Re: Fastest minimum-width integer types and limits macros

[Gunther Nikl <gnikl at users dot sourceforge dot net>]

Ian Lance Taylor wrote:
> Gunther Nikl <gnikl@users.sourceforge.net> writes:
> 
>> Here is an example for int_fast8_t:
>>
>>   typedef signed char int_fast8_t;
>>   #define INT_FAST8_MIN INT8_MIN
>>   #define INT_FAST8_MAX INT8_MAX
>>
>> Now if int_fast8_t uses "int" as underlying type like this:
>>
>>   typedef int int_fast8_t;
>>
>> which value is its MIN/MAX macros supposed to have? Is it
>> allowed to use the same "char" limits as above or do I need
>> to use
>>
>>   #define INT_FAST8_MIN INT32_MIN
>>   #define INT_FAST8_MAX INT32_MAX
>>
>> in that case?
>>
>> So this is not about user code but an implementation question.
> 
> The value of INT_FAST8_MIN is implementation defined, so you can choose
> whatever value you like (as long as it is <= -128).  That said, the
> standard seems to suggest that the value should correspond to the value
> of the underlying type.  That is, if int_fast8_t is defined as int, then
> the value of INT_FAST8_MIN should be INT_MIN.  That at least makes
> INT_FAST8_MIN useful, as otherwise it would always simply have the
> value -128.

Thanks for the information about the standard. FWIW, I assumed that if
a fast 8bit type was requested than its only about a 8bit value range
and thus the 8bit limits are sufficient.

Regards,
Gunthr Nikl