From 70906ad75321cf313dbb37e14ab7cf7cddd4c6b7 Mon Sep 17 00:00:00 2001
From: Jose Luis Blanco-Claraco <jlblanco@ual.es>
Date: Thu, 31 Aug 2017 14:35:10 +0200
Subject: [PATCH] import bit_cast<>

---
 libs/base/include/mrpt/utils/bit_cast.h | 79 +++++++++++++++++++++++++
 packaging/debian/copyright              |  5 ++
 2 files changed, 84 insertions(+)
 create mode 100644 libs/base/include/mrpt/utils/bit_cast.h

diff --git a/libs/base/include/mrpt/utils/bit_cast.h b/libs/base/include/mrpt/utils/bit_cast.h
new file mode 100644
index 0000000000..0c41305c04
--- /dev/null
+++ b/libs/base/include/mrpt/utils/bit_cast.h
@@ -0,0 +1,79 @@
+/* +------------------------------------------------------------------------+
+   |                     Mobile Robot Programming Toolkit (MRPT)            |
+   |                          http://www.mrpt.org/                          |
+   |                                                                        |
+   | Copyright (c) 2005-2017, Individual contributors, see AUTHORS file     |
+   | See: http://www.mrpt.org/Authors - All rights reserved.                |
+   | Released under BSD License. See details in http://www.mrpt.org/License |
+   +------------------------------------------------------------------------+ */
+
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+#ifndef BASE_BIT_CAST_H_
+#define BASE_BIT_CAST_H_
+#include <string.h>
+#include <type_traits>
+#include "base/compiler_specific.h"
+#include "base/template_util.h"
+#include "build/build_config.h"
+// bit_cast<Dest,Source> is a template function that implements the equivalent
+// of "*reinterpret_cast<Dest*>(&source)".  We need this in very low-level
+// functions like the protobuf library and fast math support.
+//
+//   float f = 3.14159265358979;
+//   int i = bit_cast<int32_t>(f);
+//   // i = 0x40490fdb
+//
+// The classical address-casting method is:
+//
+//   // WRONG
+//   float f = 3.14159265358979;            // WRONG
+//   int i = * reinterpret_cast<int*>(&f);  // WRONG
+//
+// The address-casting method actually produces undefined behavior according to
+// the ISO C++98 specification, section 3.10 ("basic.lval"), paragraph 15.
+// (This did not substantially change in C++11.)  Roughly, this section says: if
+// an object in memory has one type, and a program accesses it with a different
+// type, then the result is undefined behavior for most values of "different
+// type".
+//
+// This is true for any cast syntax, either *(int*)&f or
+// *reinterpret_cast<int*>(&f).  And it is particularly true for conversions
+// between integral lvalues and floating-point lvalues.
+//
+// The purpose of this paragraph is to allow optimizing compilers to assume that
+// expressions with different types refer to different memory.  Compilers are
+// known to take advantage of this.  So a non-conforming program quietly
+// produces wildly incorrect output.
+//
+// The problem is not the use of reinterpret_cast.  The problem is type punning:
+// holding an object in memory of one type and reading its bits back using a
+// different type.
+//
+// The C++ standard is more subtle and complex than this, but that is the basic
+// idea.
+//
+// Anyways ...
+//
+// bit_cast<> calls memcpy() which is blessed by the standard, especially by the
+// example in section 3.9 .  Also, of course, bit_cast<> wraps up the nasty
+// logic in one place.
+//
+// Fortunately memcpy() is very fast.  In optimized mode, compilers replace
+// calls to memcpy() with inline object code when the size argument is a
+// compile-time constant.  On a 32-bit system, memcpy(d,s,4) compiles to one
+// load and one store, and memcpy(d,s,8) compiles to two loads and two stores.
+template <class Dest, class Source>
+inline Dest bit_cast(const Source& source) {
+  static_assert(sizeof(Dest) == sizeof(Source),
+                "bit_cast requires source and destination to be the same size");
+  static_assert(base::is_trivially_copyable<Dest>::value,
+                "bit_cast requires the destination type to be copyable");
+  static_assert(base::is_trivially_copyable<Source>::value,
+                "bit_cast requires the source type to be copyable");
+  Dest dest;
+  memcpy(&dest, &source, sizeof(dest));
+  return dest;
+}
+#endif  // BASE_BIT_CAST_H_
\ No newline at end of file
diff --git a/packaging/debian/copyright b/packaging/debian/copyright
index c4642d2bd3..47204f5ccd 100644
--- a/packaging/debian/copyright
+++ b/packaging/debian/copyright
@@ -756,3 +756,8 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  * rplidar: Low-cost LiDAR driver
  Copyright (c) 2014 - 2016 Shanghai Slamtec Co., Ltd.
   2-clause BSD License
+
+ * libs/base/include/mrpt/utils/bit_cast.h
+  Copyright 2016 The Chromium Authors. All rights reserved.
+  Use of this source code is governed by a BSD-style license that can be
+  found in the LICENSE file.