Re: [boost] Promote Traits -- Review of Generic Image Library (GIL)

From: David Greene (greened_at_[hidden])
Date: 2006-10-17 16:51:21

Ullrich Koethe wrote:

>> For example, VIGRA's promotion traits choose double as the promotion for
>> int when dealing with floating point operations. Why not float? On many
>> architectures float is faster, and precision may not be an issue in the
>> context in which you use it.

>> Why should int always be the result type of adding two ints? 
> 
> Because that's what the C++ standard says (AFAIR).

But the standard isn't always the best answer for all promotion
situations.  For example, some years back I wrote some expression
template code for simulation purposes.  I wanted a simple user
interface so I promoted int / int to double to avoid loss of
precision.

Stuffed away in some cobweb-infested dusty disk sector I have a
library that implements promotion "strategies" using a table-driven
configuration of (operator/operand type -> promotion type) rules.
I'll see if I can dig it out and post it as a starting point.  I'm
not sure if it's what we want as a Boost library but it might be a
start for discussion.

                    -Dave