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>
29bc68cf16