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On 08/13/11 09:52 PM, Dmitry A. Kazakov wrote: > On Sat, 13 Aug 2011 21:29:05 +1200, Ian Collins wrote: > >> It's pretty rare for the application domain to be concerned about >> the semantics of an integer beyond those specified by the language. > > If buffer overflows and code quality is not a concern, then yes. Most variables have limited scope and a well defined range. So if I use an int in a for loop over a small set of data, I'm not writing poor quality code. >>>>> In each such case I will have to use a type different from the machine >>>>> type. This is just another argument why types need to be precisely >>>>> specified. I addressed this issue above. >>>> >>>> But they are precisely specified on any given platform. >>> >>> 1. They are not. In order to see the specification of int, you have to read >>> the compiler documentation. My point was that the program code does not >>> specify the properties of int. The answer that it is defined somewhere >>> somehow is not an argument at all, anything works in this or that way. >> >> If you want to get the best performance out of a given platform (which >> many C and C++ programs do), you have to program to the characteristics >> of the platform. > > First of all, performance is not a functional requirement. It very often is the first one for most of the embedded systems I write! > If functional > requirements are not met, non-functional ones are irrelevant. The functional requirements are irrelevant if they can not be met in the required time. > Thus the > question stands: what does int implement? Where in the program code is any > specification of the *functional* requirements which the implementation > chosen to be int is supposed to fulfill [in the best etc possible way, > which in its turn requires validation]? How do I know if int is OK, not > unsigned, not long, not short and so on? In general, you can't. Where it matters, you have to measure. > Secondly, how do you know that int gives you the best performance across > all possible implementations fulfilling the functional requirements? By > choosing int you prohibit the compiler to select any other machine type, > which also does the things you want. The point is, specify what you want > and let the compiler to implement it in a best possible way. Choosing an > implementation is an optimization issue, you can aim at memory use, at > time, at best lock-free sharing and so on. Fixing a machine type makes your > program potentially less efficient. More precisely you specify the > semantics of required type, more knowledge the compiler has to generate > efficient code. I do see your point and for C or C++ the best we can do knowing a variable is signed or unsigned of a given range is to use one of the C fast_xx types. Far from ideal I know. Yes I agree being able to specify a type without reference to an underlying fundamental type is a powerful feature C and C++ lack. -- Ian Collins
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