Add code to perform overflow-checking additions and multiplication

Most processors have carry flags which they set on addition overflow, so
it's a good idea to access them whenever possible. Most of them also
have widening multiply instructions that can be used to detect overflow
of the non-widening version.

Tested to compile on:
 Architecture     Compiler
  x86             GCC 4.9, GCC 5*, Clang 3.6*, ICC 16 beta
  x86-64          GCC 4.9, GCC 5*, Clang 3.6*, ICC 16 beta
  x86-64 ILP32    GCC 4.9, GCC 5*, Clang 3.6*
  IA-64 LP64      GCC 4.8
  ARMv7-A         GCC 4.9, Clang 3.6*
  AArch64         Clang 3.6*
  MIPS            GCC 4.9, Clang 3.6*
  MIPS64          GCC 4.9, Clang 3.6*
  PowerPC         GCC 4.9, Clang 3.6*
  PowerPC 64      GCC 4.9, Clang 3.6*
  SPARC           Clang 3.6*
  SPARCv9         Clang 3.6*

[*] supports the intrinsics

If the compiler does not offer a way to detect an overflow, we do it by
hand. For unsigned additions, that's easy, since the C++ language
specifies the behavior of the overflow. That's also the reason why this
code is implemented only for unsigned integers.

For the multiplication, if the compiler does not support widening
multiplications, we do it with a division instead. This is necessary for
GCC < 4.5 and compilers not compatible with GCC or MSVC.

Change-Id: I049a653beeb5454c9539ffff13e637de0f1338c1
Reviewed-by: Ulf Hermann <ulf.hermann@theqtcompany.com>
Reviewed-by: Alex Trotsenko <alex1973tr@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/corelib/global/qglobal.h b/src/corelib/global/qglobal.h
index f8f306f614..6ee3e37ce6 100644
--- a/src/corelib/global/qglobal.h
+++ b/src/corelib/global/qglobal.h
@@ -448,6 +448,9 @@ template <>    struct QIntegerForSize<1> { typedef quint8  Unsigned; typedef qin
 template <>    struct QIntegerForSize<2> { typedef quint16 Unsigned; typedef qint16 Signed; };
 template <>    struct QIntegerForSize<4> { typedef quint32 Unsigned; typedef qint32 Signed; };
 template <>    struct QIntegerForSize<8> { typedef quint64 Unsigned; typedef qint64 Signed; };
+#if defined(Q_CC_GNU) && defined(__SIZEOF_INT128__)
+template <>    struct QIntegerForSize<16> { __extension__ typedef unsigned __int128 Unsigned; __extension__ typedef __int128 Signed; };
+#endif
 template <class T> struct QIntegerForSizeof: QIntegerForSize<sizeof(T)> { };
 typedef QIntegerForSize<Q_PROCESSOR_WORDSIZE>::Signed qregisterint;
 typedef QIntegerForSize<Q_PROCESSOR_WORDSIZE>::Unsigned qregisteruint;