cpp<int C, int S, int I, int L, int LL>DescriptionThis policy is used to promote safe types in arithmetic expressions
according to the rules in the C++ standard. But rather than using the
native C++ standard types supported by the compiler, it uses types whose
length in number of bits is specified by the template parameters.This policy is useful for running test programs which use C++
portable integer types but which are destined to run on an architecture
which is different than the one on which the test program is being built
and run. This can happen when developing code for embedded systems.
Algorithms developed or borrowed from one architecture but destined for
another can be tested on the desktop.Note that this policy is only applicable to safe types whose base
type is a type fulfilling the type requirements of Integer.Template ParametersParameterTypeDescriptionCintNumber of bits in a charSintNumber of bits in a shortIintNumber of bits in an integerLintNumber of bits in a longLLintNumber of bits in a long longModel ofPromotionPolicyExample of UseConsider the following problem. One is developing software which
uses a very small microprocessor and a very limited C compiler. The chip
is so small, you can't print anything from the code, log, debug or
anything else. One debugs this code by using the "burn" and "crash" method
- you burn the chip (download the code), run the code, observe the
results, make changes and try again. This is a crude method which is
usually the one used. But it can be quite time consuming.Consider an alternative. Build and compile your code in testable
modules. For each module write a test which exercises all the code and
makes it work. Finally download your code into the chip and - voilĂ -
working product. This sounds great, but there's one problem. Our target
processor - in this case a PIC162550 from Microchip Technology is only an
8 bit CPU. The compiler we use defines INT as 8 bits. This (and a few
other problems), make our algorithm testing environment differ from our
target environment. We can address this by defining INT as a safe integer
with a range of 8 bits. By using a custom promotion policy, we can force
the evaluation of C++ expressions in the test environment to be the same
as that in the target environment. Also in our target environment, we can
trap any overflows or other errors. So we can write and test our code on
our desktop system and download the code to the target knowing that it
just has to work. This is a huge time saver and confidence builder. For an
extended example on how this is done, look at Safety
Critical Embedded Controller .Header#include
<boost/numeric/safe_numerics/cpp.hpp>