[Issue 12169] sum(int[]) should return a int

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=12169


timon.gehr at gmx.ch changed:

           What    |Removed                     |Added
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                 CC|                            |timon.gehr at gmx.ch


--- Comment #5 from timon.gehr at gmx.ch 2014-02-16 07:00:53 PST ---
(In reply to comment #1)
> This is by design in the code, presumably to avoid overflow (which you are
> usually so concerned about, what changed?)
> 
> I actually agree with you though. I'd expect sum!(int[]) to return int. In
> general, I'd expect sum!(T[]) to return typeof(T.init + T.init), and respect
> the language integral promotions.
> ...

+1.

(In reply to comment #2)
> If sum returned int for ranges of int, it would be 100% identical to
> std.algorithm.reduce.

Not yet, there are more special cases. (but a more general divide and conquer
reduction algorithm might be an useful addition.)

BTW: D semantics do not seem to support Kahan summation. (Walter has expressed
in the past that any operation might arbitrarily be performed at higher
precision.)

> It's worth returning a 64-bit quantity because
> (a) 64-bit summing is about as fast as 32-bit summing,
> (b) the result can be cast to int if needed.
> 

IMO it's not worth the special casing. (Another thing I find questionable:
extending range capabilities can reduce precision.) Allowing specification of
the summation type is enough.

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