Don Clugston wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
>> Don Clugston wrote:
>>> Andrei Alexandrescu (See Website For Email) wrote:
>>>> A while ago, C++ did the mistake of defining std::numeric_limits<T>::min() with a different semantics for floating-point types than for integral types. That hurt generic numeric code a lot.
>>>>
>>>> D has taken over the same mistake: T.min means the smallest value of the type, except for floating-point types, where it means the smallest positive value.
>>>>
>>>> The right way is to have T.min always return the minimum value (duh) and define a separate property T.min_positive.
>>>>
>>>> The question is, would a lot of code be hurt by such a change?
>>>>
>>>>
>>>> Andrei
>>>
>>> It probably wouldn't break a huge amount of D code, but I don't think there would be many cases where T.min for a floating point type would be useful. More significant is the problems involved in converting from C or Fortran code to D.
>>
>> I'm not even discussing the utility of min_positive. All I'm saying is that if you say "min", you should return "min", particularly when others do exactly that.
>>
>>> On a more profound level...
>>> I'm not aware of many cases where it's possible to treat integer and floating-points generically. People often try, but usually the code is incorrect for the floating point types, since the semantics are completely different. (For example, I don't know why x++ is legal for floating point types; I think it's just a newbie trap; you have no guarantee that x++ is different to x).
>>>
>>> What type of generic numeric code did you have in mind? What are the benefits which would come by such a change?
>>
>> Trivially simple: the min and max functions. For min, the code picks the type with the smallest .min. For max, the code picks the type with the largest .max.
> 
> Obviously, but are there many other functions like that? Also, you really should treat floating point as a special case, anyway, because of the possibility of a NaN.

There was another example (computing the minimum of a nonempty collection). But to me the issue is a tad different: (1) the name is clearly misused; (2) it's easy to fix; (3) not fixing it sends the wrong message ("we carried over whatever was in C++ on numerics"). D takes pride in taking care of minutiae. It's odd to have the smorgasbord of floating-point operators that D has (how often did _you_ use !<>=?) yet at the same time say, "oh, min? that's not really min. I was kidding."

> I'd be surprised if the total benefit amounted to more than a few dozen lines of library code.
> 
> There's also the issue of complex types. Currently, this passes:
> 
> static assert(creal.max == real.max+1i*real.max);

Ouch.


Andrei

Andrei Alexandrescu (See Website For Email) wrote:
> Don Clugston wrote:
>> Andrei Alexandrescu (See Website For Email) wrote:
>>> Don Clugston wrote:
>>>> Andrei Alexandrescu (See Website For Email) wrote:
>>>>> A while ago, C++ did the mistake of defining std::numeric_limits<T>::min() with a different semantics for floating-point types than for integral types. That hurt generic numeric code a lot.
>>>>>
>>>>> D has taken over the same mistake: T.min means the smallest value of the type, except for floating-point types, where it means the smallest positive value.
>>>>>
>>>>> The right way is to have T.min always return the minimum value (duh) and define a separate property T.min_positive.
>>>>>
>>>>> The question is, would a lot of code be hurt by such a change?
>>>>>
>>>>>
>>>>> Andrei
>>>>
>>>> It probably wouldn't break a huge amount of D code, but I don't think there would be many cases where T.min for a floating point type would be useful. More significant is the problems involved in converting from C or Fortran code to D.
>>>
>>> I'm not even discussing the utility of min_positive. All I'm saying is that if you say "min", you should return "min", particularly when others do exactly that.
>>>
>>>> On a more profound level...
>>>> I'm not aware of many cases where it's possible to treat integer and floating-points generically. People often try, but usually the code is incorrect for the floating point types, since the semantics are completely different. (For example, I don't know why x++ is legal for floating point types; I think it's just a newbie trap; you have no guarantee that x++ is different to x).
>>>>
>>>> What type of generic numeric code did you have in mind? What are the benefits which would come by such a change?
>>>
>>> Trivially simple: the min and max functions. For min, the code picks the type with the smallest .min. For max, the code picks the type with the largest .max.
>>
>> Obviously, but are there many other functions like that? Also, you really should treat floating point as a special case, anyway, because of the possibility of a NaN.
> 
> There was another example (computing the minimum of a nonempty collection). But to me the issue is a tad different: (1) the name is clearly misused; (2) it's easy to fix; (3) not fixing it sends the wrong message ("we carried over whatever was in C++ on numerics"). D takes
> pride in taking care of minutiae. It's odd to have the smorgasbord of floating-point operators that D has (how often did _you_ use !<>=?) yet at the same time say, "oh, min? that's not really min. I was kidding.

