[boost] Re: datetime and long long

From: Markus Schöpflin (markus.schoepflin_at_[hidden])
Date: 2003-02-19 04:44:34

David Abrahams wrote:

> "Jeff Garland" <jeff_at_[hidden]> writes:
> 
> 
>>> Many of the regression tests for the date time library are
>>> failing currently because the library relies on std::abs<long
>>> long> being available. AKAIK, the C++ standard doesn't require
>>> this so the library shouldn't make use of it.
>>> 
>>> Maybe datetime should specify it's own version of abs like
>>> this:
>>> 
>>> #include <cstdlib>
>>> #include <stdlib.h>
 >>>
>>> template <typename T> T abs(T i) { return std::abs(i); } 
>>> template <> long long abs(long long i) {return ::llabs(i); }
>> 
>> Take a look at bosot/date_time/compiler_config.hpp which does
>> something similar.  All we need to do to fix these regressions is
>> add the compiler to the list of those that don't have std::abs at
>> line 34.  Turns out that some compilers that support long long do
>> define a version of abs for long long.  (I'm sure you also know
>> that some compilers don't call it the type long long either which
>> is why we have boost::int64_t).
>> 
>> Just as an aside, at some point this logic should likely move out
>> of date_time and into the general config somewhere so that others
>> can access std::abs on these types if they need.
> 
> AFAICT the logic is backwards:  you should assume there's no
> std::abs which works on long long and use your own function by
> default, only using std::abs if the compiler is *known* to support
> that extension... if it's even worth the trouble (it'll be less
> code to just do the whole thing yourself).

Looks like there a two cases which would need two macros.

- BOOST_NO_STD_ABS identifies that no std::abs is available.

- BOOST_HAS_STD_ABS_LONG_LONG identifies that the compiler provides a 
long long overload for std::abs.

Those macro names follow the general macro naming convention, I think.

The easiest thing would probably be to just say

namespace whatever { inline template <class T> T abs(T) { ... } }

and use this, as Dave suggested.

Markus