexpr
+std::enable_if_t
+<
+    std::is_integral<Dest>::value && std::is_integral<Src>::value,
+    Dest
+>
+safe_cast(Src s) noexcept
+{
+    static_assert(std::is_signed<Dest>::value || std::is_unsigned<Src>::value,
+        "Cannot cast signed to unsigned");
+    constexpr unsigned not_same = std::is_signed<Dest>::value !=
+                                  std::is_signed<Src>::value;
+    static_assert(sizeof(Dest) >= sizeof(Src) + not_same,
+        "Destination is too small to hold all values of source");
+    return static_cast<Dest>(s);
+}
+
+template <class Dest, class Src>
+inline
+constexpr
+std::enable_if_t
+<
+    std::is_enum<Dest>::value && std::is_integral<Src>::value,
+    Dest
+>
+safe_cast(Src s) noexcept
+{
+    return static_cast<Dest>(safe_cast<std::underlying_type_t<Dest>>(s));
+}
+
+template <class Dest, class Src>
+inline
+constexpr
+std::enable_if_t
+<
+    std::is_integral<Dest>::value && std::is_enum<Src>::value,
+    Dest
+>
+safe_cast(Src s) noexcept
+{
+    return safe_cast<Dest>(static_cast<std::underlying_type_t<Src>>(s));
+}
+
+} // ripple
+
+#endif