Point taken. I'd support this if at the same time, the bizarre out-by-1 error in min_exp and max_exp was fixed. My code contains quite a few instances of (real.min_exp/2) because I actually wanted the genuine minimum exponent.
Then we could say that all normalised numbers x satisfy
pow(2, real.min_exp) <= x < pow(2, real.max_exp+1).

Possibly even rename the current real.min to be real.min_normal, since it isn't even the smallest representable value > 0.

Andrei Alexandrescu (See Website For Email) wrote:

> Don Clugston wrote:
>> Andrei Alexandrescu (See Website For Email) wrote:
>>> Don Clugston wrote:
>>>> Andrei Alexandrescu (See Website For Email) wrote:
>>>>> A while ago, C++ did the mistake of defining std::numeric_limits<T>::min() with a different semantics for floating-point types than for integral types. That hurt generic numeric code a lot.
>>>>>
>>>>> D has taken over the same mistake: T.min means the smallest value of the type, except for floating-point types, where it means the smallest positive value.
>>>>>
>>>>> The right way is to have T.min always return the minimum value (duh) and define a separate property T.min_positive.
>>>>>
>>>>> The question is, would a lot of code be hurt by such a change?
>>>>>
>>>>>
>>>>> Andrei
>>>>
>>>> It probably wouldn't break a huge amount of D code, but I don't think there would be many cases where T.min for a floating point type would be useful. More significant is the problems involved in converting from C or Fortran code to D.
>>>
>>> I'm not even discussing the utility of min_positive. All I'm saying is that if you say "min", you should return "min", particularly when others do exactly that.
>>>
>>>> On a more profound level...
>>>> I'm not aware of many cases where it's possible to treat integer and
>>>> floating-points generically. People often try, but usually the code
>>>> is incorrect for the floating point types, since the semantics are
>>>> completely different. (For example, I don't know why x++ is legal for
>>>> floating point types; I think it's just a newbie trap; you have no
>>>> guarantee that x++ is different to x).
>>>>
>>>> What type of generic numeric code did you have in mind? What are the benefits which would come by such a change?
>>>
>>> Trivially simple: the min and max functions. For min, the code picks the type with the smallest .min. For max, the code picks the type with the largest .max.
>> 
>> Obviously, but are there many other functions like that? Also, you really should treat floating point as a special case, anyway, because of the possibility of a NaN.
> 
> There was another example (computing the minimum of a nonempty
> collection). But to me the issue is a tad different: (1) the name is
> clearly misused; (2) it's easy to fix; (3) not fixing it sends the wrong
> message ("we carried over whatever was in C++ on numerics").

And what about carrying over that const mess from C++? If const as a keyword is to stay - just let it mean constant - nothing else.

> D takes
> pride in taking care of minutiae. It's odd to have the smorgasbord of
> floating-point operators that D has (how often did _you_ use !<>=?) yet
> at the same time say, "oh, min? that's not really min. I was kidding."

!<>= is in use in Tango as it seems to what is actually happening when looking for NaN :)

-- 
Lars Ivar Igesund
blog at http://larsivi.net
DSource, #d.tango & #D: larsivi
Dancing the Tango

Andrei Alexandrescu (See Website For Email) wrote:
> It's odd to have the smorgasbord of floating-point operators that D has (how often did _you_ use !<>=?) yet 
Since you ask...
With a quick grep through 2 directories I found three uses, with <>= being used 12 times.
But I'm not normal. <g>.

Don Clugston wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
>> It's odd to have the smorgasbord of floating-point operators that D has (how often did _you_ use !<>=?) yet 
> Since you ask...
> With a quick grep through 2 directories I found three uses, with <>= being used 12 times.
> But I'm not normal. <g>.

Ok, now search for !>=. :o)

Andrei

Don Clugston wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
>> It's odd to have the smorgasbord of floating-point operators that D has (how often did _you_ use !<>=?) yet 
> Since you ask...
> With a quick grep through 2 directories I found three uses, with <>= being used 12 times.
> But I'm not normal. <g>.

That's why your opinion on fp issues carries a lot of weight here - you're a professional numerics programmer, and those are unusual.

Don Clugston wrote:
> 0ffh wrote:
>> [...]
>> Of course if you have a *very* big number, that might mean it's the same.... sometimes I do faster typing than thinking... :)
> Exactly -- that's the trap.

Faster typing than thinking? Sure! :-))))

(Sorry, couldn't resist!)

Greetz, Frank